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Sample records for calcite seed crystals

  1. Crystal lattice tilting in prismatic calcite.

    PubMed

    Olson, Ian C; Metzler, Rebecca A; Tamura, Nobumichi; Kunz, Martin; Killian, Christopher E; Gilbert, Pupa U P A

    2013-08-01

    We analyzed the calcitic prismatic layers in Atrina rigida (Ar), Haliotis iris (Hi), Haliotis laevigata (HL), Haliotis rufescens (Hrf), Mytilus californianus (Mc), Pinctada fucata (Pf), Pinctada margaritifera (Pm) shells, and the aragonitic prismatic layer in the Nautilus pompilius (Np) shell. Dramatic structural differences were observed across species, with 100-μm wide single-crystalline prisms in Hi, HL and Hrf, 1-μm wide needle-shaped calcite prisms in Mc, 1-μm wide spherulitic aragonite prisms in Np, 20-μm wide single-crystalline calcite prisms in Ar, and 20-μm wide polycrystalline calcite prisms in Pf and Pm. The calcite prisms in Pf and Pm are subdivided into sub-prismatic domains of orientations, and within each of these domains the calcite crystal lattice tilts gradually over long distances, on the order of 100 μm, with an angle spread of crystal orientation of 10-20°. Furthermore, prisms in Pf and Pm are harder than in any other calcite prisms analyzed, their nanoparticles are smaller, and the angle spread is strongly correlated with hardness in all shells that form calcitic prismatic layers. One can hypothesize a causal relationship of these correlated parameters: greater angle spread may confer greater hardness and resistance to wear, thus providing Pf and Pm with a structural advantage in their environment. This is the first structure-property relationship thus far hypothesized in mollusk shell prisms.

  2. Visualization of acoustic cavitation effects on suspended calcite crystals.

    PubMed

    Wagterveld, R M; Boels, L; Mayer, M J; Witkamp, G J

    2011-01-01

    The acoustic cavitation (42,080 Hz, 7.1 W cm(-2) or 17 W) effects on suspended calcite crystals, sized between 5 and 50 μm, have been visualized for the first time using high speed photography. High speed recordings with a duration of 1 s containing up to 300,000 frames per second, revealed the effect of cluster and streamer cavitation on several calcite crystals. Cavitation clusters, evolved from cavitation inception and collapse, caused attrition, disruption of aggregates and deagglomeration, whereas streamer cavitation was observed to cause deagglomeration only. Cavitation on the surface gave the crystals momentum. However, it is shown that breakage of accelerated crystals by interparticle collisions is unrealistic because of their small sizes and low velocities. Crystals that were accelerated by bubble expansion, subsequently experienced a deceleration much stronger than expected from drag forces, upon bubble collapse. Experiments with pre-dried crystals seemed to support the current theory on bubble nucleation through the presence of pre-existing gas pockets. However, experiments with fully wetted crystals also showed the nucleation of bubbles on the crystal surface. Although microjet impingement on the crystal surface could not be directly visualized with high speed photography, scanning electron microscopy (SEM) analysis of irradiated calcite seeds showed deep circular indentations. It was suggested that these indentations might be caused by shockwave induced jet impingement. Furthermore, the appearance of voluminous fragments with large planes of fracture indicated that acoustic cavitation can also cause the breakage of single crystal structures.

  3. Interactions of salicylic acid derivatives with calcite crystals.

    PubMed

    Ukrainczyk, Marko; Gredičak, Matija; Jerić, Ivanka; Kralj, Damir

    2012-01-01

    Investigation of basic interactions between the active pharmaceutical compounds and calcium carbonates is of great importance because of the possibility to use the carbonates as a mineral carrier in drug delivery systems. In this study the mode and extent of interactions of salicylic acid and its amino acid derivates, chosen as pharmaceutically relevant model compounds, with calcite crystals are described. Therefore, the crystal growth kinetics of well defined rhombohedral calcite seed crystals in the systems containing salicylic acid (SA), 5-amino salicylic acid (5-ASA), N-salicyloil-l-aspartic acid (N-Sal-Asp) or N-salicyloil-l-glutamic acid (N-Sal-Glu), were investigated. The precipitation systems were of relatively low initial supersaturation and of apparently neutral pH. The data on the crystal growth rate reductions in the presence of the applied salicylate molecules were analyzed by means of Cabrera & Vermileya's, and Kubota & Mullin's models of interactions of the dissolved additives and crystal surfaces. The crystal growth kinetic experiments were additionally supported with the appropriate electrokinetic, spectroscopic and adsorption measurements. The Langmuir adsorption constants were determined and they were found to be in a good correlation with values obtained from crystal growth kinetic analyses. The results indicated that salicylate molecules preferentially adsorb along the steps on the growing calcite surfaces. The values of average spacing between the adjacent salicylate adsorption active sites and the average distance between the neighboring adsorbed salicylate molecules were also estimated.

  4. Crystal growth of calcite from calcium bicarbonate solutions at constant PCO2 and 25°C: a test of a calcite dissolution model

    USGS Publications Warehouse

    Reddy, Michael M.; Plummer, L. Neil; Busenberg, E.

    1981-01-01

    A highly reproducible seeded growth technique was used to study calcite crystallization from calcium bicarbonate solutions at 25°C and fixed carbon dioxide partial pressures between 0.03 and 0.3 atm. The results are not consistent with empirical crystallization models that have successfully described calcite growth at low PCO2 (< 10−3 atm). Good agreement was found between observed crystallization rates and those calculated from the calcite dissolution rate law and mechanism proposed by Plummer et al. (1978).

  5. Calcite crystal growth rate inhibition by polycarboxylic acids

    USGS Publications Warehouse

    Reddy, M.M.; Hoch, A.R.

    2001-01-01

    Calcite crystal growth rates measured in the presence of several polycarboxyclic acids show that tetrahydrofurantetracarboxylic acid (THFTCA) and cyclopentanetetracarboxylic acid (CPTCA) are effective growth rate inhibitors at low solution concentrations (0.01 to 1 mg/L). In contrast, linear polycarbocylic acids (citric acid and tricarballylic acid) had no inhibiting effect on calcite growth rates at concentrations up to 10 mg/L. Calcite crystal growth rate inhibition by cyclic polycarboxyclic acids appears to involve blockage of crystal growth sites on the mineral surface by several carboxylate groups. Growth morphology varied for growth in the absence and in the presence of both THFTCA and CPTCA. More effective growth rate reduction by CPTCA relative to THFTCA suggests that inhibitor carboxylate stereochemical orientation controls calcite surface interaction with carboxylate inhibitors. ?? 20O1 Academic Press.

  6. Crystallization on prestructured seeds.

    PubMed

    Jungblut, Swetlana; Dellago, Christoph

    2013-01-01

    The crystallization transition of an undercooled monodisperse Lennard-Jones fluid in the presence of small prestructured seeds is studied with transition path sampling combined with molecular dynamics simulations. Compared to the homogeneous crystallization, clusters of a few particles arranged into a face- and body-centered cubic structure enhance the crystallization, while icosahedrally ordered seeds do not change the reaction rate. We identify two distinct nucleation regimes-close to the seed and in the bulk. Crystallites form close to the face- and body-centered structures and tend to stay away from the icosahedrally ordered seeds.

  7. Crystal growth of aragonite and calcite in presence of citric acid, DTPA, EDTA and pyromellitic acid.

    PubMed

    Westin, K-J; Rasmuson, A C

    2005-02-15

    The influence of four calcium complexing substances, i.e., citric acid (CIT), diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA) and pyromellitic acid (PMA), on the crystal growth rate of the calcium carbonate polymorphs aragonite and calcite has been studied. Using a seeded constant supersaturation method supersaturation was maintained at 4 by keeping a constant pH of 8.5 through addition of sodium carbonate and calcium chloride solutions. The unique composition of each solution was calculated using chemical speciation. The growth rate was interpreted in terms of an overall growth rate. For both calcite and aragonite, the crystal growth rate is significantly reduced in the presence of the calcium complexing substances. The growth retarding effect depends on both the concentration and the polymorph. The relative crystal growth rate was correlated to the total complexing agent concentration using a Langmuir adsorption approach. Aragonite appeared fully covered for lower total concentrations than calcite. Furthermore, CIT very efficiently blocked aragonite growth contrary to what was observed for calcite. This is thought to be related to certain distinct features of the dominant aragonite crystal faces compared to the dominant calcite faces.

  8. On the origin of fiber calcite crystals in moonmilk deposits.

    PubMed

    Cañaveras, Juan Carlos; Cuezva, Soledad; Sanchez-Moral, Sergio; Lario, Javier; Laiz, Leonila; Gonzalez, Juan Miguel; Saiz-Jimenez, Cesareo

    2006-01-01

    In this study, we show that moonmilk subaerial speleothems in Altamira Cave (Spain) consist of a network of fiber calcite crystals and active microbial structures. In Altamira moonmilks, the study of the typology and distribution of fiber crystals, extracellular polymeric substances, and microorganisms allowed us to define the initial stages of fiber crystal formation in recent samples as well as the variations in the microstructural arrangement in more evolved stages. Thus, we have been able to show the existence of a relationship among the different types of fiber crystals and their origins. This allowed us to outline a model that illustrates the different stages of formation of the moonmilk, developed on different substrata, concluding that microbes influence physicochemical precipitation, resulting in a variety of fiber crystal morphologies and sizes.

  9. The effect of sulfated polysaccharides on the crystallization of calcite superstructures

    NASA Astrophysics Data System (ADS)

    Fried, Ruth; Mastai, Yitzhak

    2012-01-01

    Calcite with unique morphology and uniform size has been successfully synthesized in the presence of classes of polysaccharides based on carrageenans. In the crystallization of calcite, the choice of different carrageenans, (iota, lambda and kappa), as additives concedes systematic study of the influence of different chemical structures and particularly molecular charge on the formation of CaCO 3 crystals. The uniform calcite superstructures are formed by assemblies and aggregation of calcite crystals. The mechanism for the formation of calcite superstructures was studied by a variety of techniques, SEM, TEM, XRD, time-resolved conductivity and light scattering measurements, focusing on the early stages of crystals' nucleation and aggregation.

  10. Functionalizing single crystals: incorporation of nanoparticles inside gel-grown calcite crystals.

    PubMed

    Liu, Yujing; Yuan, Wentao; Shi, Ye; Chen, Xiaoqiang; Wang, Yong; Chen, Hongzheng; Li, Hanying

    2014-04-14

    Synthetic single crystals are usually homogeneous solids. Biogenic single crystals, however, can incorporate biomacromolecules and become inhomogeneous solids so that their properties are also extrinsically regulated by the incorporated materials. The discrepancy between the properties of synthetic and biogenic single crystals leads to the idea to modify the internal structure of synthetic crystals to achieve nonintrinsic properties by incorporation of foreign material. Intrinsically colorless and diamagnetic calcite single crystals are turned into colored and paramagnetic solids, through incorporation of Au and Fe3O4 nanoparticles without significantly disrupting the crystalline lattice of calcite. The crystals incorporate the nanoparticles and gel fibers when grown in agarose gel media containing the nanoparticles, whereas the solution-grown crystals do not. As such, our work extends the long-history gel method for crystallization into a platform to functionalize single-crystalline materials.

  11. Crystallographic orientation inhomogeneity and crystal splitting in biogenic calcite

    PubMed Central

    Checa, Antonio G.; Bonarski, Jan T.; Willinger, Marc G.; Faryna, Marek; Berent, Katarzyna; Kania, Bogusz; González-Segura, Alicia; Pina, Carlos M.; Pospiech, Jan; Morawiec, Adam

    2013-01-01

    The calcitic prismatic units forming the outer shell of the bivalve Pinctada margaritifera have been analysed using scanning electron microscopy–electron back-scatter diffraction, transmission electron microscopy and atomic force microscopy. In the initial stages of growth, the individual prismatic units are single crystals. Their crystalline orientation is not consistent but rather changes gradually during growth. The gradients in crystallographic orientation occur mainly in a direction parallel to the long axis of the prism, i.e. perpendicular to the shell surface and do not show preferential tilting along any of the calcite lattice axes. At a certain growth stage, gradients begin to spread and diverge, implying that the prismatic units split into several crystalline domains. In this way, a branched crystal, in which the ends of the branches are independent crystalline domains, is formed. At the nanometre scale, the material is composed of slightly misoriented domains, which are separated by planes approximately perpendicular to the c-axis. Orientational gradients and splitting processes are described in biocrystals for the first time and are undoubtedly related to the high content of intracrystalline organic molecules, although the way in which these act to induce the observed crystalline patterns is a matter of future research. PMID:23804442

  12. Magnesium-Calcite Crystal Formation Mediated by the Thermophilic Bacterium Geobacillus thermoglucosidasius Requires Calcium and Endospores.

    PubMed

    Murai, Rie; Yoshida, Naoto

    2016-11-01

    Fresh Geobacillus thermoglucosidasius cells grown on soybean-casein digest nutrient agar were inoculated as a parent colony 1 cm in diameter on the surface of an agar gel containing acetate and calcium ions (calcite-promoting hydrogel) and incubated at 60 °C for 4 days, after which magnesium-calcite single crystals of 50-130 µm in size formed within the parent colony. Addition of EDTA, polyacrylic acid or N,N-dicyclohexylcarbodiimide to the calcite-forming hydrogel inhibited the parent colony from forming magnesium-calcite crystals. Inoculation of G. thermoglucosidasius on calcite-forming hydrogel containing 5 µM cadmium and 20 µM zinc resulted in a decrease in the sporulation rate from 55 to 7-8 %. Magnesium-calcite synthesis decreased relative to the sporulation rate. G. thermoglucosidasius exhibited higher adsorption/absorbance of calcium than other Geobacillus sp. that do not mediate calcite formation and higher levels of magnesium accumulation. Calcium ions contained in the calcite-promoting hydrogel and magnesium ions concentrated in G. thermoglucosidasius cells serve as the elements for magnesium-calcite synthesis. The observed decreases in sporulation rate and magnesium-calcite formation support the hypothesis that endospores act as nuclei for the synthesis of magnesium-calcite single crystals.

  13. Struvite and calcite crystallization induced by cellular membranes of Myxococcus xanthus

    NASA Astrophysics Data System (ADS)

    González-Muñoz, Ma Teresa; Omar, Nabil Ben; Martínez-Cañamero, Magdalena; Rodríguez-Gallego, Manuel; Galindo, Alberto López; Arias, JoséMa

    1996-06-01

    In this work we have proved that struvite and calcite crystals can be obtained in the presence of the cellular membrane fraction of Myxococcus xanthus, when appropriate supersaturated solutions are used. Probably, the negative charged points of the external side of the cellular structures could reduce the metastability field of struvite and calcite, acting as heterogeneous nuclei of crystallization.

  14. Crystal-protein interactions studied by overgrowth of calcite on biogenic skeletal elements

    NASA Astrophysics Data System (ADS)

    Aizenberg, J.; Albeck, S.; Weiner, S.; Addadi, L.

    1994-09-01

    A key parameter in the biological control of crystal formation is the interaction of a group of acidic macromolecules with the mineral phase. Here we study protein-calcite interactions using epitaxial overgrowth of synthetic calcite crystals under conditions in which local release of occluded macromolecules from the biogenic substrate occurs. The macromolecules subsequently interact with the newly formed overgrown crystals, resulting in modified calcite morphology. This novel method provides a means of mapping crystal-protein interactions under conditions that minimally affect the conformational states of the acidic macromolecules. We show that proteins released from calcitic sponge spicules and mollusc prisms specifically interact with {001} and {01 l} faces of calcite, whereas proteins released from echinoderm skeletal elements only interact with {01 l} faces. The extent to which the overgrown crystals are affected by the proteins varies even in the same organism and within the same element, depending on the site and crystallographic orientation of the skeletal elements.

  15. Evaluation of strengthening mechanisms in calcite single crystals from mollusk shells.

    PubMed

    Kunitake, Miki E; Mangano, Lauren M; Peloquin, John M; Baker, Shefford P; Estroff, Lara A

    2013-02-01

    Biogenic single-crystal calcite is often reported to be harder and tougher than geologic calcite in the form of Iceland spar. However, the mechanistic origins of the superior mechanical properties of the biogenic materials are still debated. We investigate the hardness and modulus of biogenic calcite from the prismatic layer of the mollusk Atrina rigida compared with a pure geologic calcite, Iceland spar. On the {001} face, biogenic calcite is found to be 50-70% harder than geologic calcite. This range is due to the fact that changes in azimuthal angle of the indenter tip lead to a hardness variation of ∼20% in A. rigida but only ∼7% in Iceland spar. The higher hardness and increased anisotropy of biogenic calcite could be accounted for by hardening mechanisms based on hindered dislocation motion rather than crack deflection.

  16. An assessment of calcite crystal growth mechanisms based on crystal size distributions

    USGS Publications Warehouse

    Kile, D.E.; Eberl, D.D.; Hoch, A.R.; Reddy, M.M.

    2000-01-01

    Calcite crystal growth experiments were undertaken to test a recently proposed model that relates crystal growth mechanisms to the shapes of crystal size distributions (CSDs). According to this approach, CSDs for minerals have three basic shapes: (1) asymptotic, which is related to a crystal growth mechanism having constant-rate nucleation accompanied by surface-controlled growth; (2) lognormal, which results from decaying-rate nucleation accompanied by surface-controlled growth; and (3) a theoretical, universal, steady-state curve attributed to Ostwald ripening. In addition, there is a fourth crystal growth mechanism that does not have a specific CSD shape, but which preserves the relative shapes of previously formed CSDs. This mechanism is attributed to supply-controlled growth. All three shapes were produced experimentally in the calcite growth experiments by modifying nucleation conditions and solution concentrations. The asymptotic CSD formed when additional reactants were added stepwise to the surface of solutions that were supersaturated with respect to calcite (initial Ω = 20, where Ω = 1 represents saturation), thereby leading to the continuous nucleation and growth of calcite crystals. Lognormal CSDs resulted when reactants were added continuously below the solution surface, via a submerged tube, to similarly supersaturated solutions (initial Ω = 22 to 41), thereby leading to a single nucleation event followed by surface-controlled growth. The Ostwald CSD resulted when concentrated reactants were rapidly mixed, leading initially to high levels of supersaturation (Ω >100), and to the formation and subsequent dissolution of very small nuclei, thereby yielding CSDs having small crystal size variances. The three CSD shapes likely were produced early in the crystallization process, in the nanometer crystal size range, and preserved during subsequent growth. Preservation of the relative shapes of the CSDs indicates that a supply-controlled growth mechanism

  17. Geobacillus thermoglucosidasius Endospores Function as Nuclei for the Formation of Single Calcite Crystals

    PubMed Central

    Murai, Rie

    2013-01-01

    Geobacillus thermoglucosidasius colonies were placed on an agar hydrogel containing acetate, calcium ions, and magnesium ions, resulting in the formation of single calcite crystals (calcites) within and peripheral to the plating area or parent colony. Microscopic observation of purified calcites placed on the surface of soybean casein digest (SCD) nutrient medium revealed interior crevices from which bacterial colonies originated. Calcites formed on the gel contained [1-13C]- and [2-13C]acetate, demonstrating that G. thermoglucosidasius utilizes carbon derived from acetate for calcite formation. During calcite formation, vegetative cells swam away from the parent colony in the hydrogel. Hard-agar hydrogel inhibited the formation of calcites peripheral to the parent colony. The calcite dissolved completely in 1 M HCl, with production of bubbles, and the remaining endospore-like particles were easily stained with Brilliant green dye. The presence of DNA and protein in calcites was demonstrated by electrophoresis. We propose that endospores initiate the nucleation of calcites. Endospores of G. thermoglucosidasius remain alive and encapsulated in calcites. PMID:23455343

  18. Effects of chitosan on the alignment, morphology and shape of calcite crystals nucleating under Langmuir monolayers

    SciTech Connect

    Kim, Kyungil; Uysal, Ahmet; Kewalramani, Sumit; Stripe, Benjamin; Dutta, Pulak

    2009-04-22

    The growth of calcium carbonate crystals under Langmuir monolayers was investigated in the presence of chitosan, a soluble derivative of chitin added to the subphase to better simulate the polyelectrolyte-containing in vivo environment. Chitosan causes distinct concentration-dependent changes in the orientation, shape and morphology of the calcite crystals nucleating under acid and sulfate monolayers. Our results suggest that polyelectrolytes may play essential roles in controlling the growth of biogenic calcite crystals.

  19. Effects of Chitosan on the Morphology and Alignment of Calcite Crystals Nucleating Under Langmuir Monolayers

    SciTech Connect

    Kim, K.; Uysal, A; Kewalramani, S; Stripe, B; Dutta, P

    2009-01-01

    The growth of calcium carbonate crystals under Langmuir monolayers was investigated in the presence of chitosan, a soluble derivative of chitin added to the subphase to better simulate the polyelectrolyte-containing in vivo environment. Chitosan causes distinct concentration-dependent changes in the orientation, shape and morphology of the calcite crystals nucleating under acid and sulfate monolayers. Our results suggest that polyelectrolytes may play essential roles in controlling the growth of biogenic calcite crystals.

  20. Origin of platy calcite crystals in hot-spring deposits in the Kenya Rift Valley

    SciTech Connect

    Jones, B.; Renault, R.W.

    1998-09-01

    Platy calcite crystals, which have their c axis parallel to their shortest length axis, are common components of travertine deposits found around some hot springs in the Kenya Rift Valley. They are composite crystals formed of numerous paper-thin subcrystals. Individual plates allowed to grow without obstruction develop a hexagonal motif. The Kenyan crystals typically form in hot (>75 C) waters that have a low Ca content (<10 mg/l), a high CO{sub 2} content, and a high rate of CO{sub 2} degassing. At Chemurkeu, aggregates of numerous small platy crystals collectively form lattice crystals that superficially resemble ray crystals. The walls of the lattice crystals are formed of large platy crystals that have their long and intermediate length axes aligned parallel to the plane of the long axis of the lattice crystal. Internally, the lattice crystals are formed of small platy calcite crystals arranged in a boxlike pattern that creates the appearance of a lattice when viewed in thin section. Lattice crystals are highly porous, with each pore being enclosed by platy crystals. At Lorusio, travertines are mainly formed of pseudodentrites that are constructed by numerous small platy crystals attached to a main stem which is a large platy crystal that commonly curves along its long axis. The pseudodentrites are the main construction blocks in ledges and lilypads that form in the vent pool and spring outflow channels, where the water is too hot for microbes other than hyperthermophiles. The platy calcite crystals in the Kenyan travertines are morphologically similar to platy calcite crystals that form as scale in pipes in the geothermal fields of New Zealand and hydrothermal angel wing calcite from the La Fe mine in Mexico. Comparison of the Kenyan and New Zealand crystals indicates that platy calcite crystals form from waters with a low Ca{sup 2+} content and a high CO{sub 3}/Ca ratio due to rapid rates of CO{sub 2} degassing.

  1. Initial formation of calcite crystals in the thin prismatic layer with the periostracum of Pinctada fucata.

    PubMed

    Suzuki, Michio; Nakayama, Seiji; Nagasawa, Hiromichi; Kogure, Toshihiro

    2013-02-01

    Although the formation mechanism of calcite crystals in the prismatic layer has been studied well in many previous works, the initial state of calcite formation has not been observed in detail using electron microscopes. In this study, we report that the soft prismatic layer with transparent color (the thin prismatic layer) in the tip of the fresh shell of Pinctada fucata was picked up to observe the early calcification phase. A scanning electron microscope (SEM) image showed that the growth tip of the thin prismatic layer was covered by the periostracum, which was also where the initial formation of calcite crystals began. A cross-section containing the thin calcite crystals in the thin prismatic layer with the periostracum was made using a focused ion beam (FIB) system. In a transmission electron microscope (TEM) observation, the thin calcite crystal (thickness is about 1μm) on the periostracum was found to be a single crystal with the c-axis oriented perpendicular to the shell surface. On the other hand, many aggregated small particles consisting of bassanite crystals were observed in the periostracum suggesting the possibility that not only organic sulfate but also inorganic sulfates exist in the prismatic layer. These discoveries in the early calcification phase of the thin prismatic layer may help to clarify the mechanism of regulating the nucleation and orientation of the calcite crystal in the shell.

  2. Morphological changes of calcite single crystals induced by graphene-biomolecule adducts

    NASA Astrophysics Data System (ADS)

    Calvaresi, Matteo; Di Giosia, Matteo; Ianiro, Alessandro; Valle, Francesco; Fermani, Simona; Polishchuk, Iryna; Pokroy, Boaz; Falini, Giuseppe

    2017-01-01

    Calcite has the capability to interact with a wide variety of molecules. This usually induces changes in shape and morphology of crystals. Here, this process was investigated using sheets of graphene-biomolecule adducts. They were prepared and made dispersible in water through the exfoliation of graphite by tip sonication in the presence tryptophan or N-acetyl-D-glucosamine. The crystallization of calcium carbonate in the presence of these additives was obtained by the vapor diffusion method and only calcite formed. The analysis of the microscopic observations showed that the graphene-biomolecule adducts affected shape and morphology of rhombohedral {10.4} faced calcite crystals, due to their stabilization of additional {hk.0} faces. The only presence of the biomolecule affected minimally shape and morphology of calcite crystals, highlighting the key role of the graphene sheets as 2D support for the adsorption of the biomolecules.

  3. Heterogeneous distribution of dye-labelled biomineralizaiton proteins in calcite crystals.

    PubMed

    Liu, Chuang; Xie, Liping; Zhang, Rongqing

    2015-12-17

    Biominerals are highly ordered crystals mediated by organic matters especially proteins in organisms. However, how specific proteins are distributed inside biominerals are not well understood. In the present study, we use fluorescein isothiocyanate (FITC) to label extracted proteins from the shells of bivalve Pinctada fucata. By confocal laser scanning microscopy (CLSM), we observe a heterogeneous distribution of dye-labelled proteins inside synthetic calcite at the microscale. Proteins from the prismatic calcite layers accumulate at the edge of crystals while proteins from the nacreous aragonite layers accumulate at the center of crystals. Raman and X-ray powder diffraction show that both the proteins cannot alter the crystal phase. Scanning electron microscope demonstrates both proteins are able to affect the crystal morphology. This study may provide a direct approach for the visualization of protein distributions in crystals by small-molecule dye-labelled proteins as the additives in the crystallization process and improve our understanding of intracrystalline proteins distribution in biogenic calcites.

  4. Rotation rate measurement and calculation for calcite crystals in a C-point mode

    NASA Astrophysics Data System (ADS)

    Herne, Catherine M.; O'Brien, Ann E.

    2016-09-01

    A polarization singularity mode offers a unique tool for actuating an array of birefringent calcite crystals, and measurement of the rotation rates of these crystals is in turn a way to image modes with varying polarization. In this work, we show the calculated and measured rotation rates of individual calcite crystals in a C-point mode and their dependence on three key factors: polarization, mode intensity profile, and crystal size. The C-point is a polarization singularity mode in which the mode has a circularly polarized center surrounded by elliptically polarized regions, with the orientation of the ellipse varying azimuthally and the degree of ellipticity changing radially. The beam is focused into an optical trapping region, and micron-sized birefringent calcite crystals in solution are positioned at key points in the mode. The crystals experience different torques at each location. The spin angular momentum of the light is proportional to the degree of ellipticity and to the intensity at each point in the mode. Our technique for generating C-point modes results in an intensity profile with a nonlinear radial dependence. Our crystal growth process generates crystals of varying width and thickness; the crystal size and shape affect the drag forces and light torque acting on them. We explain the crystal growth process and estimations of torque, demonstrate the rate and direction of rotation of calcite crystals placed at different points in the laser mode, and discuss the difference between the estimated and measured rotation rates.

  5. Lattice distortions in coccolith calcite crystals originate from occlusion of biomacromolecules.

    PubMed

    Hood, Matthew A; Leemreize, Hanna; Scheffel, André; Faivre, Damien

    2016-11-01

    During biomineralization, organisms control the formation and morphology of a mineral using biomacromolecules. The biomacromolecules that most strongly interact with the growing crystals frequently get occluded within. Such an observation has been recently obtained for the calcium carbonate producing coccolithophore species Pleurochrysis carterae. Coccolithophores are unicellular algae that produce calcified scales built from complex-shaped calcite crystals, termed coccoliths. It is unclear how widespread the phenomenon of biomacromolecular occlusion within calcite crystals is in calcifying haptophytes such as coccolithophores. Here, the coccoliths of biological replicates of the bloom forming Emiliania huxleyi are compared with that of Pleurochrysis carterae, two species with different coccolith morphologies and crystal growth mechanisms. From high-resolution synchrotron X-ray diffraction, changes in the lattice parameters of coccolith calcite, after heating to 450°C, are observed and associated with macrostrain originating from occluded biomacromolecules. We propose a mechanism governing the biomacromolecules' interaction with the growing coccolith crystals and their likely origin.

  6. Capillarity creates single-crystal calcite nanowires from amorphous calcium carbonate.

    PubMed

    Kim, Yi-Yeoun; Hetherington, Nicola B J; Noel, Elizabeth H; Kröger, Roland; Charnock, John M; Christenson, Hugo K; Meldrum, Fiona C

    2011-12-23

    Single-crystal calcite nanowires are formed by crystallization of morphologically equivalent amorphous calcium carbonate (ACC) particles within the pores of track etch membranes. The polyaspartic acid stabilized ACC is drawn into the membrane pores by capillary action, and the single-crystal nature of the nanowires is attributed to the limited contact of the intramembrane ACC particle with the bulk solution. The reaction environment then supports transformation to a single-crystal product.

  7. Morphological and mechanical characterization of composite calcite/SWCNT-COOH single crystals.

    PubMed

    Calvaresi, Matteo; Falini, Giuseppe; Pasquini, Luca; Reggi, Michela; Fermani, Simona; Gazzadi, Gian Carlo; Frabboni, Stefano; Zerbetto, Francesco

    2013-08-07

    A growing number of classes of organic (macro)molecular materials have been trapped into inorganic crystalline hosts, such as calcite single crystals, without significantly disrupting their crystalline lattices. Inclusion of an organic phase plays a key role in enhancing the mechanical properties of the crystals, which are believed to share structural features with biogenic minerals. Here we report the synthesis and mechanical characterization of composite calcite/SWCNT-COOH single crystals. Once entrapped into the crystals SWCNT-COOH appeared both as aggregates of entangled bundles and nanoropes. Their observation was possible only after crystal etching, fracture or FIB (focused ion beam) cross-sectioning. SWCNT-COOHs occupied a small volume fraction and were randomly distributed into the host crystal. They did not strongly affect the crystal morphology. However, although the Young's modulus of composite calcite/SWCNT-COOH single crystals was similar to that of pure calcite their hardness increased by about 20%. Thus, SWCNT-COOHs provide an obstacle against the dislocation-mediated propagation of plastic deformation in the crystalline slip systems, in analogy with the well-known hardness increase in fiber-reinforced composites.

  8. Amelogenin processing by MMP-20 prevents protein occlusion inside calcite crystals

    PubMed Central

    Bromley, Keith M.; Lakshminarayanan, Rajamani; Thompson, Mitchell; Lokappa, Sowmya B.; Gallon, Victoria A.; Cho, Kang R.; Qiu, S. Roger; Moradian-Oldak, Janet

    2012-01-01

    Calcite crystals were grown in the presence of full-length amelogenin and during its proteolysis by recombinant human matrix metalloproteinase 20 (rhMMP-20). Recombinant porcine amelogenin (rP172) altered the shape of calcite crystals by inhibiting the growth of steps on the {104} faces and became occluded inside the crystals. Upon co-addition of rhMMP-20, the majority of the protein was digested resulting in a truncated amelogenin lacking the C-terminal segment. In rP172-rhMMP-20 samples, the occlusion of amelogenin into the calcite crystals was drastically decreased. Truncated amelogenin (rP147) and the 25-residue C-terminal domain produced crystals with regular shape and less occluded organic material. Removal of the C-terminal diminished the affinity of amelogenin to the crystals and therefore prevented occlusion. We hypothesize that HAP and calcite interact with amelogenin in a similar manner. In the case of each material, full-length amelogenin binds most strongly, truncated amelogenin binds weakly and the C-terminus alone has the weakest interaction. Regarding enamel crystal growth, the prevention of occlusion into maturing enamel crystals might be a major benefit resulting from the selective cleavage of amelogenin at the C-terminus by MMP-20. Our data have important implications for understanding the hypomineralized enamel phenotype in cases of amelogenesis imperfecta resulting from MMP-20 mutations and will contribute to the design of enamel inspired biomaterials. PMID:23226976

  9. The kinetics and mechanisms of amorphous calcium carbonate (ACC) crystallization to calcite, via vaterite.

    PubMed

    Rodriguez-Blanco, Juan Diego; Shaw, Samuel; Benning, Liane G

    2011-01-01

    The kinetics and mechanisms of nanoparticulate amorphous calcium carbonate (ACC) crystallization to calcite, via vaterite, were studied at a range of environmentally relevant temperatures (7.5-25 °C) using synchrotron-based in situ time-resolved Energy Dispersive X-ray Diffraction (ED-XRD) in conjunction with high-resolution electron microscopy, ex situ X-ray diffraction and infrared spectroscopy. The crystallization process occurs in two stages; firstly, the particles of ACC rapidly dehydrate and crystallize to form individual particles of vaterite; secondly, the vaterite transforms to calcite via a dissolution and reprecipitation mechanism with the reaction rate controlled by the surface area of calcite. The second stage of the reaction is approximately 10 times slower than the first. Activation energies of calcite nucleation and crystallization are 73±10 and 66±2 kJ mol(-1), respectively. A model to calculate the degree of calcite crystallization from ACC at environmentally relevant temperatures (7.5-40 °C) is also presented.

  10. Strain-relief by single dislocation loops in calcite crystals grown on self-assembled monolayers

    SciTech Connect

    Ihli, Johannes; Clark, Jesse N.; Côté, Alexander S.; Kim, Yi-Yeoun; Schenk, Anna S.; Kulak, Alexander N.; Comyn, Timothy P.; Chammas, Oliver; Harder, Ross J.; Duffy, Dorothy M.; Robinson, Ian K.; Meldrum, Fiona C.

    2016-06-15

    Most of our knowledge of dislocation-mediated stress relaxation during epitaxial crystal growth comes from the study of inorganic heterostructures. In this study, we use Bragg coherent diffraction imaging to investigate a contrasting system, the epitaxial growth of calcite (CaCO3) crystals on organic self-assembled monolayers, where these are widely used as a model for biomineralization processes. The calcite crystals are imaged to simultaneously visualize the crystal morphology and internal strain fields. Our data reveal that each crystal possesses a single dislocation loop that occupies a common position in every crystal. The loops exhibit entirely different geometries to misfit dislocations generated in conventional epitaxial thin films and are suggested to form in response to the stress field, arising from interfacial defects and the nanoscale roughness of the substrate. In conclusion, this work provides unique insight into how self-assembled monolayers control the growth of inorganic crystals and demonstrates important differences as compared with inorganic substrates.

  11. Strain-relief by single dislocation loops in calcite crystals grown on self-assembled monolayers

    PubMed Central

    Ihli, Johannes; Clark, Jesse N.; Côté, Alexander S.; Kim, Yi-Yeoun; Schenk, Anna S.; Kulak, Alexander N.; Comyn, Timothy P.; Chammas, Oliver; Harder, Ross J.; Duffy, Dorothy M.; Robinson, Ian K.; Meldrum, Fiona C.

    2016-01-01

    Most of our knowledge of dislocation-mediated stress relaxation during epitaxial crystal growth comes from the study of inorganic heterostructures. Here we use Bragg coherent diffraction imaging to investigate a contrasting system, the epitaxial growth of calcite (CaCO3) crystals on organic self-assembled monolayers, where these are widely used as a model for biomineralization processes. The calcite crystals are imaged to simultaneously visualize the crystal morphology and internal strain fields. Our data reveal that each crystal possesses a single dislocation loop that occupies a common position in every crystal. The loops exhibit entirely different geometries to misfit dislocations generated in conventional epitaxial thin films and are suggested to form in response to the stress field, arising from interfacial defects and the nanoscale roughness of the substrate. This work provides unique insight into how self-assembled monolayers control the growth of inorganic crystals and demonstrates important differences as compared with inorganic substrates. PMID:27302863

  12. Control of macromolecule distribution within synthetic and biogenic single calcite crystals

    SciTech Connect

    Aizenberg, J.; Weiner, S.; Addadi, L.; Hanson, J.; Koetzle, T.F.

    1997-02-05

    The ability of organisms to exercise control over crystal growth is wonderfully exemplified by skeleton formation in echinoderms. A sea urchin spine is a unique composite of a single crystal of calcite and glycoproteins intercalated inside the crystal during its growth. Here we performed a detailed morphological and high-resolution synchrotron X-ray diffraction study of the textures of synthetic and biogenic calcite crystals. We show that the intracrystalline macromolecules from sea urchin spines, when allowed to interact with growing calcite crystals in vitro, selectively reduce the coherence lengths and degrees of alignment of the perfect domains in specific crystallographic directions. These directions also correspond to the newly-developed stable faces. In contrast, the defect distribution of young sea urchin spines composed entirely of spongy stereomic structure is much more isotropic. In mature spines containing secondarily filled-in wedges of calcite, the degree of anisotropy is intermediate between that of the synthetic crystals and the young spines. The macromolecules extracted from young and mature spines are, however, very similar. These observations demonstrate the inherent capability of occluded matrix macromolecules to finely differentiate between crystal planes by stereochemical recognition processes. 20 refs., 5 figs., 2 tabs.

  13. Surrogate Seeds For Growth Of Crystals

    NASA Technical Reports Server (NTRS)

    Shlichta, Paul J.

    1989-01-01

    Larger crystals of higher quality grown. Alternative method for starting growth of crystal involves use of seed crystal of different material instead of same material as solution. Intended for growing single-crystal proteins for experiments but applicable in general to growth of crystals from solutions and to growth of semiconductor or other crystals from melts.

  14. Crystallization of ikaite and its pseudomorphic transformation into calcite: Raman spectroscopy evidence

    NASA Astrophysics Data System (ADS)

    Sánchez-Pastor, N.; Oehlerich, Markus; Astilleros, José Manuel; Kaliwoda, Melanie; Mayr, Christoph C.; Fernández-Díaz, Lurdes; Schmahl, Wolfgang W.

    2016-02-01

    Ikaite (CaCO3·6H2O) is a metastable phase that crystallizes in nature from alkaline waters with high phosphate concentrations at temperatures close to 0 °C. This mineral transforms into anhydrous calcium carbonate polymorphs when temperatures rise or when exposed to atmospheric conditions. During the transformation in some cases the shape of the original ikaite crystal is preserved as a pseudomorph. Pseudomorphs after ikaite are considered as a valuable paleoclimatic indicator. In this work we conducted ikaite crystal growth experiments at near-freezing temperatures using the single diffusion silica gel technique, prepared with a natural aqueous solution from the polymictic lake Laguna Potrok Aike (51°57‧S, 70°23‧W) in Patagonia, Argentina. The ikaite crystals were recovered from the gels and the transformation reactions were monitored by in situ Raman spectroscopy at two different temperatures. The first spectra collected showed the characteristic features of ikaite. In successive spectra new bands at 1072, 1081 and 1086 cm-1 and changes in the intensity of bands corresponding to the OH modes were observed. These changes in the Raman spectra were interpreted as corresponding to intermediate stages of the transformation of ikaite into calcite and/or vaterite. After a few hours, the characteristics of the Raman spectrum were consistent with those of calcite. While ikaite directly transforms into calcite at 10 °C in contact with air, at 20 °C this transformation involves the formation of intermediate, metastable vaterite. During the whole process the external shape of ikaite crystals was preserved. Therefore, this transformation showed the typical characteristics of a pseudomorphic mineral replacement, involving the generation of a large amount of porosity to account for the large difference in molar volumes between ikaite and calcite. A mechanism involving the coupled dissolution of ikaite and crystallization of calcite/vaterite is proposed for this

  15. Heterogeneous distribution of dye-labelled biomineralizaiton proteins in calcite crystals

    PubMed Central

    Liu, Chuang; Xie, Liping; Zhang, Rongqing

    2015-01-01

    Biominerals are highly ordered crystals mediated by organic matters especially proteins in organisms. However, how specific proteins are distributed inside biominerals are not well understood. In the present study, we use fluorescein isothiocyanate (FITC) to label extracted proteins from the shells of bivalve Pinctada fucata. By confocal laser scanning microscopy (CLSM), we observe a heterogeneous distribution of dye-labelled proteins inside synthetic calcite at the microscale. Proteins from the prismatic calcite layers accumulate at the edge of crystals while proteins from the nacreous aragonite layers accumulate at the center of crystals. Raman and X-ray powder diffraction show that both the proteins cannot alter the crystal phase. Scanning electron microscope demonstrates both proteins are able to affect the crystal morphology. This study may provide a direct approach for the visualization of protein distributions in crystals by small-molecule dye-labelled proteins as the additives in the crystallization process and improve our understanding of intracrystalline proteins distribution in biogenic calcites. PMID:26675363

  16. Observation of an Organic-Inorganic Lattice Match during Biomimetic Growth of (001)-Oriented Calcite Crystals under Floating Sulfate Monolayers

    SciTech Connect

    Kewalramani, S.; Kim, K; Stripe, B; Evmenenko, G; Dommett, G; Dutta, P

    2008-01-01

    Macromolecular layers rich in amino acids and with some sulfated polysaccharides appear to control oriented calcite growth in living organisms. Calcite crystals nucleating under floating acid monolayers have been found to be unoriented on average. We have now observed directly, using in situ grazing incidence X-ray diffraction, that there is a 1:1 match between the monolayer unit cell and the unit cell of the (001) plane of calcite. Thus, sulfate head groups appear to act as templates for the growth of (001)-oriented calcite crystals, which is the orientation commonly found in biominerals.

  17. Transformation of amorphous calcium carbonate to rod-like single crystal calcite via "copying" collagen template.

    PubMed

    Xue, Zhonghui; Hu, Binbin; Dai, Shuxi; Du, Zuliang

    2015-10-01

    Collagen Langmuir films were prepared by spreading the solution of collagen over deionized water, CaCl2 solution and Ca(HCO3)2 solution. Resultant collagen Langmuir monolayers were then compressed to a lateral pressure of 10 mN/m and held there for different duration, allowing the crystallization of CaCO3. The effect of crystallization time on the phase composition and microstructure of CaCO3 was investigated. It was found that amorphous calcium carbonate (ACC) was obtained at a crystallization time of 6 h. The amorphous CaCO3 was transformed to rod-like single crystal calcite crystals at an extended crystallization time of 12 h and 24 h, via "copying" the symmetry and dimensionalities of collagen fibers. Resultant calcite crystallites were well oriented along the longitudinal axis of collagen fibers. The ordered surface structure of collagen fibers and electrostatic interactions played key roles in tuning the oriented nucleation and growth of the calcite crystallites. The mineralized collagen possessing both desired mechanical properties of collagen fiber and good biocompatibility of calcium carbonate may be assembled into an ideal biomaterial for bone implants.

  18. Swift heavy ion irradiation induced phase transformation in calcite single crystals

    NASA Astrophysics Data System (ADS)

    Nagabhushana, H.; Nagabhushana, B. M.; Lakshminarasappa, B. N.; Singh, Fouran; Chakradhar, R. P. S.

    2009-11-01

    Ion irradiation induced phase transformation in calcite single crystals have been studied by means of Raman and infrared spectroscopy using 120 MeV Au 9+ ions. The observed bands have been assigned according to group theory analysis. For higher fluence of 5×10 12 ion/cm 2, an extra peak on either side of the 713 cm -1 peak and an increase in the intensity of 1085 cm -1 peak were observed in Raman studies. FTIR spectra exhibit extra absorption bands at 674, 1589 cm -1 and enhancement in bands at 2340 and 2374 cm -1 was observed. This might be due to the phase transformation from calcite to vaterite. The damage cross section ( σ) for all the Raman and FTIR active modes was determined. The increase of FWHM, shift in peak positions and appearance of new peaks indicated that calcite phase is converted into vaterite.

  19. Influence of Bacillus subtilis cell walls and EDTA on calcite dissolution rates and crystal surface features.

    PubMed

    Friis, A K; Davis, T A; Figueira, M M; Paquette, J; Mucci, A

    2003-06-01

    This study investigates the influence of EDTA and the Gram-positive cell walls of Bacillus subtilis on the dissolution rates and development of morphological features on the calcite [1014] surface. The calcite dissolution rates are compared at equivalent saturation indicies (SI) and relative to its dissolution behavior in distilled water (DW). Results indicate that the presence of metabolically inactive B. subtilis does not affect the dissolution rates significantly. Apparent increases in dissolution rates in the presence of the dead bacterial cells can be accounted for by a decrease of the saturation state of the solution with respect to calcite resulting from bonding of dissolved Ca2+ by functional groups on the cell walls. In contrast, the addition of EDTA to the experimental solutions results in a distinct increase in dissolution rates relative to those measured in DW and the bacterial cell suspensions. These results are partly explained by the 6.5-8 orders of magnitude greater stability of the Ca-EDTA complex relative to the Ca-B. subtilis complexes as well as its free diffusion to and direct attack of the calcite surface. Atomic force microscopy images of the [1014] surface of calcite crystals exposed to our experimental solutions reveal the development of dissolution pits with different morphologies according to the nature and concentration of the ligand. Highly anisotropic dissolution pits develop in the early stages of the dissolution reaction at low B. subtilis concentrations (0.004 mM functional group sites) and in DW. In contrast, at high functional group concentrations (4.0 mM EDTA or equivalent B. subtilis functional group sites), dissolution pits are more isotropic. These results suggest that the mechanism of calcite dissolution is modified by the presence of high concentrations of organic ligands. Since all the pits that developed on the calcite surfaces display some degree of anisotropy and dissolution rates are strongly SI dependent, the rate

  20. Nanobacteria-like calcite single crystals at the surface of the Tataouine meteorite.

    PubMed

    Benzerara, Karim; Menguy, Nicolas; Guyot, Francois; Dominici, Christian; Gillet, Philippe

    2003-06-24

    Nanobacteria-like objects evidenced at the surface of the orthopyroxenes of the Tataouine meteorite in South Tunisia have been studied by scanning and transmission electron microscopies. A method of micromanipulation has been developed to ensure that exactly the same objects were studied by both methods. We have shown that the nanobacteria-like objects are spatially correlated with filaments of microorganisms that colonized the surface of the meteoritic pyroxene during its 70 years of residence in the aridic Tataouine soil. Depressions of a few micrometers in depth are observed in the pyroxene below the carbonates, indicating preferential dissolution of the pyroxene and calcite precipitation at these locations. The nanobacteria-like small rods that constitute calcium carbonate rosettes are well crystallized calcite single crystals surrounded by a thin amorphous layer of carbonate composition that smoothes the crystal edges and induces rounded shapes. Those morphologies are unusual for calcite single crystals observed in natural samples. A survey of recent literature suggests that the intervention of organic compounds derived from biological activity is likely in their formation.

  1. Morphology of calcite crystals in clast coatings from four soils in the Mojave desert region

    NASA Technical Reports Server (NTRS)

    Chadwick, Oliver A.; Sowers, Janet M.; Amundson, Ronald G.

    1989-01-01

    Pedogenic calcite-crystal coatings on clasts were examined in four soils along an altitudinal gradient on Kyle Canyon alluvium in southern Nevada. Clast coatings were studied rather than matrix carbonate to avoid the effects of soil matrix on crystallization. Six crystal sizes and shapes were recognized and distinguished. Equant micrite was the dominant crystal form with similar abundance at all elevations. The distributions of five categories of spar and microspar appear to be influenced by altitudinally induced changes in effective moisture. In the drier, lower elevation soils, crystals were equant or parallel prismatic with irregular, interlocking boundaries while in the more moist, higher elevation soils they were randomly oriented, euhedral, prismatic, and fibrous. There was little support for the supposition that Mg(+2) substitution or increased (Mg + Ca)/HCO3 ratios in the precipitating solution produced crystal elongation.

  2. The effect of fluid composition, salinity, and acidity on subcritical crack growth in calcite crystals

    NASA Astrophysics Data System (ADS)

    Bergsaker, Anne Schad; Røyne, Anja; Ougier-Simonin, Audrey; Aubry, Jérôme; Renard, François

    2016-03-01

    Chemically activated processes of subcritical cracking in calcite control the time-dependent strength of this mineral, which is a major constituent of the Earth's brittle upper crust. Here experimental data on subcritical crack growth are acquired with a double torsion apparatus to characterize the influence of fluid pH (range 5-7.5) and ionic strength and species (Na2SO4, NaCl, MgSO4, and MgCl2) on the propagation of microcracks in calcite single crystals. The effect of different ions on crack healing has also been investigated by decreasing the load on the crack for durations up to 30 min and allowing it to relax and close. All solutions were saturated with CaCO3. The crack velocities reached during the experiments are in the range 10-9-10-2 m/s and cover the range of subcritical to close to dynamic rupture propagation velocities. Results show that for calcite saturated solutions, the energy necessary to fracture calcite is independent of pH. As a consequence, the effects of fluid salinity, measured through its ionic strength, or the variation of water activity have stronger effects on subcritical crack propagation in calcite than pH. Consequently, when considering the geological sequestration of CO2 into carbonate reservoirs, the decrease of pH within the range of 5-7.5 due to CO2 dissolution into water should not significantly alter the rate of fracturing of calcite. Increase in salinity caused by drying may lead to further reduction in cracking and consequently a decrease in brittle creep. The healing of cracks is found to vary with the specific ions present.

  3. Strain-relief by single dislocation loops in calcite crystals grown on self-assembled monolayers

    DOE PAGES

    Ihli, Johannes; Clark, Jesse N.; Côté, Alexander S.; ...

    2016-06-15

    Most of our knowledge of dislocation-mediated stress relaxation during epitaxial crystal growth comes from the study of inorganic heterostructures. In this study, we use Bragg coherent diffraction imaging to investigate a contrasting system, the epitaxial growth of calcite (CaCO3) crystals on organic self-assembled monolayers, where these are widely used as a model for biomineralization processes. The calcite crystals are imaged to simultaneously visualize the crystal morphology and internal strain fields. Our data reveal that each crystal possesses a single dislocation loop that occupies a common position in every crystal. The loops exhibit entirely different geometries to misfit dislocations generated inmore » conventional epitaxial thin films and are suggested to form in response to the stress field, arising from interfacial defects and the nanoscale roughness of the substrate. In conclusion, this work provides unique insight into how self-assembled monolayers control the growth of inorganic crystals and demonstrates important differences as compared with inorganic substrates.« less

  4. Calcite crystal growth inhibition by humic substances with emphasis on hydrophobic acids from the Florida Everglades

    NASA Astrophysics Data System (ADS)

    Hoch, A. R.; Reddy, M. M.; Aiken, G. R.

    2000-01-01

    The crystallization of calcium carbonate minerals plays an integral role in the water chemistry of terrestrial ecosystems. Humic substances, which are ubiquitous in natural waters, have been shown to reduce or inhibit calcite crystal growth in experiments. The purpose of this study is to quantify and understand the kinetic effects of hydrophobic organic acids isolated from the Florida Everglades and a fulvic acid from Lake Fryxell, Antarctica, on the crystal growth of calcite (CaCO 3). Highly reproducible calcite growth experiments were performed in a sealed reactor at constant pH, temperature, supersaturation (Ω = 4.5), P CO2 (10 -3.5atm), and ionic strength (0.1 M) with various concentrations of organic acids. Higher plant-derived aquatic hydrophobic acids from the Everglades were more effective growth inhibitors than microbially derived fulvic acid from Lake Fryxell. Organic acid aromaticity correlated strongly with growth inhibition. Molecular weight and heteroatom content correlated well with growth inhibition, whereas carboxyl content and aliphatic nature did not.

  5. Calcite crystal growth inhibition by humic substances with emphasis on hydrophobic acids from the Florida Everglades

    USGS Publications Warehouse

    Hoch, A.R.; Reddy, M.M.; Aiken, G.R.

    2000-01-01

    The crystallization of calcium carbonate minerals plays an integral role in the water chemistry of terrestrial ecosystems. Humic substances, which are ubiquitous in natural waters, have been shown to reduce or inhibit calcite crystal growth in experiments. The purpose of this study is to quantify and understand the kinetic effects of hydrophobic organic acids isolated from the Florida Everglades and a fulvic acid from Lake Fryxell, Antarctica, on the crystal growth of calcite (CaCO3). Highly reproducible calcite growth experiments were performed in a sealed reactor at constant pH, temperature, supersaturation (?? = 4.5), P(CO2) (10-3.5atm), and ionic strength (0.1 M) with various concentrations of organic acids. Higher plant-derived aquatic hydrophobic acids from the Everglades were more effective growth inhibitors than microbially derived fulvic acid from Lake Fryxell. Organic acid aromaticity correlated strongly with growth inhibition. Molecular weight and heteroatom content correlated well with growth inhibition, whereas carboxyl content and aliphatic nature did not. Copyright (C) 1999 Elsevier Science Ltd.

  6. Shaping calcite crystals by means of comb polyelectrolytes having neutral hydrophilic teeth.

    PubMed

    Malferrari, Danilo; Fermani, Simona; Galletti, Paola; Goisis, Marco; Tagliavini, Emilio; Falini, Giuseppe

    2013-02-12

    Comb polyelectrolytes (CPs) having neutral hydrophilic teeth, similar to double hydrophilic block copolymers, are a powerful tool to modify the chemical-physical properties of inorganic crystalline materials. One of their main applications is in concrete technology, where they work as superplasticizers, particle-dispersing agents. Here, CPs, having the same poly(acrylic acid) (PAA) backbone chain and differing in the grafting with methoxy poly(ethylene glycol) chains (MPEG) of two molecular weights, were used to investigate the influence of tooth chains in polymer aggregation and in control on morphology and aggregation of calcite particles. These polymers aggregate, forming interpolymer hydrogen bonds between carboxylic groups and ether oxygen functionalities. The presence of calcium ions in solution further enhances aggregation. Crystallization experiments of calcite in the presence of CPs show that the specificity of interactions between polymers and crystal planes and control on aggregation and size of particles is a function of the content and chain length of the MPEG in the PAA backbone. These parameters limit and can make specific the electrostatic interactions with ionic crystalline planes. Moreover, the mechanism of crystallization, classical or nonclassical, is addressed by the CP structure and concentration. These findings have implications in the understanding of the complex chemical processes associated to concrete superplasticizers action and in the study of the biomineralization processes, where biological comb polyelectrolytes, the acidic glycoproteins, govern formation of calcitic structures.

  7. Morphological tranformation of calcite crystal growth by prismatic "acidic" polypeptide sequences.

    SciTech Connect

    Kim, I; Giocondi, J L; Orme, C A; Collino, J; Evans, J S

    2007-02-13

    Many of the interesting mechanical and materials properties of the mollusk shell are thought to stem from the prismatic calcite crystal assemblies within this composite structure. It is now evident that proteins play a major role in the formation of these assemblies. Recently, a superfamily of 7 conserved prismatic layer-specific mollusk shell proteins, Asprich, were sequenced, and the 42 AA C-terminal sequence region of this protein superfamily was found to introduce surface voids or porosities on calcite crystals in vitro. Using AFM imaging techniques, we further investigate the effect that this 42 AA domain (Fragment-2) and its constituent subdomains, DEAD-17 and Acidic-2, have on the morphology and growth kinetics of calcite dislocation hillocks. We find that Fragment-2 adsorbs on terrace surfaces and pins acute steps, accelerates then decelerates the growth of obtuse steps, forms clusters and voids on terrace surfaces, and transforms calcite hillock morphology from a rhombohedral form to a rounded one. These results mirror yet are distinct from some of the earlier findings obtained for nacreous polypeptides. The subdomains Acidic-2 and DEAD-17 were found to accelerate then decelerate obtuse steps and induce oval rather than rounded hillock morphologies. Unlike DEAD-17, Acidic-2 does form clusters on terrace surfaces and exhibits stronger obtuse velocity inhibition effects than either DEAD-17 or Fragment-2. Interestingly, a 1:1 mixture of both subdomains induces an irregular polygonal morphology to hillocks, and exhibits the highest degree of acute step pinning and obtuse step velocity inhibition. This suggests that there is some interplay between subdomains within an intra (Fragment-2) or intermolecular (1:1 mixture) context, and sequence interplay phenomena may be employed by biomineralization proteins to exert net effects on crystal growth and morphology.

  8. In Vitro Calcite Crystal Morphology Is Modulated by Otoconial Proteins Otolin-1 and Otoconin-90

    PubMed Central

    Moreland, K. Trent; Hong, Mina; Lu, Wenfu; Rowley, Christopher W.; Ornitz, David M.; De Yoreo, James J.; Thalmann, Ruediger

    2014-01-01

    Otoconia are formed embryonically and are instrumental in detecting linear acceleration and gravity. Degeneration and fragmentation of otoconia in elderly patients leads to imbalance resulting in higher frequency of falls that are positively correlated with the incidence of bone fractures and death. In this work we investigate the roles otoconial proteins Otolin-1 and Otoconin 90 (OC90) perform in the formation of otoconia. We demonstrate by rotary shadowing and atomic force microscopy (AFM) experiments that Otolin-1 forms homomeric protein complexes and self-assembled networks supporting the hypothesis that Otolin-1 serves as a scaffold protein of otoconia. Our calcium carbonate crystal growth data demonstrate that Otolin-1 and OC90 modulate in vitro calcite crystal morphology but neither protein is sufficient to produce the shape of otoconia. Coadministration of these proteins produces synergistic effects on crystal morphology that contribute to morphology resembling otoconia. PMID:24748133

  9. Incorporating Diblock Copolymer Nanoparticles into Calcite Crystals: Do Anionic Carboxylate Groups Alone Ensure Efficient Occlusion?

    PubMed Central

    2016-01-01

    New spherical diblock copolymer nanoparticles were synthesized via RAFT aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA) at 70 °C and 20% w/w solids using either poly(carboxybetaine methacrylate) or poly(proline methacrylate) as the steric stabilizer block. Both of these stabilizers contain carboxylic acid groups, but poly(proline methacrylate) is anionic above pH 9.2, whereas poly(carboxybetaine methacrylate) has zwitterionic character at this pH. When calcite crystals are grown at an initial pH of 9.5 in the presence of these two types of nanoparticles, it is found that the anionic poly(proline methacrylate)-stabilized particles are occluded uniformly throughout the crystals (up to 6.8% by mass, 14.0% by volume). In contrast, the zwitterionic poly(carboxybetaine methacrylate)-stabilized particles show no signs of occlusion into calcite crystals grown under identical conditions. The presence of carboxylic acid groups alone therefore does not guarantee efficient occlusion: overall anionic character is an additional prerequisite. PMID:27042383

  10. Corrosion of calcite crystals by metal-rich mud in caves: Study case in Crovassa Ricchi in Argento Cave (SW Sardinia, Italy)

    NASA Astrophysics Data System (ADS)

    Gázquez, Fernando; Calaforra, José-María; Forti, Paolo; De Waele, Jo; Sanna, Laura; Rull, Fernando; Sanz, Aurelio

    2013-09-01

    Unusual orange ochre crusts were recently discovered in Crovassa Ricchi in Argento Cave (San Giovanni Mine, SW Sardinia). These speleothems appear covering the cave walls on hydrothermal calcite spars as well as filling widened spaces between calcite crystals. Planar crusts display geometrical forms following the boundaries between the calcite spars. EDX-SEM microanalyses reveal that these deposits comprise substances of Fe, Mn, Pb, Zn and O that occur as solid inclusions in pits on the surface of altered calcite microcrystals. Micro-Raman spectroscopy analyses suggest the presence of calcite and ferromanganese oxides with a low degree of crystallinity. The genetic mechanism proposed for these speleothems describes an initial stage of precipitation of euhedral calcite crystals from warm water under subaqueous conditions. The crystal surfaces were eroded and corroded by colder aggressive water that smoothed the surfaces of the crystals and slightly widened the spaces between calcite spars. Metal-rich mud coming from alteration of bedrock and ore bodies filled the cave, also penetrating along the spaces between the calcite spars. When the water table fell below the cave level, part of the sediments was eroded but the cave walls remained covered with metal-rich clayey sediments. Under aerobic conditions, metals - which were reduced in previous stages - oxidized to oxides, lowering the pH and thus the crystal surface and the calcite planes between the spars were corroded. Subsequently, the polymetallic crusts became harder through evaporation within the cave, "fossilizing" the products of this process within the planes between spars. Finally, the exposed calcite surfaces continued to be altered due to CO2 diffusion into condensation water, while the boundaries between crystals were preserved against corrosion thanks to the crust coating. As a result, the external crystal edges protrude by several centimeters from the current cave wall, while the crystal surfaces are

  11. Device for isolation of seed crystals during processing of solution

    DOEpatents

    Montgomery, K.E.; Zaitseva, N.P.; Deyoreo, J.J.; Vital, R.L.

    1999-05-18

    A device is described for isolation of seed crystals during processing of solutions. The device enables a seed crystal to be introduced into the solution without exposing the solution to contaminants or to sources of drying and cooling. The device constitutes a seed protector which allows the seed to be present in the growth solution during filtration and overheating operations while at the same time preventing the seed from being dissolved by the under saturated solution. When the solution processing has been completed and the solution cooled to near the saturation point, the seed protector is opened, exposing the seed to the solution and allowing growth to begin. 3 figs.

  12. Device for isolation of seed crystals during processing of solution

    DOEpatents

    Montgomery, Kenneth E.; Zaitseva, Natalia P.; Deyoreo, James J.; Vital, Russell L.

    1999-01-01

    A device for isolation of see crystals during processing of solutions. The device enables a seed crystal to be introduced into the solution without exposing the solution to contaminants or to sources of drying and cooling. The device constitutes a seed protector which allows the seed to be present in the growth solution during filtration and overheating operations while at the same time preventing the seed from being dissolved by the under saturated solution. When the solution processing has been completed and the solution cooled to near the saturation point, the seed protector is opened, exposing the seed to the solution and allowing growth to begin.

  13. Heterogeneous Crystallization on Pairs of Pre-Structured Seeds.

    PubMed

    Jungblut, Swetlana; Dellago, Christoph

    2016-09-01

    Studying the effects of small pre-structured seeds on the crystallization transition in an undercooled monodisperse Lennard-Jones fluid with transition interface path sampling combined with molecular dynamics simulations, we analyze the impact of the simultaneous presence of two seeds with various structures. In the presence of seeds with face- and body-centered cubic structures, we find that decreasing the seed-to-seed distance enhances the probability of the crystalline clusters formed on one of the seeds to grow beyond the critical size, thus, increasing the crystal nucleation rates. In contrast, when seeds have an icosahedral structure, the crystalline clusters form mostly in the bulk. The crystal nucleation rate, however, is also determined by the distance between the seeds with regular structure in which the lattice spacing is equal to the bulk lattice constant, pointing to a heterogeneous crystal nucleation that occurs away from the icosahedrally structured seeds. For slightly squeezed seeds, the effects of the presence of seeds with face- and body-centered cubic structures are reduced in comparison to the regular seeds, and we do not see any effect of the presence of the second seed for seeds with squeezed icosahedral structure.

  14. Heterogeneous Crystallization on Pairs of Pre-Structured Seeds

    PubMed Central

    2016-01-01

    Studying the effects of small pre-structured seeds on the crystallization transition in an undercooled monodisperse Lennard-Jones fluid with transition interface path sampling combined with molecular dynamics simulations, we analyze the impact of the simultaneous presence of two seeds with various structures. In the presence of seeds with face- and body-centered cubic structures, we find that decreasing the seed-to-seed distance enhances the probability of the crystalline clusters formed on one of the seeds to grow beyond the critical size, thus, increasing the crystal nucleation rates. In contrast, when seeds have an icosahedral structure, the crystalline clusters form mostly in the bulk. The crystal nucleation rate, however, is also determined by the distance between the seeds with regular structure in which the lattice spacing is equal to the bulk lattice constant, pointing to a heterogeneous crystal nucleation that occurs away from the icosahedrally structured seeds. For slightly squeezed seeds, the effects of the presence of seeds with face- and body-centered cubic structures are reduced in comparison to the regular seeds, and we do not see any effect of the presence of the second seed for seeds with squeezed icosahedral structure. PMID:27479875

  15. Ab initio study of single-crystalline and polycrystalline elastic properties of Mg-substituted calcite crystals.

    PubMed

    Zhu, L-F; Friák, M; Lymperakis, L; Titrian, H; Aydin, U; Janus, A M; Fabritius, H-O; Ziegler, A; Nikolov, S; Hemzalová, P; Raabe, D; Neugebauer, J

    2013-04-01

    We employ ab initio calculations and investigate the single-crystalline elastic properties of (Ca,Mg)CO3 crystals covering the whole range of concentrations from pure calcite CaCO3 to pure magnesite MgCO3. Studying different distributions of Ca and Mg atoms within 30-atom supercells, our theoretical results show that the energetically most favorable configurations are characterized by elastic constants that nearly monotonously increase with the Mg content. Based on the first principles-derived single-crystalline elastic anisotropy, the integral elastic response of (Ca,Mg)CO3 polycrystals is determined employing a mean-field self-consistent homogenization method. As in case of single-crystalline elastic properties, the computed polycrystalline elastic parameters sensitively depend on the chemical composition and show a significant stiffening impact of Mg atoms on calcite crystals in agreement with the experimental findings. Our analysis also shows that it is not advantageous to use a higher-scale two-phase mix of stoichiometric calcite and magnesite instead of substituting Ca atoms by Mg ones on the atomic scale. Such two-phase composites are not significantly thermodynamically favorable and do not provide any strong additional stiffening effect.

  16. Fibrous and helical calcite crystals induced by synthetic polypeptides containing o-phospho-L-serine and o-phospho-L-threonine.

    PubMed

    Hayashi, Shinya; Ohkawa, Kousaku; Suwa, Yukie; Sugawara, Tetsunori; Asami, Takahiro; Yamamoto, Hiroyuki

    2008-01-09

    The modification of CaCO(3) crystal growth by synthetic L-Ser(PO(3)H(2)) and L-Thr(PO(3)H(2)) containing polypeptides is described. The amino acids Gly, L-Glu, L-Asp, L-Ser, L-Ala, and L-Lys induced rhombohedral calcite with a rough surface. Dipeptides, Xaa-L-Ser(PO(3)H(2)) (Xaa = Gly, L-Glu, L-Asp, L-Ser, L-Ala and L-Lys) induced vaterite crystals in the lower [Ca(2+)]. On the other hand, L-Ser(PO(3)H(2))-containing polypeptides formed spherical vaterite and fibrous calcite. The characteristic helical calcite was found in the presence of copoly[L-Ser(PO(3)H(2))(75)L-Asp(25)] or poly[L-Ser(PO(3)H(2))(3)-L-Asp]. Fibrous calcite, spherical vaterite, and helical calcite crystals were subjected to XRD and EDX analysis. XRD revealed the specific faces of these crystals. EDX spectra and surface analysis visualized the localization of the polypeptides and CaCO(3) components. Together with TEM and SAED data, we propose hypothetical growth mechanisms for the fibrous and helical calcite crystals.

  17. Birefringence measurements in single crystal sapphire and calcite shocked along the a axis

    NASA Astrophysics Data System (ADS)

    Tear, Gareth R.; Chapman, David J.; Eakins, Daniel E.; Proud, William G.

    2017-01-01

    Calcite and sapphire were shock compressed along the <10 1 ¯0 > direction (a axis) in a plate impact configuration. Polarimetery and Photonic Doppler Velocimetery (PDV) were used to measure the change in birefringence with particle velocity in the shock direction. Results for sapphire agree well with linear photoelastic theory and current literature showing a linear relationship between birefringence and particle velocity up to 310 m s-1. A maximum change in birefringence of 5% was observed. Calcite however showed anomolous behaviour with no detectable change in birefringence (less than 0.1%) over the range of particle velocities studied (up to 75 m s-1).

  18. Controls on the precipitation of barite (BaSO 4) crystals in calcite travertine at Twitya Spring, a warm sulphur spring in Canada's Northwest Territories

    NASA Astrophysics Data System (ADS)

    Bonny, Sandy M.; Jones, Brian

    2008-01-01

    Twitya Spring discharges warm (24 °C), anoxic, sulphide-, calcium- (65 ppm) and barium- (≥ 0.78 ppm) rich spring water to a steep flow path that is inhabited by streamer and mat-forming microbes ( Thiothrix, Beggiatoa, Oscillatoria, Spirulina, diatoms, rod shaped bacteria). Oxidation and CO 2 degassing drive precipitation of elemental sulphur, barite, opaline silica, and calcite. A mound of travertine at the base of the flow path, dominantly composed of bedded barium-enriched crystallographic and noncrystallographic dendritic calcite crystals and calcite cements, hosts three types of barite crystals: type 1 (T1) intergrown tabular crystals that formed in solution, type 2 (T2) tabular and rhombic crystals that nucleated on calcite, and type 3 (T3) subhedral and anhedral microcrystals that nucleated on microbial cell surfaces and in microbial extracellular polymeric substances. The formation and distribution of T1, T2, and T3 barite in the Twitya Spring flow path are controlled by physiochemical gradients, calcite precipitation rates, and adsorption of barium to microbial biomass, all of which vary seasonally and episodically at Twitya Spring. The complex physiochemical and biological controls on barite formation at Twitya Spring both suggest that the classification of biogenic or inorganic sedimentary barite on the basis of crystal size and morphology may be oversimplified. There is also the potential that primary and authigenic barite crystals hosted in carbonates may yield information about the microbial ecology and ambient physiochemistry of their depositional environments.

  19. A novel acidic matrix protein, PfN44, stabilizes magnesium calcite to inhibit the crystallization of aragonite.

    PubMed

    Pan, Cong; Fang, Dong; Xu, Guangrui; Liang, Jian; Zhang, Guiyou; Wang, Hongzhong; Xie, Liping; Zhang, Rongqing

    2014-01-31

    Magnesium is widely used to control calcium carbonate deposition in the shell of pearl oysters. Matrix proteins in the shell are responsible for nucleation and growth of calcium carbonate crystals. However, there is no direct evidence supporting a connection between matrix proteins and magnesium. Here, we identified a novel acidic matrix protein named PfN44 that affected aragonite formation in the shell of the pearl oyster Pinctada fucata. Using immunogold labeling assays, we found PfN44 in both the nacreous and prismatic layers. In shell repair, PfN44 was repressed, whereas other matrix proteins were up-regulated. Disturbing the function of PfN44 by RNAi led to the deposition of porous nacreous tablets with overgrowth of crystals in the nacreous layer. By in vitro circular dichroism spectra and fluorescence quenching, we found that PfN44 bound to both calcium and magnesium with a stronger affinity for magnesium. During in vitro calcium carbonate crystallization and calcification of amorphous calcium carbonate, PfN44 regulated the magnesium content of crystalline carbonate polymorphs and stabilized magnesium calcite to inhibit aragonite deposition. Taken together, our results suggested that by stabilizing magnesium calcite to inhibit aragonite deposition, PfN44 participated in P. fucata shell formation. These observations extend our understanding of the connections between matrix proteins and magnesium.

  20. Realisation of four-wave mixing phase matching for frequency components at intracavity stimulated Raman scattering in a calcite crystal

    SciTech Connect

    Smetanin, Sergei N; Fedin, Aleksandr V; Shurygin, Anton S

    2013-06-30

    The possibilities of implementing four-wave mixing (FWM) phase matching at stimulated Raman scattering (SRS) in a birefringent SRS-active crystal placed in a cavity with highly reflecting mirrors have been theoretically and experimentally investigated. Phase-matching angles providing conditions for five types of phase matching are determined for a calcite crystal. These types are characterised by different combinations of polarisation directions for the interacting waves and ensure FWM generation of either an anti-Stokes wave or the second Stokes SRS component. In agreement with the calculation results, low-threshold generation of the second Stokes SRS component with a wavelength 0.602 {mu}m was observed at angles of incidence on a calcite crystal of 4.8 Degree-Sign and 18.2 Degree-Sign , under SRS pumping at a wavelength of 0.532 {mu}m. This generation is due to the FWM coupling of the first and second Stokes SRS components with the SRS-pump wave. (nonlinear optical phenomena)

  1. A Novel Acidic Matrix Protein, PfN44, Stabilizes Magnesium Calcite to Inhibit the Crystallization of Aragonite*

    PubMed Central

    Pan, Cong; Fang, Dong; Xu, Guangrui; Liang, Jian; Zhang, Guiyou; Wang, Hongzhong; Xie, Liping; Zhang, Rongqing

    2014-01-01

    Magnesium is widely used to control calcium carbonate deposition in the shell of pearl oysters. Matrix proteins in the shell are responsible for nucleation and growth of calcium carbonate crystals. However, there is no direct evidence supporting a connection between matrix proteins and magnesium. Here, we identified a novel acidic matrix protein named PfN44 that affected aragonite formation in the shell of the pearl oyster Pinctada fucata. Using immunogold labeling assays, we found PfN44 in both the nacreous and prismatic layers. In shell repair, PfN44 was repressed, whereas other matrix proteins were up-regulated. Disturbing the function of PfN44 by RNAi led to the deposition of porous nacreous tablets with overgrowth of crystals in the nacreous layer. By in vitro circular dichroism spectra and fluorescence quenching, we found that PfN44 bound to both calcium and magnesium with a stronger affinity for magnesium. During in vitro calcium carbonate crystallization and calcification of amorphous calcium carbonate, PfN44 regulated the magnesium content of crystalline carbonate polymorphs and stabilized magnesium calcite to inhibit aragonite deposition. Taken together, our results suggested that by stabilizing magnesium calcite to inhibit aragonite deposition, PfN44 participated in P. fucata shell formation. These observations extend our understanding of the connections between matrix proteins and magnesium. PMID:24302723

  2. Homoepitaxial meso- and microscale crystal co-orientation and organic matrix network structure in Mytilus edulis nacre and calcite.

    PubMed

    Griesshaber, Erika; Schmahl, Wolfgang W; Ubhi, Harbinder Singh; Huber, Julia; Nindiyasari, Fitriana; Maier, Bernd; Ziegler, Andreas

    2013-12-01

    New developments in high-resolution, low accelaration voltage electron backscatter diffraction (EBSD) enable us to resolve and quantify the co-orientation of nanocrystals constituting biological carbonate crystals with a scan step resolution of 125 nm. This allows the investigation of internal structures in carbonate tablets and tower biocrystals in the nacre of mollusc shells, and it provides details on the calcite-aragonite polymorph interface in bivalves. Within the aragonite tablets of Mytilus edulis nacre we find a mesoscale crystallographic mosaic structure with a misorientation distribution of 2° full width at half maximum. Selective etching techniques with critical point drying reveal an organic matrix network inside the nacre tablets. The size scales of the visible aragonite tablet subunits and nanoparticles correspond to those of the open pore system in the organic matrix network. We further observe by EBSD that crystal co-orientation spans over tablet boundaries and forms composite crystal units of up to 20 stacked co-oriented tablets (tower crystals). Statistical evaluation of the misorientation data gives a probability distribution of grain boundary misorientations with two maxima: a dominant peak for very-small-angle grain boundaries and a small maximum near 64°, the latter corresponding to {110} twinning orientations. However, the related twin boundaries are typically the membrane-lined {001} flat faces of the tablets and not {110} twin walls within tablets. We attribute this specific pattern of misorientation distribution to growth by particle accretion and subsequent semicoherent homoepitaxial crystallization. The semicoherent crystallization percolates between the tablets through mineral bridges and across matrix membranes surrounding the tablets. In the "prismatic" calcite layer crystallographic co-orientation of the prisms reaches over more than 50 micrometers.

  3. Adjustment errors of sunstones in the first step of sky-polarimetric Viking navigation: studies with dichroic cordierite/ tourmaline and birefringent calcite crystals

    PubMed Central

    Száz, Dénes; Farkas, Alexandra; Blahó, Miklós; Barta, András; Egri, Ádám; Kretzer, Balázs; Hegedüs, Tibor; Jäger, Zoltán; Horváth, Gábor

    2016-01-01

    According to an old but still unproven theory, Viking navigators analysed the skylight polarization with dichroic cordierite or tourmaline, or birefringent calcite sunstones in cloudy/foggy weather. Combining these sunstones with their sun-dial, they could determine the position of the occluded sun, from which the geographical northern direction could be guessed. In psychophysical laboratory experiments, we studied the accuracy of the first step of this sky-polarimetric Viking navigation. We measured the adjustment error e of rotatable cordierite, tourmaline and calcite crystals when the task was to determine the direction of polarization of white light as a function of the degree of linear polarization p. From the obtained error functions e(p), the thresholds p* above which the first step can still function (i.e. when the intensity change seen through the rotating analyser can be sensed) were derived. Cordierite is about twice as reliable as tourmaline. Calcite sunstones have smaller adjustment errors if the navigator looks for that orientation of the crystal where the intensity difference between the two spots seen in the crystal is maximal, rather than minimal. For higher p (greater than pcrit) of incident light, the adjustment errors of calcite are larger than those of the dichroic cordierite (pcrit=20%) and tourmaline (pcrit=45%), while for lower p (less than pcrit) calcite usually has lower adjustment errors than dichroic sunstones. We showed that real calcite crystals are not as ideal sunstones as it was believed earlier, because they usually contain scratches, impurities and crystal defects which increase considerably their adjustment errors. Thus, cordierite and tourmaline can also be at least as good sunstones as calcite. Using the psychophysical e(p) functions and the patterns of the degree of skylight polarization measured by full-sky imaging polarimetry, we computed how accurately the northern direction can be determined with the use of the Viking sun

  4. High surface area calcite

    NASA Astrophysics Data System (ADS)

    Schultz, L. N.; Andersson, M. P.; Dalby, K. N.; Müter, D.; Okhrimenko, D. V.; Fordsmand, H.; Stipp, S. L. S.

    2013-05-01

    Calcite (CaCO3) is important in many fields—in nature, because it is a component of aquifers, oil reservoirs and prospective CO2 storage sites, and in industry, where it is used in products as diverse as paper, toothpaste, paint, plastic and aspirin. It is difficult to obtain high purity calcite with a high surface area but such material is necessary for industrial applications and for fundamental calcite research. Commercial powder is nearly always contaminated with growth inhibitors such as sugars, citrate or pectin and most laboratory synthesis methods deliver large precipitates, often containing vaterite or aragonite. To address this problem, we (i) adapted the method of carbonating a Ca(OH)2 slurry with CO2 gas to develop the first simple, cheap, safe and reproducible procedure using common laboratory equipment, to obtain calcite that reproducibly had a surface area of 14-17 m2/g and (ii) conducted a thorough characterization of the product. Scanning electron microscopy (SEM) revealed nanometer scale, rhombohedral crystals. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) confirmed highly crystalline, pure calcite that more closely resembles the dimensions of the biogenic calcite produced by algae in coccoliths than other methods for synthesizing calcite. We suggest that this calcite is useful when purity and high surface area are important.

  5. Calcium carbonate crystallization in the presence of taurine.

    PubMed

    Malkaj, P; Pierri, E; Dalas, E

    2006-05-01

    The kinetics of calcite (CaCO(3)) crystallization on calcite seed crystals in the presence of taurine was investigated by the constant composition method. The presence of taurine (4 x 10(- 5)- 4 x 10(-4)M) in the supersaturated solutions lead to calcite crystals with a characteristic discontinuous planes of growth and poor habit, as compared to the hombohedral morphology of the seed crystals. The acceleration effect of taurine on the crystal growth rate was 17-96%. The apparent order of the crystal growth was found to be 2.0+/- 0.2 typical for a surface diffusion-controlled spiral growth processes.

  6. Adjustment errors of sunstones in the first step of sky-polarimetric Viking navigation: studies with dichroic cordierite/ tourmaline and birefringent calcite crystals.

    PubMed

    Száz, Dénes; Farkas, Alexandra; Blahó, Miklós; Barta, András; Egri, Ádám; Kretzer, Balázs; Hegedüs, Tibor; Jäger, Zoltán; Horváth, Gábor

    2016-01-01

    According to an old but still unproven theory, Viking navigators analysed the skylight polarization with dichroic cordierite or tourmaline, or birefringent calcite sunstones in cloudy/foggy weather. Combining these sunstones with their sun-dial, they could determine the position of the occluded sun, from which the geographical northern direction could be guessed. In psychophysical laboratory experiments, we studied the accuracy of the first step of this sky-polarimetric Viking navigation. We measured the adjustment error e of rotatable cordierite, tourmaline and calcite crystals when the task was to determine the direction of polarization of white light as a function of the degree of linear polarization p. From the obtained error functions e(p), the thresholds p* above which the first step can still function (i.e. when the intensity change seen through the rotating analyser can be sensed) were derived. Cordierite is about twice as reliable as tourmaline. Calcite sunstones have smaller adjustment errors if the navigator looks for that orientation of the crystal where the intensity difference between the two spots seen in the crystal is maximal, rather than minimal. For higher p (greater than p crit) of incident light, the adjustment errors of calcite are larger than those of the dichroic cordierite (p crit=20%) and tourmaline (p crit=45%), while for lower p (less than p crit) calcite usually has lower adjustment errors than dichroic sunstones. We showed that real calcite crystals are not as ideal sunstones as it was believed earlier, because they usually contain scratches, impurities and crystal defects which increase considerably their adjustment errors. Thus, cordierite and tourmaline can also be at least as good sunstones as calcite. Using the psychophysical e(p) functions and the patterns of the degree of skylight polarization measured by full-sky imaging polarimetry, we computed how accurately the northern direction can be determined with the use of the Viking

  7. Chemical and physical evolution of dolomite precipitation at 180°C and 220°C from calcite and aragonite seeds

    NASA Astrophysics Data System (ADS)

    Kell-Duivestein, Isaac; Dietzel, Martin; Mavromatis, Vasileios

    2016-04-01

    In this present study an experimental approach is taken to gain a better understanding of secondary dolomite formation under diagenetic hydrothermal conditions. A series of 60 experiments were set up in closed bomb reactors with Teflon inserts to simulate exposure of calcium carbonate materials of (i) aragonite and (ii) calcite to hydrothermal conditions. 30 reactors were prepared using calcite as a seed material and 30 using aragonite. In each experiment 330mg of the seed calcium carbonate was placed in 30mL of 0.2M MgCl2 solution along with 252mg NaHCO3 to balance charges. 15 of each the calcite and aragonite prepared reactors were placed in an oven at 180°C and 15 of each at 220°C. Samples were then progressively removed from the ovens beginning in short time intervals and increasing the time apart as the phase transformations became less rapid (ie. after 3, 6, 13, 21, 31, 56 days *ongoing*). Samples were separated into fluid and solid phases by filtration for separate analysis. Fluids were analysed by titration for alkalinity and ICP-OES for elemental concentrations of major cations to determine the migration of major cations between the calcium carbonate seed material and the reaction fluid. Solid samples were analysed with FTIR-spectroscopy and X-ray diffraction of powdered smears on glass loading slides to identify the present mineral phases. Rietveld analysis was conducted on the XRD patterns to quantify the mineral phases and to determine the stoichiometry and the superstructure of the formed magnesite and dolomite. Although experiments are still running, several trends have been identified. Transformation of the aragonite seed material occurs at a much faster rate than transformation of the calcite seed material, with each precursor material first transforming into a Ca-rich magnesite. With increased reaction time the Ca-rich magnesite recrystallizes to purer phases of magnesite, the Ca concentration of the fluid increases as the Ca is liberated into

  8. Specific features of seeding and growth of bulk polar crystals

    NASA Astrophysics Data System (ADS)

    Tsvetkov, E. G.; Tyurikov, V. I.

    2000-07-01

    Formal analysis of seeding and growth of crystals exhibiting spontaneous polarization has been attempted using lithium iodate (α-LiIO 3) and barium metaborate (β-BaB 2O 4) as representative materials grown from aqueous and high-temperature solutions, respectively. We suggest that the specific growth features of nonlinear optical α-LiIO 3 and β-BaB 2O 4 crystals are being determined by formation and evolutionary restructuring of a double electric layer (DEL) at the growth interface. Both composition and structure of the DEL are governed by potential-determining ions of the growth medium as well as by the nature of crystal polarization and its properties. We have found that the composition and structure of the DEL together with the magnitude and direction of spontaneous polarization of the seed (crystal) predetermine the macrotwinning boundaries during seeding and subsequent stages of crystal growth as well as the formation of microtwin structures of various sizes. Similar reasoning is applied to possible crystal asymmetry, cellular growth, extinction of growth, etc. Model concepts of seeding and growth of bulk polar crystals are discussed.

  9. Puzzling calcite-III dimorphism: crystallography, high-pressure behavior, and pathway of single-crystal transitions

    NASA Astrophysics Data System (ADS)

    Pippinger, T.; Miletich, R.; Merlini, M.; Lotti, P.; Schouwink, P.; Yagi, T.; Crichton, W. A.; Hanfland, M.

    2015-01-01

    High-pressure phase transformations between the polymorphic forms I, II, III, and IIIb of CaCO3 were investigated by analytical in situ high-pressure high-temperature experiments on oriented single-crystal samples. All experiments at non-ambient conditions were carried out by means of Raman scattering, X-ray, and synchrotron diffraction techniques using diamond-anvil cells in the pressure range up to 6.5 GPa. The composite-gasket resistive heating technique was applied for all high-pressure investigations at temperatures up to 550 K. High-pressure Raman spectra reveal distinguishable characteristic spectral differences located in the wave number range of external modes with the occurrence of band splitting and shoulders due to subtle symmetry changes. Constraints from in situ observations suggest a stability field of CaCO3-IIIb at relatively low temperatures adjacent to the calcite-II field. Isothermal compression of calcite provides the sequence from I to II, IIIb, and finally, III, with all transformations showing volume discontinuities. Re-transformation at decreasing pressure from III oversteps the stability field of IIIb and demonstrates the pathway of pressure changes to determine the transition sequence. Clausius-Clapeyron slopes of the phase boundary lines were determined as: Δ P/Δ T = -2.79 ± 0.28 × 10-3 GPa K-1 (I-II); +1.87 ± 0.31 × 10-3 GPa K-1 (II/III); +4.01 ± 0.5 × 10-3 GPa K-1 (II/IIIb); -33.9 ± 0.4 × 10-3 GPa K-1 (IIIb/III). The triple point between phases II, IIIb, and III was determined by intersection and is located at 2.01(7) GPa/338(5) K. The pathway of transition from I over II to IIIb can be interpreted by displacement with small shear involved (by 2.9° on I/II and by 8.2° on II/IIIb). The former triad of calcite-I corresponds to the [20-1] direction in the P21/ c unit cell of phase II and to [101] in the pseudomonoclinic C setting of phase IIIb. Crystal structure investigations of triclinic CaCO3-III at non-ambient pressure

  10. Kinetic and thermodynamic factors controlling the distribution of SO 32- and Na + in calcites and selected aragonites

    NASA Astrophysics Data System (ADS)

    Busenberg, Eurybiades; Niel Plummer, L.

    1985-03-01

    Significant amounts of SO 42-, Na +, and OH - are incorporated in marine biogenic calcites. Biogenic high Mg-calcites average about 1 mole percent SO 42-. Aragonites and most biogenic low Mg-calcites contain significant amounts of Na +, but very low concentrations of SO 42-. The SO 42- content of non-biogenic calcites and aragonites investigated was below 100 ppm. The presence of Na + and SO 42- increases the unit cell size of calcites. The solid-solutions show a solubility minimum at about 0.5 mole percent SO 42- beyond which the solubility rapidly increases. The solubility product of calcites containing 3 mole percent SO 42- is the same as that of aragonite. Na + appears to have very little effect on the solubility product of calcites. The amounts of Na + and SO 42- incorporated in calcites vary as a function of the rate of crystal growth. The variation of the distribution coefficient ( D) of SO 42- in calcite at 25.0°C and 0.50 molal NaCl is described by the equation D = k 0 + k 1R where k 0 and k 1 are constants equal to 6.16 × 10 -6 and 3.941 × 10 -6, respectively, and R is the rate of crystal growth of calcite in mg·min -1·g -1 of seed. The data on Na + are consistent with the hypothesis that a significant amount of Na + occupies interstitial positions in the calcite structure. The distribution of Na + follows a Freundlich isotherm and not the Berthelot-Nernst distribution law. The numerical value of the Na + distribution coefficient in calcite is probably dependent on the number of defects in the calcite structure. The Na + contents of calcites are not very accurate indicators of environmental salinities.

  11. Kinetic and thermodynamic factors controlling the distribution of SO32- and Na+ in calcites and selected aragonites

    USGS Publications Warehouse

    Busenberg, E.; Niel, Plummer L.

    1985-01-01

    Significant amounts of SO42-, Na+, and OH- are incorporated in marine biogenic calcites. Biogenic high Mg-calcites average about 1 mole percent SO42-. Aragonites and most biogenic low Mg-calcites contain significant amounts of Na+, but very low concentrations of SO42-. The SO42- content of non-biogenic calcites and aragonites investigated was below 100 ppm. The presence of Na+ and SO42- increases the unit cell size of calcites. The solid-solutions show a solubility minimum at about 0.5 mole percent SO42- beyond which the solubility rapidly increases. The solubility product of calcites containing 3 mole percent SO42- is the same as that of aragonite. Na+ appears to have very little effect on the solubility product of calcites. The amounts of Na+ and SO42- incorporated in calcites vary as a function of the rate of crystal growth. The variation of the distribution coefficient (D) of SO42- in calcite at 25.0??C and 0.50 molal NaCl is described by the equation D = k0 + k1R where k0 and k1 are constants equal to 6.16 ?? 10-6 and 3.941 ?? 10-6, respectively, and R is the rate of crystal growth of calcite in mg??min-1??g-1 of seed. The data on Na+ are consistent with the hypothesis that a significant amount of Na+ occupies interstitial positions in the calcite structure. The distribution of Na+ follows a Freundlich isotherm and not the Berthelot-Nernst distribution law. The numerical value of the Na+ distribution coefficient in calcite is probably dependent on the number of defects in the calcite structure. The Na+ contents of calcites are not very accurate indicators of environmental salinities. ?? 1985.

  12. Calcite growth-rate inhibition by fulvic acids isolated from Big Soda Lake, Nevada, USA, The Suwannee River, Georgia, USA and by polycarboxylic acids

    USGS Publications Warehouse

    Reddy, Michael M.; Leenheer, Jerry

    2011-01-01

    Calcite crystallization rates are characterized using a constant solution composition at 25°C, pH=8.5, and calcite supersaturation (Ω) of 4.5 in the absence and presence of fulvic acids isolated from Big Soda Lake, Nevada (BSLFA), and a fulvic acid from the Suwannee River, Georgia (SRFA). Rates are also measured in the presence and absence of low-molar mass, aliphatic-alicyclic polycarboxylic acids (PCA). BSLFA inhibits calcite crystal-growth rates with increasing BSLFA concentration, suggesting that BSLFA adsorbs at growth sites on the calcite crystal surface. Calcite growth morphology in the presence of BSLFA differed from growth in its absence, supporting an adsorption mechanism of calcite-growth inhibition by BSLFA. Calcite growth-rate inhibition by BSLFA is consistent with a model indicating that polycarboxylic acid molecules present in BSLFA adsorb at growth sites on the calcite crystal surface. In contrast to published results for an unfractionated SRFA, there is dramatic calcite growth inhibition (at a concentration of 1 mg/L) by a SRFA fraction eluted by pH 5 solution from XAD-8 resin, indicating that calcite growth-rate inhibition is related to specific SRFA component fractions. A cyclic PCA, 1, 2, 3, 4, 5, 6-cyclohexane hexacarboxylic acid (CHXHCA) is a strong calcite growth-rate inhibitor at concentrations less than 0.1 mg/L. Two other cyclic PCAs, 1, 1 cyclopentanedicarboxylic acid (CPDCA) and 1, 1 cyclobutanedicarboxylic acid (CBDCA) with the carboxylic acid groups attached to the same ring carbon atom, have no effect on calcite growth rates up to concentrations of 10 mg/L. Organic matter ad-sorbed from the air onto the seed crystals has no effect on the measured calcite crystal-growth rates.

  13. Morphology Controls on Calcite Recrystallization.

    PubMed

    Heberling, Frank; Paulig, Leonie; Nie, Zhe; Schild, Dieter; Finck, Nicolas

    2016-11-01

    Environmental scientists and geoscientists working in different fields regard the reactivity of calcite and corresponding changes in its trace elemental- or isotopic composition from diametrically opposed points of view. As one extreme, calcite based environmental remediation strategies rely on the fast recrystallization of calcite and the concurrent uptake and immobilization of pollutants. Paleo-ecological investigations denote the other extreme, and rely on the invariability of calcite composition over geological periods of time. We use long-term radiotracer experiments to quantify recrystallization rates of seven types of calcite powder with diverse morphology and particle size distribution. On the one hand our results demonstrate the long-term metastability of calcite with equilibrated crystal surfaces even at isotopic dis-equilibrium. On the other hand, we document the extremely high reactivity and interfacial free energy of freshly ground, rough calcite. Our results indicate that bulk calcite recrystallization is an interfacial free energy driven Ostwald-ripening process, in which particle roughness effects dominate over the effect of crystal habitus and particle size. We confirm that the dynamic equilibrium exchange of crystal constituents between kink sites involves an activation barrier of about 25 kJ/mol. At room temperature the equilibrium exchange is limited to a near surface region and proceeds at a rate of (3.6 ± 1.4)·10(-13) mol/(m(2)·s).

  14. Crystallization of struvite from metastable region with different types of seed crystal

    NASA Astrophysics Data System (ADS)

    Ali, Imtiaj; Schneider, Phil Andrew

    2005-05-01

    The main feature of this paper was to recognize struvite crystallization in the metastable region of supersaturation. Thermodynamic equilibria of struvite were simulated to identify the minimum struvite solubility limit, thereafter validated by existing thermodynamic modelling packages such as PHREEQC and the derived data from existing struvite solubility curve. Using laser light scattering detection, spontaneous nucleation was identified by the slow increase of pH in a supersaturated solution of struvite. The crystallization experiment, conducted close to the saturation region in metastable zone, initiated struvite growth. The conducted experiment showed that mother crystal (struvite) was more effective as seeds for struvite crystallization.

  15. Crystallization of pumpkin seed globulin: growth and dissolution kinetics

    NASA Astrophysics Data System (ADS)

    Malkin, Alexander J.; McPherson, Alexander

    1993-10-01

    Quasi-elastic light scattering was used to investigate the nucleation and crystallization of pumpkin ( Cucurbita) seed globulin. The diameter of the pumpkin globulin monomer was measured to be ≈ 5-6 nm. The supersaturation dependence of critical nucleus size was obtained, and this allowed an estimate of the interfacial free energy to be α ≈ 6.1 x 10 -2 erg/cm 2. The crystallization and dissolution kinetics were investigated for 4.9-16 mg/ml protein solutions containing 1-7% NaCl. The solubility data as a function of precipitant concentration and temperature were obtained and these will be utilized for optimization of the crystallization conditions for the pumpkin globulin.

  16. Stereo-epitaxial growth of single-crystal Ni nanowires and nanoplates from aligned seed crystals

    NASA Astrophysics Data System (ADS)

    Lee, Hyoban; Yoo, Youngdong; Kang, Taejoon; Lee, Jiyoung; Kim, Eungwang; Fang, Xiaosheng; Lee, Sungyul; Kim, Bongsoo

    2016-05-01

    Epitaxially grown anisotropic Ni nanostructures are promising building blocks for the development of miniaturized and stereo-integrated data storage kits because they can store multiple magnetic domain walls (DWs). Here, we report stereo-epitaxially grown single-crystalline Ni nanowires (NWs) and nanoplates, and their magnetic properties. Vertical and inclined Ni NWs were grown at the center and edge regions of c-cut sapphire substrates, respectively. Vertical Ni nanoplates were grown on r-cut sapphire substrates. The morphology and growth direction of Ni nanostructures can be steered by seed crystals. Cubic Ni seeds grow into vertical Ni NWs, tetrahedral Ni seeds grow into inclined Ni NWs, and triangular Ni seeds grow into vertical Ni nanoplates. The shapes of the Ni seeds are determined by the interfacial energy between the bottom plane of the seeds and the substrates. The as-synthesized Ni NWs and nanoplates have blocking temperature values greater than 300 K at 500 Oe, verifying that these Ni nanostructures can form large magnetic DWs with high magnetic anisotropy properties. We anticipate that epitaxially grown Ni NWs and nanoplates will be used in various types of 3-dimensional magnetic devices.Epitaxially grown anisotropic Ni nanostructures are promising building blocks for the development of miniaturized and stereo-integrated data storage kits because they can store multiple magnetic domain walls (DWs). Here, we report stereo-epitaxially grown single-crystalline Ni nanowires (NWs) and nanoplates, and their magnetic properties. Vertical and inclined Ni NWs were grown at the center and edge regions of c-cut sapphire substrates, respectively. Vertical Ni nanoplates were grown on r-cut sapphire substrates. The morphology and growth direction of Ni nanostructures can be steered by seed crystals. Cubic Ni seeds grow into vertical Ni NWs, tetrahedral Ni seeds grow into inclined Ni NWs, and triangular Ni seeds grow into vertical Ni nanoplates. The shapes of the Ni

  17. Composite Magnetite and Protein Containing CaCO3 Crystals. External Manipulation and Vaterite → Calcite Recrystallization-Mediated Release Performance.

    PubMed

    Sergeeva, Alena; Sergeev, Roman; Lengert, Ekaterina; Zakharevich, Andrey; Parakhonskiy, Bogdan; Gorin, Dmitry; Sergeev, Sergey; Volodkin, Dmitry

    2015-09-30

    Biocompatibility and high loading capacity of mesoporous CaCO3 vaterite crystals give an option to utilize the polycrystals for a wide range of (bio)applications. Formation and transformations of calcium carbonate polymorphs have been studied for decades, aimed at both basic and applied research interests. Here, composite multilayer-coated calcium carbonate polycrystals containing Fe3O4 magnetite nanoparticles and model protein lysozyme are fabricated. The structure of the composite polycrystals and vaterite → calcite recrystallization kinetics are studied. The recrystallization results in release of both loaded protein and Fe3O4 nanoparticles (magnetic manipulation is thus lost). Fe3O4 nanoparticles enhance the recrystallization that can be induced by reduction of the local pH with citric acid and reduction of the polycrystal crystallinity. Oppositely, the layer-by-layer assembled poly(allylamine hydrochloride)/poly(sodium styrenesulfonate) polyelectrolyte coating significantly inhibits the vaterite → calcite recrystallization (from hours to days) most likely due to suppression of the ion exchange giving an option to easily tune the release kinetics for a wide time scale, for example, for prolonged release. Moreover, the recrystallization of the coated crystals results in formulation of multilayer capsules keeping the feature of external manipulation. This study can help to design multifunctional microstructures with tailor-made characteristics for loading and controlled release as well as for external manipulation.

  18. A comparative study of seed crystals for the phosphorus crystallization process.

    PubMed

    Yim, S; Kim, E-H

    2004-07-01

    This study was performed to select a preferred seed crystal material for the phosphorus crystallization process through a comparative study of four materials: electron arc furnace, blast furnace and converter slag, and phosphate rock. Leaching and phosphorus removal tests were conducted to evaluate the efficacy of the four materials as seeding agents. Converter slag demonstrated a much larger leaching capacity with respect to calcium and hydroxide ions than did either electron arc furnace or blast furnace slag. The average phosphorus removal efficiencies of phosphorus rock, and the electron arc furnace, blast furnace and converter slag were 35.9%, 74.2%, 99.1%, and 94.5% following 20, 17, 32, and 175 days of leach time, respectively. Consideration of both technical and cost factors suggests that converter slag may have competitive advantages over the other three seed materials. X-ray diffraction (XRD) analysis showed that peak patterns for hydroxyapatite increased slightly as the hydrous flow time was extended. Scanning electron micrograph (SEM) images revealed that finely distributed cubic crystals were deposited on the surfaces of converter slag. When analyzed by energy dispersive x-ray spectrometer (EDS) mapping, the crystals gave a composition mole ratio (Ca/P) of 1.97 and they were determined to be hydroxyapatite.

  19. Stereo-epitaxial growth of single-crystal Ni nanowires and nanoplates from aligned seed crystals.

    PubMed

    Lee, Hyoban; Yoo, Youngdong; Kang, Taejoon; Lee, Jiyoung; Kim, Eungwang; Fang, Xiaosheng; Lee, Sungyul; Kim, Bongsoo

    2016-05-21

    Epitaxially grown anisotropic Ni nanostructures are promising building blocks for the development of miniaturized and stereo-integrated data storage kits because they can store multiple magnetic domain walls (DWs). Here, we report stereo-epitaxially grown single-crystalline Ni nanowires (NWs) and nanoplates, and their magnetic properties. Vertical and inclined Ni NWs were grown at the center and edge regions of c-cut sapphire substrates, respectively. Vertical Ni nanoplates were grown on r-cut sapphire substrates. The morphology and growth direction of Ni nanostructures can be steered by seed crystals. Cubic Ni seeds grow into vertical Ni NWs, tetrahedral Ni seeds grow into inclined Ni NWs, and triangular Ni seeds grow into vertical Ni nanoplates. The shapes of the Ni seeds are determined by the interfacial energy between the bottom plane of the seeds and the substrates. The as-synthesized Ni NWs and nanoplates have blocking temperature values greater than 300 K at 500 Oe, verifying that these Ni nanostructures can form large magnetic DWs with high magnetic anisotropy properties. We anticipate that epitaxially grown Ni NWs and nanoplates will be used in various types of 3-dimensional magnetic devices.

  20. Elastic constants of calcite

    USGS Publications Warehouse

    Peselnick, L.; Robie, R.A.

    1962-01-01

    The recent measurements of the elastic constants of calcite by Reddy and Subrahmanyam (1960) disagree with the values obtained independently by Voigt (1910) and Bhimasenachar (1945). The present authors, using an ultrasonic pulse technique at 3 Mc and 25??C, determined the elastic constants of calcite using the exact equations governing the wave velocities in the single crystal. The results are C11=13.7, C33=8.11, C44=3.50, C12=4.82, C13=5.68, and C14=-2.00, in units of 1011 dyncm2. Independent checks of several of the elastic constants were made employing other directions and polarizations of the wave velocities. With the exception of C13, these values substantially agree with the data of Voigt and Bhimasenachar. ?? 1962 The American Institute of Physics.

  1. The grinding tip of the sea urchin tooth exhibits exquisite control over calcite crystal orientation and Mg distribution.

    PubMed

    Ma, Yurong; Aichmayer, Barbara; Paris, Oskar; Fratzl, Peter; Meibom, Anders; Metzler, Rebecca A; Politi, Yael; Addadi, Lia; Gilbert, P U P A; Weiner, Steve

    2009-04-14

    The sea urchin tooth is a remarkable grinding tool. Even though the tooth is composed almost entirely of calcite, it is used to grind holes into a rocky substrate itself often composed of calcite. Here, we use 3 complementary high-resolution tools to probe aspects of the structure of the grinding tip: X-ray photoelectron emission spectromicroscopy (X-PEEM), X-ray microdiffraction, and NanoSIMS. We confirm that the needles and plates are aligned and show here that even the high Mg polycrystalline matrix constituents are aligned with the other 2 structural elements when imaged at 20-nm resolution. Furthermore, we show that the entire tooth is composed of 2 cooriented polycrystalline blocks that differ in their orientations by only a few degrees. A unique feature of the grinding tip is that the structural elements from each coaligned block interdigitate. This interdigitation may influence the fracture process by creating a corrugated grinding surface. We also show that the overall Mg content of the tooth structural elements increases toward the grinding tip. This probably contributes to the increasing hardness of the tooth from the periphery to the tip. Clearly the formation of the tooth, and the tooth tip in particular, is amazingly well controlled. The improved understanding of these structural features could lead to the design of better mechanical grinding and cutting tools.

  2. The grinding tip of the sea urchin tooth exhibits exquisite control over calcite crystal orientation and Mg distribution

    PubMed Central

    Ma, Yurong; Aichmayer, Barbara; Paris, Oskar; Fratzl, Peter; Meibom, Anders; Metzler, Rebecca A.; Politi, Yael; Addadi, Lia; Gilbert, P. U. P. A.; Weiner, Steve

    2009-01-01

    The sea urchin tooth is a remarkable grinding tool. Even though the tooth is composed almost entirely of calcite, it is used to grind holes into a rocky substrate itself often composed of calcite. Here, we use 3 complementary high-resolution tools to probe aspects of the structure of the grinding tip: X-ray photoelectron emission spectromicroscopy (X-PEEM), X-ray microdiffraction, and NanoSIMS. We confirm that the needles and plates are aligned and show here that even the high Mg polycrystalline matrix constituents are aligned with the other 2 structural elements when imaged at 20-nm resolution. Furthermore, we show that the entire tooth is composed of 2 cooriented polycrystalline blocks that differ in their orientations by only a few degrees. A unique feature of the grinding tip is that the structural elements from each coaligned block interdigitate. This interdigitation may influence the fracture process by creating a corrugated grinding surface. We also show that the overall Mg content of the tooth structural elements increases toward the grinding tip. This probably contributes to the increasing hardness of the tooth from the periphery to the tip. Clearly the formation of the tooth, and the tooth tip in particular, is amazingly well controlled. The improved understanding of these structural features could lead to the design of better mechanical grinding and cutting tools. PMID:19332795

  3. Molecular dynamics simulations of polymer crystallization via self-seeding

    NASA Astrophysics Data System (ADS)

    Luo, Chuanfu; Sommer, Jens-Uwe

    2010-03-01

    We use large scale molecular dynamics (MD) to simulate the processes of polymer crystallization with a coarse-grained model. In total we are able to simulate 1000 polymer chains made of 1000 monomers each, a system large enough to compare to experimental relevant, entangled melts. It is found that some micro crystalline domains (MCDs) can survive slightly above the apparent melting temperature after a consistent cooling and reheating cycle. We chose the stablest MCD as a baby seed and let it grow at a constant quenched temperature. A single lamella can be formed via this self-seeding process. We observe the growth pathway and analyze the chain dynamics especially at the growth front.[4pt] [1] C. Luo and J. Sommer, Comp Phys. Comm. 180, 1382 (2009)[0pt] [2] C. Luo and J. Sommer, Phys. Rev. Lett. 102, 147801 (2009)[0pt] [3] J-J. Xu, Y. Ma, W.B. Hu, M. Rehahn and G. Reiter, Nature Materials 8, 348 (2009)

  4. Large single domain 123 material produced by seeding with single crystal rare earth barium copper oxide single crystals

    DOEpatents

    Todt, Volker; Miller, Dean J.; Shi, Donglu; Sengupta, Suvankar

    1998-01-01

    A method of fabricating bulk YBa.sub.2 Cu.sub.3 O.sub.x where compressed powder oxides and/or carbonates of Y and Ba and Cu present in mole ratios to form YBa.sub.2 Cu.sub.3 O.sub.x are heated in the presence of a Nd.sub.1+x Ba.sub.2-x Cu.sub.3 O.sub.y seed crystal to a temperature sufficient to form a liquid phase in the YBa.sub.2 Cu.sub.3 O.sub.x while maintaining the seed crystal solid. The materials are slowly cooled to provide a YBa.sub.2 Cu.sub.3 O.sub.x material having a predetermined number of domains between 1 and 5. Crack-free single domain materials can be formed using either plate shaped seed crystals or cube shaped seed crystals with a pedestal of preferential orientation material.

  5. Growth of Cadmium-Zinc Telluride Crystals by Controlled Seeding Contactless Physical Vapor Transport

    NASA Technical Reports Server (NTRS)

    Palosz, W.; Grasza, K.; Gillies, D.; Jerman, G.

    1996-01-01

    Bulk crystals of cadmium-zinc telluride, 23 mm in diameter and up to 45 grams in weight were grown. Controlled seed formation procedure was used to limit the number of grains in the crystal. Most uniform distribution of ZnTe in the crystals was obtained using excess (Cd + Zn) pressure in the ampoule.

  6. Segregation during directional melting and its implications on seeded crystal growth: A theoretical analysis

    NASA Technical Reports Server (NTRS)

    Bourret, E. D.; Favier, J. J.; Witt, A. F.

    1982-01-01

    Directional melting of binary systems, as encountered during seeding in melt growth, is analyzed for concurrent compositional changes at the crystal-melt interface. It is shown that steady state conditions cannot normally be reached during seeding and that the growth interface temperature at the initial stages of seeded growth is a function of backmelt conditions. The theoretical treatment is numerically applied to Hg1-xCdXTe and Ga-doped Ge.

  7. Fracture-aperture alteration induced by calcite precipitation

    NASA Astrophysics Data System (ADS)

    Jones, T.; Detwiler, R. L.

    2013-12-01

    Mineral precipitation significantly alters the transport properties of fractured rock. Chemical solubility gradients that favor precipitation induce mineral growth, which decreases the local aperture and alters preferential flow paths. Understanding the resulting development of spatial heterogeneities is necessary to predict the evolution of transport properties in the subsurface. We present experimental results that quantify the relationship between mineral precipitation and aperture alteration in a transparent analog fracture, 7.62cm x 7.62cm, with a uniform aperture of ~200 μm. Prior to flow experiments, a pump circulated a super-saturated calcite solution over the bottom glass, coating the glass surface with calcite. This method of seeding resulted in clusters of calcite crystals with large reactive surface area and provided micro-scale variability in the aperture field. A continuous flow syringe pump injected a reactive fluid into the fracture at 0.5 ml/min. The fluid was a mixture of sodium bicarbonate (NaHCO3, 0.02M) and calcium chloride (CaCl2 0.0004M) with a saturation index, Ω, of 8.51 with respect to calcite. A strobed LED panel backlit the fracture and a high-resolution CCD camera monitored changes in transmitted light intensity. Light transmission techniques provided a quantitative measurement of fracture aperture over the flow field. Results from these preliminary experiments showed growth near the inlet of the fracture, with decreasing precipitation rates in the flow direction. Over a period of two weeks, the fracture aperture decreased by 17% within the first 4mm of the inlet. Newly precipitated calcite bridged individual crystal clusters and smoothed the reacting surface. This observation is an interesting contradiction to the expectation of surface roughening induced by mineral growth. Additionally, the aperture decreased uniformly across the width of the fracture due to the initial aperture distribution. Future experiments of precipitation

  8. The Influence of Kinetic Growth Factors on the Clumped Isotope Composition of Calcite

    NASA Astrophysics Data System (ADS)

    Hunt, J. D.; Watkins, J. M.; Tripati, A.; Ryerson, F. J.; DePaolo, D. J.

    2014-12-01

    Clumped isotope paleothermometry is based on the association of 13C and 18O within carbonate minerals. Although the influence of temperature on equilibrium 13C-18O bond ordering has been studied, recent oxygen isotope studies of inorganic calcite demonstrate that calcite grown in laboratory experiments and in many natural settings does not form in equilibrium with water. It is therefore likely that the carbon and clumped isotope composition of these calcite crystals are not representative of true thermodynamic equilibrium. To isolate kinetic clumped isotope effects that arise at the mineral-solution interface, clumped isotopic equilibrium of DIC species must be maintained. This can be accomplished by dissolving the enzyme carbonic anhydrase (CA) into the solution, thereby reducing the time required for isotopic equilibration of DIC species by approximately two orders of magnitude between pH 7.7 and 9.3. We conduct calcite growth experiments aimed specifically at measuring the pH-dependence of kinetic clumped isotope effects during non-equilibrium precipitation of calcite. We precipitated calcite from aqueous solution at a constant pH and controlled supersaturation over the pH range 7.7-9.3 in the presence of CA. For each experiment, a gas mixture of N2 and CO2 is bubbled through a beaker of solution without seed crystals. As CO2 from the gas dissolves into solution, calcite crystals grow on the beaker walls. The pH of the solution is maintained by use of an autotitrator with NaOH as the titrant. We control the temperature, pH, the pCO2 of the gas inflow, and the gas inflow rate, and monitor the total alkalinity, the pCO2 of the gas outflow, and the amount of NaOH added. A constant crystal growth rate of ~1.6 mmol/m2/hr is maintained over all experiments. Results from these experiments are compared to predictions from a recently-developed isotopic ion-by-ion growth model of calcite. The model describes the rate, temperature and pH dependence of oxygen isotope uptake

  9. Crystalline order of a water/glycine film coadsorbed on the (104) calcite surface.

    PubMed

    Magdans, Uta; Torrelles, Xavier; Angermund, Klaus; Gies, Hermann; Rius, Jordi

    2007-04-24

    For biomineralization processes, the interaction of the surface of calcite crystals with organic molecules is of particular importance. Especially, biologically controlled biomineralization as in exoskeletons of mollusks and echinoderms, e.g., sea urchin with single-crystal-like spines and shells,1-3 requires molecular control of seed formation and growth process. So far, experiments showing the obvious influence of organic molecules on the morphology and habit of calcite crystals have demonstrated the molecular dimension of the interaction.4-7 Details of the kinetics of growth and dissolution of mineral surfaces influenced by additives are available,8,9 but other experimental data about the structure of the organic/inorganic interface on the atomic scale are rare. On the other hand, complicated organic macromolecules which are involved in biomineralization are numerous, with only a small fraction solved in structure and function so far.10-13 Therefore, model systems have to be designed to provide a basic understanding for the interaction process.14 Using grazing incidence X-ray diffraction combined with molecular modeling techniques, we show that glycine molecules order periodically on the calcite (104) face in competition with the solvent water when exposed to an aqueous solution of the most simple amino acid. In contrast to the general concept of the charge-matching fit of organic molecules on mineral surfaces,4,14 glycine is not attached to the calcite surface directly but substitutes for water molecules in the second hydration layer.

  10. Truncated tetrahedron seed crystals initiating stereoaligned growth of FeSi nanowires.

    PubMed

    Kim, Si-in; Yoon, Hana; Seo, Kwanyong; Yoo, Youngdong; Lee, Sungyul; Kim, Bongsoo

    2012-10-23

    We have synthesized epitaxially grown freestanding FeSi nanowires (NWs) on an m-Al(2)O(3) substrate by using a catalyst-free chemical vapor transport method. FeSi NW growth is initiated from FeSi nanocrystals, formed on a substrate in a characteristic shape with a specific orientation. Cross-section TEM analysis of seed crystals reveals the crystallographic structure and hidden geometry of the seeds. Close correlation of geometrical shapes and orientations of the observed nanocrystals with those of as-grown NWs indicates that directional growth of NWs is initiated from the epitaxially formed seed crystals. The diameter of NWs can be controlled by adjusting the composition of Si in a Si/C mixture. The epitaxial growth method for FeSi NWs via seed crystals could be employed to heteroepitaxial growth of other compound NWs.

  11. Influence of calcium oxalate crystal accumulation on the calcium content of seeds from Medicago truncatula

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Crystals of calcium oxalate often form in cells adjacent to the vascular bundles in the tissues along the xylem stream. This spatial crystal pattern suggests a role for calcium oxalate formation in regulating calcium transport and partitioning to edible organs such as seeds. To investigate this pote...

  12. Seeding for sirtuins: microseed matrix seeding to obtain crystals of human Sirt3 and Sirt2 suitable for soaking

    SciTech Connect

    Rumpf, Tobias; Gerhardt, Stefan; Einsle, Oliver; Jung, Manfred

    2015-11-18

    In the present study, microseed matrix seeding was successfully applied to obtain a large number of crystals of the human sirtuin isotypes Sirt2 and Sirt3. These crystals appeared predictably in diverse crystallization conditions, diffracted to a higher resolution than reported in the literature and were subsequently used to study the protein–ligand interactions of two indole inhibitors. Sirtuins constitute a family of NAD{sup +}-dependent enzymes that catalyse the cleavage of various acyl groups from the ∊-amino group of lysines. They regulate a series of cellular processes and their misregulation has been implicated in various diseases, making sirtuins attractive drug targets. To date, only a few sirtuin modulators have been reported that are suitable for cellular research and their development has been hampered by a lack of structural information. In this work, microseed matrix seeding (MMS) was used to obtain crystals of human Sirt3 in its apo form and of human Sirt2 in complex with ADP ribose (ADPR). Crystal formation using MMS was predictable, less error-prone and yielded a higher number of crystals per drop than using conventional crystallization screening methods. The crystals were used to solve the crystal structures of apo Sirt3 and of Sirt2 in complex with ADPR at an improved resolution, as well as the crystal structures of Sirt2 in complex with ADPR and the indoles EX527 and CHIC35. These Sirt2–ADPR–indole complexes unexpectedly contain two indole molecules and provide novel insights into selective Sirt2 inhibition. The MMS approach for Sirt2 and Sirt3 may be used as the basis for structure-based optimization of Sirt2/3 inhibitors in the future.

  13. Growth of lead magnesium niobate-lead titanate single crystals by seeded polycrystal conversion

    NASA Astrophysics Data System (ADS)

    Scotch, Adam Matthew

    Relaxor-based ferroelectric single crystals of Pb(Mg1/3Nb 2/3)O3-PbTiO3 [PMN-PT] have been produced via the Seeded Polycrystal Conversion [SPC] technique. Polycrystalline precursors of PMN-PT are converted to single crystals by inducing the boundary of a seed crystal to migrate through a polycrystalline matrix. The quality of PMN-PT single crystals grown by SPC is directly influenced by the microstructure of the polycrystalline precursor. The goal of this work was to examine the factors that controlled the final microstructure of the matrix and grown single crystals and to characterize their effects on properties. Sintering in oxygen was necessary to obtain fully dense matrix microstructures, which, in turn, produced pore-free single crystals. The primary role of oxygen was to remove insoluble gases before densification began, then to reduce the internal pressure by diffusing out and allowing the pores to close from pressures derived from their own curvatures. The presence of a PbO liquid phase assisted this process by enhancing the densification rate in the early stages of sintering. In contrast, fully-dense, hot-pressed samples of PMN-35PT with excess PbO underwent a de-densification process during the annealing treatments which was attributed to pore formation from internally evolved gases. Transparent single crystals with maximum strain values of 0.72% at 46 kV/cm, d33 ˜2180 pC/N, and a room temperature dielectric constant of ˜5300 were obtained for poled <001> oriented crystals of PMN-30mol.%PT. The dielectric behavior of {001} oriented single crystals was found to be highly dependent on the initial orientation of the seed crystal. For example, {111} seeded crystals grown in oxygen yielded Kmax values of ˜33000, while {001} seeded crystals grown in oxygen had Kmax values of ˜25000. In addition, the Tmax values were 3 to 5°C higher for crystals grown from {001} seeds, compared to {111} seeds.

  14. Influence of calcium oxalate crystal accumulation on the calcium content of seeds from Medicago truncatula.

    PubMed

    Nakata, Paul A

    2012-04-01

    Crystals of calcium oxalate often form in cells adjacent to the vascular bundles in the tissues along the xylem stream. This spatial crystal pattern suggests a role for calcium oxalate formation in regulating calcium transport and partitioning to edible organs such as seeds. To investigate this potential role, microscopic and biochemical comparisons were conducted on the different tissues of Medicago truncatula wild-type and the calcium oxalate defective (cod) 5 which lacks the ability to accumulate prismatic crystals in the cells adjacent to the vascular bundles. Calcium measurements showed that cod5 seeds had more calcium and cod5 pods contained less calcium than the corresponding wild-type tissues. Roots, stems, and leaves from cod5 and wild-type had similar calcium content. Although cod5 was devoid of prismatic crystals, cod5 pods were observed to form druse crystals of calcium oxalate not found in wild-type pods. Taken together these findings suggest a functional role for calcium oxalate formation in regulating calcium transport to the seeds. Regulating calcium uptake at the roots also appeared to be another point of control in determining seed calcium content. Overall, regulating the long distance transport and partitioning of calcium to the seeds appears to be a complex process with multiple points of control.

  15. Large single domain 123 material produced by seeding with single crystal rare earth barium copper oxide single crystals

    DOEpatents

    Todt, V.; Miller, D.J.; Shi, D.; Sengupta, S.

    1998-07-07

    A method of fabricating bulk YBa{sub 2}Cu{sub 3}O{sub x} where compressed powder oxides and/or carbonates of Y and Ba and Cu present in mole ratios to form YBa{sub 2}Cu{sub 3}O{sub x} are heated in the presence of a Nd{sub 1+x}Ba{sub 2{minus}x}Cu{sub 3}O{sub y} seed crystal to a temperature sufficient to form a liquid phase in the YBa{sub 2}Cu{sub 3}O{sub x} while maintaining the seed crystal solid. The materials are slowly cooled to provide a YBa{sub 2}Cu{sub 3}O{sub x} material having a predetermined number of domains between 1 and 5. Crack-free single domain materials can be formed using either plate shaped seed crystals or cube shaped seed crystals with a pedestal of preferential orientation material. 7 figs.

  16. Purification, crystallization and initial crystallographic characterization of the Ginkgo biloba 11S seed globulin ginnacin

    SciTech Connect

    Jin, Tengchuan; Chen, Yu-Wei; Howard, Andrew; Zhang, Yu-Zhu

    2008-07-01

    The crystallization of ginnacin, the 11S seed storage protein from G. biloba, is reported. Ginkgo biloba, a well known ‘living fossil’ native to China, is grown worldwide as an ornamental shade plant. Medicinal and nutritional uses of G. biloba in Asia have a long history. However, ginkgo seed proteins have not been well studied at the biochemical and molecular level. In this study, the G. biloba 11S seed storage protein ginnacin was purified by sequential anion-exchange and gel-filtration chromatography. A crystallization screen was performed and well diffracting single crystals were obtained by the vapor-diffusion method. A molecular-replacement structural solution has been obtained. There are six protomers in an asymmetric unit. Structure refinement is currently in progress.

  17. In-situ growth of calcite at Devils Hole, Nevada--Comparison of field and laboratory rates to a 500,000 year record of near-equilibrium calcite growth

    USGS Publications Warehouse

    Plummer, L. Niel; Busenberg, Eurybiades; Riggs, Alan C.

    2000-01-01

    Calcite grew continuously for 500,000 years on the submerged walls of an open fault plane (Devils Hole) in southern Nevada, U.S.A. at rates of 0.3 to 1.3 mm/ka, but ceased growing approximately 60,000 years ago, even though the fault plane remained open and was continuously submerged. The maximum initial in-situ growth rate on pre-weighed crystals of Iceland spar placed in Devils Hole (calcite saturation index, SI, is 0.16 to 0.21 at 33.7 °C) for growth periods of 0.75 to 4.5 years was 0.22 mm/ka. Calcite growth on seed crystals slowed or ceased following initial contact with Devils Hole groundwater. Growth rates measured in synthetic Ca-HCO3 solutions at 34 °C, CO2 partial pressures of 0.101, 0.0156 (similar to Devils Hole groundwater) and 0.00102 atm, and SI values of 0.2 to 1.9 were nearly independent of PCO2, decreased with decreasing saturation state, and extrapolated through the historical Devils Hole rate. The results show that calcite growth rate is highly sensitive to saturation state near equilibrium. A calcite crystal retrieved from Devils Hole, and used without further treatment of its surface, grew in synthetic Devils Hole groundwater when the saturation index was raised nearly 10-fold that of Devils Hole water, but the rate was only 1/4 that of fresh laboratory crystals that had not contacted Devils Hole water. Apparently, inhibiting processes that halted calcite growth in Devils Hole 60,000 years ago continue today.

  18. In-situ growth of calcite at Devils Hole, Nevada: Comparison of field and laboratory rates to a 500,000 year record of near-equilibrium calcite growth

    USGS Publications Warehouse

    Plummer, L.N.; Busenberg, E.; Riggs, A.C.

    2000-01-01

    Calcite grew continuously for 500,000 years on the submerged walls of an open fault plane (Devils Hole) in southern Nevada, U.S.A. at rates of 0.3 to 1.3 mm/ka, but ceased growing approximately 60,000 years ago, even though the fault plane remained open and was continuously submerged. The maximum initial in-situ growth rate on pre-weighed crystals of Iceland spar placed in Devils Hole (calcite saturation index, SI, is 0.16 to 0.21 at 33.7??C) for growth periods of 0.75 to 4.5 years was 0.22 mm/ka. Calcite growth on seed crystals slowed or ceased following initial contact with Devils Hole groundwater. Growth rates measured in synthetic Ca-HCO3 solutions at 34??C, CO2 partial pressures of 0.101, 0.0156 (similar to Devils Hole groundwater) and 0.00102 atm, and SI values of 0.2 to 1.9 were nearly independent of P(CO)(2), decreased with decreasing saturation state, and extrapolated through the historical Devils Hole rate. The results show that calcite growth rate is highly sensitive to saturation state near equilibrium. A calcite crystal retrieved from Devils Hole, and used without further treatment of its surface, grew in synthetic Devils Hole groundwater when the saturation index was raised nearly 10-fold that of Devils Hole water, but the rate was only 1/4 that of fresh laboratory crystals that had not contacted Devils Hole water. Apparently, inhibiting processes that halted calcite growth in Devils Hole 60,000 years ago continue today.

  19. Fabrication of interconnected porous calcite by bridging calcite granules with dicalcium phosphate dihydrate and their histological evaluation.

    PubMed

    Ishikawa, Kunio; Koga, Noriko; Tsuru, Kanji; Takahashi, Ichiro

    2015-10-28

    Interconnected porous calcite has attracted attention as an artificial bone replacement material and as a precursor for the fabrication of carbonate apatite, which is also an artificial bone replacement material. In this study, calcite granules were exposed to acidic calcium phosphate solution, and the feasibility of fabricating interconnected porous calcite using this process was evaluated. No setting reaction was observed under the non-loading condition. In contrast, under loading conditions, calcite granules were bridged with dicalcium phosphate dihydrate crystals, and the calcite granules set into interconnected porous calcite foam. When applied 0.4 MPa of loading pressure during sample preparation, compressive strength of the obtained interconnected porous calcite was approximately 1.5 MPa. The exposure of the calcite granules to acidic calcium phosphate solution under loading conditions was the key for the setting reaction to occur. This is because calcite granules cannot contact one another under the non-loading condition because of bubble formation on the surfaces of the calcite granules. The interconnected porous calcite revealed excellent tissue response, and new bone was able to penetrate into the porous calcite two weeks after implantation. This article is protected by copyright. All rights reserved.

  20. Using natural seeding material to generate nucleation in protein crystallization experiments.

    PubMed

    D'Arcy, Allan; Mac Sweeney, Aengus; Haber, Alexander

    2003-07-01

    The nucleation event in protein crystallization is a part of the process that is poorly controlled. It is generally accepted that the protein should be in the metastable phase for crystal growth, but for nucleation higher levels of saturation are needed. Formation of nuclei in bulk solvent requires interaction of protein molecules until a critical size of aggregate is created. In many crystallization experiments sufficiently high levels of saturation are not reached to allow this critical nucleation event to occur. If an environment can be created that favours a higher local concentration of macromolecules, the energy barrier for nucleation may be lowered. When seeds are introduced at lower levels of saturation in a crystallization experiment, nucleation may be facilitated and crystal growth initiated. In this study, the use of natural materials as stable seeds for nucleation has been investigated. The method makes it possible to introduce seeds into crystallization trials at any stage of the experiment using both microbatch and vapour-diffusion methods.

  1. Dislocation formation in seed crystals induced by feedstock indentation during growth of quasimono crystalline silicon ingots

    NASA Astrophysics Data System (ADS)

    Trempa, M.; Beier, M.; Reimann, C.; Roßhirth, K.; Friedrich, J.; Löbel, C.; Sylla, L.; Richter, T.

    2016-11-01

    In this work the dislocation formation in the seed crystal induced by feedstock indentation during the growth of quasimono (QM) silicon ingots for photovoltaic application was investigated. It could be shown by special laboratory indentation experiments that the formed dislocations propagate up to several millimeters deep into the volume of the seed crystal in dependence on the applied pressure of the feedstock particles on the surface of the seed crystal. Further, it was demonstrated that these dislocations if they were not back-melted during the seeding process grow further into the silicon ingot and drastically reduce its material quality. An estimation of the apparent pressure values in a G5 industrial crucible/feedstock setup reveals that the indentation phenomenon is a critical issue for the industrial production of QM silicon ingots. Therefore, some approaches to avoid/reduce the indentation events were tested with the result, that the most promising solution should be the usage of suitable feedstock particles as coverage of the seed.

  2. Alternate deposition of oriented calcite and amino acid layer on calcite substrates.

    PubMed

    Qiao, Li; Feng, Qingling; Li, Zhuo; Lu, Shanshan

    2008-10-30

    Material synthesis inspired by novel nacre architecture and mechanism is popular and has attracted more and more attention. In this paper, iso-oriented calcite tablets/layers and amino acid layers were formed alternately on calcite wafers. It is interesting that the neonatal calcite tablets/layers have the same crystal orientation with their inorganic substrates through amino acid layers. It is quite possible that the amino acid layers in this study could transfer crystal orientation from formed inorganic layers to neighboring neonatal layers due to their fixed and appropriate structures, which may imply the process of nacre formation, and the role of aligned organic matrix sheets in nacre. Moreover, it could provide a new way to produce oriented calcite tablets/layers.

  3. Modeling the evolution of complex conductivity during calcite precipitation on glass beads

    NASA Astrophysics Data System (ADS)

    Leroy, Philippe; Li, Shuai; Jougnot, Damien; Revil, André; Wu, Yuxin

    2017-01-01

    SUMMARYWhen pH and alkalinity increase, <span class="hlt">calcite</span> frequently precipitates and hence modifies the petrophysical properties of porous media. The complex conductivity method can be used to directly monitor <span class="hlt">calcite</span> precipitation in porous media because it is sensitive to the evolution of the mineralogy, pore structure and its connectivity. We have developed a mechanistic grain polarization model considering the electrochemical polarization of the Stern and diffuse layer surrounding <span class="hlt">calcite</span> particles. Our complex conductivity model depends on the surface charge density of the Stern layer and on the electrical potential at the onset of the diffuse layer, which are computed using a basic Stern model of the <span class="hlt">calcite</span>/water interface. The complex conductivity measurements of Wu et al. (2010) on a column packed with glass beads where <span class="hlt">calcite</span> precipitation occurs are reproduced by our surface complexation and complex conductivity models. The evolution of the size and shape of <span class="hlt">calcite</span> particles during the <span class="hlt">calcite</span> precipitation experiment is estimated by our complex conductivity model. At the early stage of the <span class="hlt">calcite</span> precipitation experiment, modeled particles sizes increase and <span class="hlt">calcite</span> particles flatten with time because <span class="hlt">calcite</span> <span class="hlt">crystals</span> nucleate at the surface of glass beads and grow into larger <span class="hlt">calcite</span> grains around glass beads. At the later stage of the <span class="hlt">calcite</span> precipitation experiment, modeled sizes and cementation exponents of <span class="hlt">calcite</span> particles decrease with time because large <span class="hlt">calcite</span> grains aggregate over multiple glass beads, a percolation threshold is achieved, and small and discrete <span class="hlt">calcite</span> <span class="hlt">crystals</span> polarize.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA245645','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA245645"><span>Defects in <span class="hlt">Calcite</span>.</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1991-05-13</p> <p>AD-A245 645 A TRIDENT SCHOLAR PROJECT REPORT NO. 181 "DEFECTS IN <span class="hlt">CALCITE</span> " DTTC %N FEB 5-1912 UNITED STATES NAVAL ACADEMY ANNAPOLIS, MARYLAND 92-02841...report; no. 181 (1991) "DEFECTS IN <span class="hlt">CALCITE</span> " A Trident Scholar Project Report by Midshipman Anthony J. Kotarski, Class of 1991 U. S. Naval Academy Annapolis...REPORT TYPE AND DATES COVERED 13 May 1991 Final 1990/91 . TITLE AND SUBTITLE s. FUNDING NUMBERS DEFECTS IN <span class="hlt">CALCITE</span> 6. AUTHOR(S) Anthony J. Kotarski 7</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/3564','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/3564"><span>Diffusion of Ca and Mg in <span class="hlt">Calcite</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Cygan, R.T.; Fisler, D.K.</p> <p>1999-02-10</p> <p>The self-diffusion of Ca and the tracer diffusion of Mg in <span class="hlt">calcite</span> have been experimentally measured using isotopic tracers of {sup 25}Mg and {sup 44}Ca. Natural single <span class="hlt">crystals</span> of <span class="hlt">calcite</span> were coated with a thermally-sputtered oxide thin film and then annealed in a CO{sub 2} gas at one atmosphere total pressure and temperatures from 550 to 800 C. Diffusion coefficient values were derived from the depth profiles obtained by ion microprobe analysis. The resultant activation energies for Mg tracer diffusion and Ca self-diffusion are respectively: E{sub a}(Mg) = 284 {+-} 74 kJ/mol and E{sub a}(Ca) = 271 {+-} 80 kJ/mol. For the temperature ranges in these experiments, the diffusion of Mg is faster than Ca. The results are generally consistent in magnitude with divalent cation diffusion rates obtained in previous studies and provide a means of interpreting the thermal histories of carbonate minerals, the mechanism of dolomitization, and other diffusion-controlled processes. The results indicate that cation diffusion in <span class="hlt">calcite</span> is relatively slow and cations are the rate-limiting diffusing species for the deformation of <span class="hlt">calcite</span> and carbonate rocks. Application of the <span class="hlt">calcite</span>-dolomite geothermometer to metamorphic assemblages will be constrained by cation diffusion and cooling rates. The direct measurement of Mg tracer diffusion in <span class="hlt">calcite</span> indicates that dolomitization is unlikely to be accomplished by Mg diffusion in the solid state but by a recrystallization process.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27073032','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27073032"><span>Tailoring Zeolite ZSM-5 <span class="hlt">Crystal</span> Morphology/Porosity through Flexible Utilization of Silicalite-1 <span class="hlt">Seeds</span> as Templates: Unusual <span class="hlt">Crystallization</span> Pathways in a Heterogeneous System.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhang, Hongbin; Zhao, Yang; Zhang, Hongxia; Wang, Peicheng; Shi, Zhangping; Mao, Jianjiang; Zhang, Yahong; Tang, Yi</p> <p>2016-05-17</p> <p>Diffusion limitation in micropores of zeolites leads to a demand for optimization of zeolite morphology and/or porosity. However, tailoring <span class="hlt">crystallization</span> processes to realize targeted morphology/porosity is a major challenge in zeolite synthesis. On the basis of previous work on the salt-aided, <span class="hlt">seed</span>-induced route, the template effect of <span class="hlt">seeds</span> on the formation of micropores, mesopores and even macropores was further explored to selectively achieve desired hierarchical architectures. By carefully investigating the <span class="hlt">crystallization</span> processes of two typical samples with distinct <span class="hlt">crystal</span> morphologies, namely, 1) nanocrystallite-oriented self-assembled ZSM-5 zeolite and 2) enriched intracrystal mesoporous ZSM-5 zeolite, a detailed mechanism is proposed to clarify the role of silicalite-1 <span class="hlt">seeds</span> in the formation of diverse morphologies in a salt-rich heterogeneous system, combined with the transformation of <span class="hlt">seed</span>-embedded aluminosilicate gel. On the basis of these conclusions, the morphologies/porosities of products were precisely tailored by deliberately adjusting the synthesis parameters (KF/Si, tetrapropylammonium bromide/Si and H2 O/Si ratios and type of organic template) to regulate the kinetics of <span class="hlt">seed</span> dissolution and <span class="hlt">seed</span>-induced recrystallization. This work may not only provide a practical route to control zeolite <span class="hlt">crystallization</span> for tailoring <span class="hlt">crystal</span> morphology, but also expands the knowledge of <span class="hlt">crystal</span> growth mechanisms in a heterogeneous system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18084088','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18084088"><span><span class="hlt">Crystallization</span> and initial crystallographic characterization of a vicilin-type <span class="hlt">seed</span> storage protein from Pinus koraiensis.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Jin, Tengchuan; Fu, Tong Jen; Kothary, Mahendra H; Howard, Andrew; Zhang, Yu Zhu</p> <p>2007-12-01</p> <p>The cupin superfamily of proteins includes the 7S and 11S <span class="hlt">seed</span> storage proteins. Many members of this family of proteins are known allergens. In this study, the Korean pine (Pinus koraiensis) vicilin-type 7S <span class="hlt">seed</span> storage protein was isolated from defatted pine-nut extract and purified by sequential gel-filtration and anion-exchange chromatography. Well diffracting single <span class="hlt">crystals</span> were obtained by the vapor-diffusion method in hanging drops. The <span class="hlt">crystals</span> belong to the primitive cubic space group P2(1)3, with unit-cell parameters a = b = c = 148.174 A. Two vicilin molecules were present in the asymmetric unit and the Matthews coefficient was determined to be 2.90 A(3) Da(-1), with a corresponding solvent content of approximately 58%. A molecular-replacement structural solution has been obtained using the program Phaser. Refinement of the structure is currently under way.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2664755','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2664755"><span>Isolation, purification, <span class="hlt">crystallization</span> and preliminary crystallographic studies of chitinase from tamarind (Tamarindus indica) <span class="hlt">seeds</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Patil, Dipak N.; Datta, Manali; Chaudhary, Anshul; Tomar, Shailly; Kumar Sharma, Ashwani; Kumar, Pravindra</p> <p>2009-01-01</p> <p>A protein with chitinase activity has been isolated and purified from tamarind (Tamarindus indica) <span class="hlt">seeds</span>. N-terminal amino-acid sequence analysis of this protein confirmed it to be an ∼34 kDa endochitinase which belongs to the acidic class III chitinase family. The protein was <span class="hlt">crystallized</span> by the vapour-diffusion method using PEG 4000. The <span class="hlt">crystals</span> belonged to the tetragonal space group P41, with two molecules per asymmetric unit. Diffraction data were collected to a resolution of 2.6 Å. PMID:19342775</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19980038145','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19980038145"><span><span class="hlt">Seeded</span> Physical Vapor Transport of Cadmium-Zinc Telluride <span class="hlt">Crystals</span>: Growth and Characterization</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Palosz, W.; George, M. A.; Collins, E. E.; Chen, K.-T.; Zhang, Y.; Burger, A.</p> <p>1997-01-01</p> <p><span class="hlt">Crystals</span> of Cd(1-x)Zn(x)Te with x = 0.2 and 40 g in weight were grown on monocrystalline cadmium-zinc telluride <span class="hlt">seeds</span> by closed-ampoule physical vapor transport with or without excess (Cd + Zn) in the vapor phase. Two post-growth cool-down rates were used. The <span class="hlt">crystals</span> were characterized using low temperature photoluminescence, atomic force microscopy, chemical etching, X-ray diffraction and electrical measurements. No formation of a second, ZnTe-rich phase was observed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/870867','DOE-PATENT-XML'); return false;" href="http://www.osti.gov/scitech/servlets/purl/870867"><span><span class="hlt">Seed</span> <span class="hlt">crystals</span> with improved properties for melt processing superconductors for practical applications</span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Veal, Boyd W.; Paulikas, Arvydas; Balachandran, Uthamalingam; Zhong, Wei</p> <p>1997-01-01</p> <p>A method of fabricating bulk superconducting material including RBa.sub.2 Cu.sub.3 O.sub.7-.delta. comprising heating compressed powder oxides and/or carbonates of R and Ba and Cu present in mole ratios to form RBa.sub.2 Cu.sub.3 O.sub.7-.delta. in physical contact with an oxide single <span class="hlt">crystal</span> <span class="hlt">seed</span> to a temperature sufficient to form a liquid phase in the RBa.sub.2 Cu.sub.3 O.sub.7-.delta. while maintaining the single <span class="hlt">crystal</span> <span class="hlt">seed</span> solid to grow the superconducting material and thereafter cooling to provide a material including RBa.sub.2 Cu.sub.3 O.sub.7-.delta.. R is a rare earth or Y or La and the single <span class="hlt">crystal</span> <span class="hlt">seed</span> has a lattice mismatch with RBa.sub.2 Cu.sub.3 O.sub.7-.delta. of less than about 2% at the growth temperature. The starting material may be such that the final product contains a minor amount of R.sub.2 BaCuO.sub.5.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/458588','DOE-PATENT-XML'); return false;" href="http://www.osti.gov/scitech/biblio/458588"><span><span class="hlt">Seed</span> <span class="hlt">crystals</span> with improved properties for melt processing superconductors for practical applications</span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Veal, B.W.; Paulikas, A.; Balachandran, U.; Zhong, W.</p> <p>1997-03-18</p> <p>A method of fabricating bulk superconducting material is disclosed including RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} comprising heating compressed powder oxides and/or carbonates of R and Ba and Cu present in mole ratios to form RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} in physical contact with an oxide single <span class="hlt">crystal</span> <span class="hlt">seed</span> to a temperature sufficient to form a liquid phase in the RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} while maintaining the single <span class="hlt">crystal</span> <span class="hlt">seed</span> solid to grow the superconducting material and thereafter cooling to provide a material including RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}. R is a rare earth or Y or La and the single <span class="hlt">crystal</span> <span class="hlt">seed</span> has a lattice mismatch with RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} of less than about 2% at the growth temperature. The starting material may be such that the final product contains a minor amount of R{sub 2}BaCuO{sub 5}.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19191448','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19191448"><span>Development of a versatile high temperature top <span class="hlt">seeded</span> solution growth unit for growing cesium lithium borate <span class="hlt">crystals</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Reddy, Babu; Elizabeth, Suja; Bhat, H L; Karnal, A K</p> <p>2009-01-01</p> <p>The design and fabrication of a state of the art high temperature top <span class="hlt">seeded</span> solution growth (HTTSSG) unit with <span class="hlt">seed</span> and crucible rotation options is discussed. <span class="hlt">Crystals</span> from solid solutions of high viscosity could be grown using the setup. The fabricated setup is used to grow high optical quality single <span class="hlt">crystals</span> of cesium lithium borate with dimensions 50x40x40 mm(3) for frequency conversion of ir to UV laser through harmonic generation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhRvL.113y4801L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhRvL.113y4801L"><span>Demonstration of Single-<span class="hlt">Crystal</span> Self-<span class="hlt">Seeded</span> Two-Color X-Ray Free-Electron Lasers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lutman, A. A.; Decker, F.-J.; Arthur, J.; Chollet, M.; Feng, Y.; Hastings, J.; Huang, Z.; Lemke, H.; Nuhn, H.-D.; Marinelli, A.; Turner, J. L.; Wakatsuki, S.; Welch, J.; Zhu, D.</p> <p>2014-12-01</p> <p>A scheme for generating two simultaneous hard-x-ray free-electron laser pulses with a controllable difference in photon energy is described and then demonstrated using the self-<span class="hlt">seeding</span> setup at the Linac Coherent Light Source (LCLS). The scheme takes advantage of the existing LCLS equipment, which allows two independent rotations of the self-<span class="hlt">seeding</span> diamond <span class="hlt">crystal</span>. The two degrees of freedom are used to select two nearby <span class="hlt">crystal</span> reflections, causing two wavelengths to be present in the forward transmitted <span class="hlt">seeding</span> x-ray pulse. The free-electron laser system must support amplification at both desired wavelengths.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19863387','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19863387"><span>In vitro regulation of CaCO(3) <span class="hlt">crystal</span> growth by the highly acidic proteins of <span class="hlt">calcitic</span> sclerites in soft coral, Sinularia Polydactyla.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rahman, M Azizur; Oomori, Tamotsu</p> <p>2009-01-01</p> <p>Acidic proteins are generally thought to control mineral formation and growth in biocalcification. Analysis of proteinaceous components in the soluble and insoluble matrix fractions of sclerites in Sinularia polydactyla indicates that aspartic acid composes about 60% of the insoluble and 29% of the soluble matrix fractions. We previously analyzed aspartic acids in the matrix fractions (insoluble = 17 mol%; soluble = 38 mol%) of sclerites from a different type of soft coral, Lobophytum crassum, which showed comparatively lower aspartic acid-rich proteins than S. polydactyla. Thus, characterization of highly acidic proteins in the organic matrix of present species is an important first step toward linking function to individual proteins in soft coral. Here, we show that aspartic-acid rich proteins can control the CaCO(3) polymorph in vitro. The CaCO(3) precipitates in vitro in the presence of aspartic acid-rich proteins and 50 mM Mg(2+) was verified by Raman microprobe analysis. The matrix proteins of sclerites demonstrated that the aspartic-acid rich domain is crucial for the <span class="hlt">calcite</span> precipitation in soft corals. The crystalline form of CaCO(3) in the presence of aspartic acid-rich proteins in vitro was identified by X-ray diffraction and, revealed <span class="hlt">calcitic</span> polymorphisms with a strong (104) reflection. The structure of soft coral organic matrices containing aspartate-rich proteins and polysaccharides was assessed by Fourier transform infrared spectroscopy. These results strongly suggest that the aspartic acid-rich proteins within the organic matrix of soft corals play a key role in biomineralization regulation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22356065','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22356065"><span><span class="hlt">Crystallization</span> and preliminary X-ray diffraction analysis of a lectin from Canavalia maritima <span class="hlt">seeds</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Almeida Gadelha, Carlos Alberto de; Moreno, Frederico Bruno Mendes Batista; Santi-Gadelha, Tatiane; Cajazeiras, João Batista; Rocha, Bruno Anderson M. da; Rustiguel, Joane Kathelen Rodrigues; Freitas, Beatriz Tupinamba; Canduri, Fernanda; Delatorre, Plínio; Azevedo, Walter Filgueira Jr de; Cavada, Benildo S.</p> <p>2005-01-01</p> <p>A lectin from C. maritima was <span class="hlt">crystallized</span> using the vapour-diffusion method and <span class="hlt">crystals</span> diffracted to 2.1 Å resolution. A molecular-replacement search found a solution with a correlation coefficient of 69.2% and an R factor of 42.5%, refinement is in progress. A lectin from Canavalia maritima <span class="hlt">seeds</span> (ConM) was purified and submitted to <span class="hlt">crystallization</span> experiments. The best <span class="hlt">crystals</span> were obtained using the vapour-diffusion method at a constant temperature of 293 K and grew in 7 d. A complete structural data set was collected to 2.1 Å resolution using a synchrotron-radiation source. The ConM <span class="hlt">crystal</span> belongs to the orthorhombic space group P2{sub 1}2{sub 1}2, with unit-cell parameters a = 67.15, b = 70.90, c = 97.37 Å. A molecular-replacement search found a solution with a correlation coefficient of 69.2% and an R factor of 42.5%. Crystallographic refinement is under way.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999JCrGr.200..251B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999JCrGr.200..251B"><span>The kinetics of desilication of synthetic spent Bayer liquor <span class="hlt">seeded</span> with cancrinite and cancrinite/sodalite mixed-phase <span class="hlt">crystals</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Barnes, Mark C.; Addai-Mensah, Jonas; Gerson, Andrea R.</p> <p>1999-04-01</p> <p>Isothermal, batch desilication kinetics of synthetic, sodium aluminate solution (spent Bayer liquor) via cancrinite and cancrinite/sodalite mixed-phase <span class="hlt">crystal</span> growth, have been studied under conditions at which sodium aluminosilicate scale forms at the surfaces of steel heat exchangers of alumina plant. <span class="hlt">Seeding</span> with the pure cancrinite and mixed-phase <span class="hlt">crystals</span> results in the suppression of scale formation and a faster rate of liquor desilication in comparison with its sodalite dimorph. Cancrinite <span class="hlt">seed</span> <span class="hlt">crystals</span> prepared from NO -3-rich solutions exhibited <span class="hlt">crystal</span> growth mechanism and kinetic behaviour different from dimorphic mixed-phase <span class="hlt">crystals</span> prepared from CO 2-3-rich solutions, when both were used to desilicate CO 2-3-rich spent Bayer liquor. The rate of desilication due to <span class="hlt">crystal</span> growth on CO 2-3-cancrinite/sodalite mixed phase <span class="hlt">crystals</span> followed a second-order dependence on the relative supersaturation of SiO 2. An activation energy of 52 kJ mol -1 was estimated for the <span class="hlt">crystal</span> growth process. For desilication kinetics involving NO -3-cancrinite <span class="hlt">seed</span> <span class="hlt">crystal</span> growth, a third-order dependence on relative supersaturation of SiO 2 and an activation energy of 63 kJ mol -1 were obtained.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011JCrGr.324..177A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011JCrGr.324..177A"><span>Extracellular matrix protein in calcified endoskeleton: a potential additive for <span class="hlt">crystal</span> growth and design</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Azizur Rahman, M.; Fujimura, Hiroyuki; Shinjo, Ryuichi; Oomori, Tamotsu</p> <p>2011-06-01</p> <p>In this study, we demonstrate a key function of extracellular matrix proteins (ECMPs) on <span class="hlt">seed</span> <span class="hlt">crystals</span>, which are isolated from calcified endoskeletons of soft coral and contain only CaCO 3 without any living cells. This is the first report that an ECMP protein extracted from a marine organism could potentially influence in modifying the surface of a substrate for designing materials via <span class="hlt">crystallization</span>. We previously studied with the ECMPs from a different type of soft coral ( Sinularia polydactyla) without introducing any <span class="hlt">seed</span> <span class="hlt">crystals</span> in the process , which showed different results. Thus, <span class="hlt">crystallization</span> on the <span class="hlt">seed</span> in the presence of ECMPs of present species is an important first step toward linking function to individual proteins from soft coral. For understanding this interesting phenomenon, in vitro <span class="hlt">crystallization</span> was initiated in a supersaturated solution on <span class="hlt">seed</span> particles of <span class="hlt">calcite</span> (1 0 4) with and without ECMPs. No change in the <span class="hlt">crystal</span> growth shape occurred without ECMPs present during the <span class="hlt">crystallization</span> process. However, with ECMPs, the morphology and phase of the <span class="hlt">crystals</span> in the <span class="hlt">crystallization</span> process changed dramatically. Upon completion of <span class="hlt">crystallization</span> with ECMPs, an attractive <span class="hlt">crystal</span> morphology was found. Scanning electron microscopy (SEM) was utilized to observe the <span class="hlt">crystal</span> morphologies on the <span class="hlt">seeds</span> surface. The mineral phases of <span class="hlt">crystals</span> nucleated by ECMPs on the <span class="hlt">seeds</span> surface were examined by Raman spectroscopy. Although 50 mM Mg 2+ is influential in making aragonite in the <span class="hlt">crystallization</span> process, the ECMPs significantly made <span class="hlt">calcite</span> <span class="hlt">crystals</span> even when 50 mM Mg 2+ was present in the process. <span class="hlt">Crystallization</span> with the ECMP additive seems to be a technically attractive strategy to generate assembled micro <span class="hlt">crystals</span> that could be used in <span class="hlt">crystals</span> growth and design in the Pharmaceutical and biotechnology industries.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA008043','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA008043"><span>Production Engineering for Growth of Synthetic <span class="hlt">Calcite</span> Polarizer Material</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1974-08-01</p> <p>AD-A008 043 PRODUCTION ENGINEERING FOR GROWTH OF SYNTHETIC <span class="hlt">CALCITE</span> POLARIZER MATERIAL Roger F. Belt, et al Litton Systems...Production Bngin««ring for Growth of Synthetic <span class="hlt">Calcit</span> « Polarizer Material I. RCCIPItNT’tCATALOO NUMMN i. T.vpc or ncpoMT • rtmoo covtnto Final Report...VOKOt (CanlliMit en »xift •id« II ntffrt Kid Idtnlllr br block iwmbmr) <span class="hlt">Crystal</span> Growth Hydrothermal Growth <span class="hlt">Calcite</span> Polarizers 30. AtSTHACT</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1033795','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1033795"><span>Improving the diffraction of full-length human selenomethionyl metavinculin <span class="hlt">crystals</span> by streak-<span class="hlt">seeding</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Rangarajan, Erumbi S.; Izard, Tina</p> <p>2012-06-28</p> <p>Metavinculin is an alternatively spliced isoform of vinculin that has a 68-residue insert in its tail domain (1134 total residues) and is exclusively expressed in cardiac and smooth muscle tissue, where it plays important roles in myocyte adhesion complexes. Mutations in the metavinculin-specific insert are associated with dilated cardiomyopathy (DCM) in man. <span class="hlt">Crystals</span> of a DCM-associated mutant of full-length selenomethionine-labeled metavinculin grown by hanging-drop vapor diffusion diffracted poorly and were highly sensitive to radiation, preventing the collection of a complete X-ray diffraction data set at the highest possible resolution. Streak-<span class="hlt">seeding</span> markedly improved the stability, <span class="hlt">crystal</span>-growth rate and diffraction quality of DCM-associated mutant metavinculin <span class="hlt">crystals</span>, allowing complete data collection to 3.9 {angstrom} resolution. These <span class="hlt">crystals</span> belonged to space group P4{sub 3}2{sub 1}2, with two molecules in the asymmetric unit and unit-cell parameters a = b = 170, c = 211 {angstrom}, {alpha} = {beta} = {gamma} = 90{sup o}.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23220770','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23220770"><span>Micro-CT observations of the 3D distribution of calcium oxalate <span class="hlt">crystals</span> in cotyledons during maturation and germination in Lotus miyakojimae <span class="hlt">seeds</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Yamauchi, Daisuke; Tamaoki, Daisuke; Hayami, Masato; Takeuchi, Miyuki; Karahara, Ichirou; Sato, Mayuko; Toyooka, Kiminori; Nishioka, Hiroshi; Terada, Yasuko; Uesugi, Kentaro; Takano, Hidekazu; Kagoshima, Yasushi; Mineyuki, Yoshinobu</p> <p>2013-06-01</p> <p>The cotyledon of legume <span class="hlt">seeds</span> is a storage organ that provides nutrients for <span class="hlt">seed</span> germination and seedling growth. The spatial and temporal control of the degradation processes within cotyledons has not been elucidated. Calcium oxalate (CaOx) <span class="hlt">crystals</span>, a common calcium deposit in plants, have often been reported to be present in legume <span class="hlt">seeds</span>. In this study, micro-computed tomography (micro-CT) was employed at the SPring-8 facility to examine the three-dimensional distribution of <span class="hlt">crystals</span> inside cotyledons during <span class="hlt">seed</span> maturation and germination of Lotus miyakojimae (previously Lotus japonicus accession Miyakojima MG-20). Using this technique, we could detect the outline of the embryo, void spaces in <span class="hlt">seeds</span> and the cotyledon venation pattern. We found several sites that strongly inhibited X-ray transmission within the cotyledons. Light and polarizing microscopy confirmed that these areas corresponded to CaOx <span class="hlt">crystals</span>. Three-dimensional observations of dry <span class="hlt">seeds</span> indicated that the CaOx <span class="hlt">crystals</span> in the L. miyakojimae cotyledons were distributed along lateral veins; however, their distribution was limited to the abaxial side of the procambium. The CaOx <span class="hlt">crystals</span> appeared at stage II (<span class="hlt">seed</span>-filling stage) of <span class="hlt">seed</span> development, and their number increased in dry <span class="hlt">seeds</span>. The number of <span class="hlt">crystals</span> in cotyledons was high during germination, suggesting that CaOx <span class="hlt">crystals</span> are not degraded for their calcium supply. Evidence for the conservation of CaOx <span class="hlt">crystals</span> in cotyledons during the L. miyakojimae germination process was also supported by the biochemical measurement of oxalic acid levels.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li class="active"><span>6</span></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_6 --> <div id="page_7" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="121"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22356421','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22356421"><span>Combining site-specific mutagenesis and <span class="hlt">seeding</span> as a strategy to <span class="hlt">crystallize</span> ‘difficult’ proteins: the case of Staphylococcus aureus thioredoxin</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Roos, Goedele; Brosens, Elke; Wahni, Khadija; Desmyter, Aline; Spinelli, Silvia; Wyns, Lode; Messens, Joris; Loris, Remy</p> <p>2006-12-01</p> <p>S. aureus thioredoxin was <span class="hlt">crystallized</span> using a combination of <span class="hlt">seeding</span> and site-specific mutagenesis. The P31T mutant of Staphylococcus aureus thioredoxin <span class="hlt">crystallizes</span> spontaneously in space group P2{sub 1}2{sub 1}2{sub 1}, with unit-cell parameters a = 41.7, b = 49.5, c = 55.6 Å. The <span class="hlt">crystals</span> diffract to 2.2 Å resolution. Isomorphous <span class="hlt">crystals</span> of wild-type thioredoxin as well as of other point mutants only grow when <span class="hlt">seeded</span> with the P31T mutant. These results suggest <span class="hlt">seeding</span> as a valuable tool complementing surface engineering for proteins that are hard to <span class="hlt">crystallize</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25533590','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25533590"><span>Interaction of alcohols with the <span class="hlt">calcite</span> surface.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bovet, N; Yang, M; Javadi, M S; Stipp, S L S</p> <p>2015-02-07</p> <p>A clearer understanding of <span class="hlt">calcite</span> interactions with organic molecules would contribute to a range of fields including harnessing the secrets of biomineralisation where organisms produce hard parts, increasing oil production from spent reservoirs, remediating contaminated soils and drinking water aquifers and improving manufacturing methods for industrial products such as pigments, soft abrasives, building materials and optical devices. Biomineralisation by some species of blue green algae produces beautifully elaborate platelets of <span class="hlt">calcite</span> where the individual <span class="hlt">crystals</span> are of nanometer scale. Controlling their growth requires complex polysaccharides. Polysaccharide activity depends on the functionality of OH groups, so to simplify the system in order to get closer to a molecular level understanding, we investigated the interaction of OH from a suite of alcohols with clean, freshly cleaved <span class="hlt">calcite</span> surfaces. X-ray photoelectron spectroscopy (XPS) provided binding energies and revealed the extent of surface coverage. Molecular dynamics (MD) simulations supplemented with information about molecule ordering, orientation and packing density. The results show that all alcohols studied bond with the <span class="hlt">calcite</span> surface through the OH group, with their carbon chains sticking away in a standing-up orientation. Alcohol molecules are closely packed and form a well-ordered monolayer on the surface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2344101','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2344101"><span><span class="hlt">Crystallization</span> and initial crystallographic characterization of a vicilin-type <span class="hlt">seed</span> storage protein from Pinus koraiensis</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Jin, Tengchuan; Fu, Tong-Jen; Kothary, Mahendra H.; Howard, Andrew; Zhang, Yu-Zhu</p> <p>2007-01-01</p> <p>The cupin superfamily of proteins includes the 7S and 11S <span class="hlt">seed</span> storage proteins. Many members of this family of proteins are known allergens. In this study, the Korean pine (Pinus koraiensis) vicilin-type 7S <span class="hlt">seed</span> storage protein was isolated from defatted pine-nut extract and purified by sequential gel-filtration and anion-exchange chromatography. Well diffracting single <span class="hlt">crystals</span> were obtained by the vapor-diffusion method in hanging drops. The <span class="hlt">crystals</span> belong to the primitive cubic space group P213, with unit-cell parameters a = b = c = 148.174 Å. Two vicilin molecules were present in the asymmetric unit and the Matthews coefficient was determined to be 2.90 Å3 Da−1, with a corresponding solvent content of ∼58%. A molecular-replacement structural solution has been obtained using the program Phaser. Refinement of the structure is currently under way. PMID:18084088</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24328105','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24328105"><span><span class="hlt">Crystal</span> structure of Korean pine (Pinus koraiensis) 7S <span class="hlt">seed</span> storage protein with copper ligands.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Jin, Tengchuan; Wang, Yang; Chen, Yu-Wei; Fu, Tong-Jen; Kothary, Mahendra H; McHugh, Tara H; Zhang, Yuzhu</p> <p>2014-01-08</p> <p>The prevalence of food allergy has increased in recent years, and Korean pine vicilin is a potential food allergen. We have previously reported the <span class="hlt">crystallization</span> of Korean pine vicilin purified from raw pine nut. Here we report the isolation of vicilin mRNA and the <span class="hlt">crystal</span> structure of Korean pine vicilin at 2.40 Å resolution. The overall structure of pine nut vicilin is similar to the structures of other 7S <span class="hlt">seed</span> storage proteins and consists of an N-terminal domain and a C-terminal domain. Each assumes a cupin fold, and they are symmetrically related about a pseudodyad axis. Three vicilin molecules form a doughnut-shaped trimer through head-to-tail association. Structure characterization of Korean pine nut vicilin unexpectedly showed that, in its native trimeric state, the vicilin has three copper ligands. Sequence alignments suggested that the copper-coordinating residues were conserved in winter squash, sesame, tomato, and several tree nuts, while they were not conserved in a number of legumes, including peanut and soybean. Additional studies are needed to assess whether the copper-coordinating property of vicilins has a biological function in the relevant plants. The nutritional value of this copper-coordinating protein in tree nuts and other edible <span class="hlt">seeds</span> may be worth further investigations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JChPh.145h4702F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JChPh.145h4702F"><span>Anisotropic parallel self-diffusion coefficients near the <span class="hlt">calcite</span> surface: A molecular dynamics study</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Franco, Luís F. M.; Castier, Marcelo; Economou, Ioannis G.</p> <p>2016-08-01</p> <p>Applying classical molecular dynamics simulations, we calculate the parallel self-diffusion coefficients of different fluids (methane, nitrogen, and carbon dioxide) confined between two { 10 1 ¯ 4 } <span class="hlt">calcite</span> <span class="hlt">crystal</span> planes. We have observed that the molecules close to the <span class="hlt">calcite</span> surface diffuse differently in distinct directions. This anisotropic behavior of the self-diffusion coefficient is investigated for different temperatures and pore sizes. The ion arrangement in the <span class="hlt">calcite</span> <span class="hlt">crystal</span> and the strong interactions between the fluid particles and the <span class="hlt">calcite</span> surface may explain the anisotropy in this transport property.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27586936','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27586936"><span>Anisotropic parallel self-diffusion coefficients near the <span class="hlt">calcite</span> surface: A molecular dynamics study.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Franco, Luís F M; Castier, Marcelo; Economou, Ioannis G</p> <p>2016-08-28</p> <p>Applying classical molecular dynamics simulations, we calculate the parallel self-diffusion coefficients of different fluids (methane, nitrogen, and carbon dioxide) confined between two {101̄4} <span class="hlt">calcite</span> <span class="hlt">crystal</span> planes. We have observed that the molecules close to the <span class="hlt">calcite</span> surface diffuse differently in distinct directions. This anisotropic behavior of the self-diffusion coefficient is investigated for different temperatures and pore sizes. The ion arrangement in the <span class="hlt">calcite</span> <span class="hlt">crystal</span> and the strong interactions between the fluid particles and the <span class="hlt">calcite</span> surface may explain the anisotropy in this transport property.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.6903M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.6903M"><span>Microstructures and elastic properties of sheared <span class="hlt">calcite</span> flowstone</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mitrovic, Ivanka; Grasemann, Bernhard; Plan, Lukas; Tesei, Telemaco; Baron, Ivo</p> <p>2016-04-01</p> <p>Flowstone is a monomineralic rock precipitated along cave walls and floors, composed of columnar centimeter-scale <span class="hlt">calcite</span> <span class="hlt">crystals</span> with strong growth orientation perpendicular to the growth surface. Broken and scratched flowstone can serve as evidence for active faulting and has been found in several alpine caves in Austria. In order to understand the fault mechanics, and associated potential earthquake hazard, experimentally deformed flowstone is studied using microstructural analysis and EBSD-measured physical properties of <span class="hlt">calcite</span> <span class="hlt">crystals</span>. For that purpose, we have performed sliding experiments using a rock deformation biaxial apparatus on rectangular blocks of flowstone that were sheared perpendicular to the <span class="hlt">calcite</span> growth direction. The experiments were performed under room conditions, with sub-seismic sliding velocity (0.001-0.01 mm/s) and constant effective normal stress (3-10 MPa). The deformed samples show diverse brittle features, including high fracture density, the development of <span class="hlt">calcite</span>-rich fault gouge with Riedel shears within a foliated cataclasite, and drastic grain size reduction down to nm-scale grains. The dominant plastic microstructure is mechanical twinning. Due to the strong growth orientation of <span class="hlt">calcite</span> in flowstone, <span class="hlt">crystals</span> can be bent due to shearing. We examine the bending by applying orientation distribution, Schmid factor and elasticity tensor calculations using MTEX Toolbox from EBSD data. In this unique case the flowstone deformation experiments bridge the gap between single <span class="hlt">crystal</span> and rock powder experiments. This study is supported by the Austrian Science Foundation: SPELEOTECT project (P25884-N29).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeCoA.145...13R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeCoA.145...13R"><span>Physicochemical characteristics of drip waters: Influence on mineralogy and <span class="hlt">crystal</span> morphology of recent cave carbonate precipitates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Riechelmann, Sylvia; Schröder-Ritzrau, Andrea; Wassenburg, Jasper A.; Schreuer, Jürgen; Richter, Detlev K.; Riechelmann, Dana F. C.; Terente, Mihai; Constantin, Silviu; Mangini, Augusto; Immenhauser, Adrian</p> <p>2014-11-01</p> <p> corners of the <span class="hlt">crystal</span> <span class="hlt">seed</span>, (ii) <span class="hlt">crystal</span> habit tend to elongate along [0 0 1] due to slower growth of faces with high Mg2+ densities, (iii) reconstitution of <span class="hlt">crystal</span> faces with low Mg2+ densities, and (iv) occurrence of <span class="hlt">calcite</span> <span class="hlt">crystals</span> with bended faces and edges due to very high Mg2+ (Mg/Ca ratios of 0.009-0.051) incorporation. Growth rates and possibly also organic compounds, however, may also affect the morphology of <span class="hlt">calcite</span> <span class="hlt">crystals</span>. Based on the data shown here, the relation of Mg2+ incorporation and the resulting changes in <span class="hlt">calcite</span> <span class="hlt">crystal</span> morphologies as well as the conditions of aragonite precipitation are now clearly better understood. Further work should aim at linking the <span class="hlt">calcite</span> <span class="hlt">crystal</span> morphology of watch glass precipitates with <span class="hlt">calcite</span> <span class="hlt">crystal</span> fabrics in speleothems in order to exploit the petrographic archive of speleothem deposits.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFM.B12C0787D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFM.B12C0787D"><span>Sulfated Macromolecules as Templates for <span class="hlt">Calcite</span> Nucleation and Growth</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>David, M.; Passalacqua, K.; Neira, A. C.; Fernandez, M. S.</p> <p>2003-12-01</p> <p>Mineralization of egg and seashells is controlled by an intimate association of inorganic materials with organic macromolecules. Among them, particular polyanionic sulfated macromolecules referred to as proteoglycans have been described to be involved in the calcification of these biominerals. The sulfated moieties of the proteoglycans are part of polymer chains constituted of building-blocks of disaccharide units, referred to as sulfated glycosaminoglycans (GAGs), which are covalently attached to a protein core. By using a sitting drop <span class="hlt">crystallization</span> assay under controlled conditions of time, pH and reactants concentration, we have tested several sulfated and non-sulfated GAGs (i.e.: dermatan and keratan sulfate, hyaluronic acid and heparin), differing in their sulfonate and carboxylate degree and pattern, in their ability to modify calcium carbonate <span class="hlt">crystal</span> morphology as observed under scanning electron microscopy. Without the addition of GAGs, regular \\{104\\} rhombohedral <span class="hlt">calcite</span> <span class="hlt">crystals</span> were obtained. When hyaluronic acid (HA), a non-sulfated but carboxylated GAG, was added, 20 mm long piles of unmodified <span class="hlt">calcite</span> <span class="hlt">crystals</span> were observed. When desulfated dermatan, which is an epimeric form of HA but shorter polymer, having their carboxylate groups in an inverted configuration, was added, isolated rhombohedral \\{104\\} <span class="hlt">calcite</span> <span class="hlt">crystals</span> showing rounded corners with planes oriented parallel to the c axis were observed. When dermatan sulfated was added, isolated <span class="hlt">calcite</span> <span class="hlt">crystals</span> exhibit a columnar morphology as a \\{hk0\\} cylinder with three \\{104\\} faces forming a cap at both ends. Heparin activity depends on the fraction added. Fast-moving heparin fraction (FM), is an undersulfated, low-molecular-weight heterogeneous polymer, while slow-moving heparin fraction (SM) is an high-molecular-weight homogeneous polymer rich in trisulfated-disaccharide units. When FM was added, isolated <span class="hlt">calcite</span> <span class="hlt">crystals</span> displayed rhombohedrical \\{104\\} faces but flat corners of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000Geo....28..931M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000Geo....28..931M"><span>Unusual <span class="hlt">calcite</span> stromatolites and pisoids from a landfill leachate collection system</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Maliva, Robert G.; Missimer, Thomas M.; Leo, Kevin C.; Statom, Richard A.; Dupraz, Christophe; Lynn, Matthew; Dickson, J. A. D.</p> <p>2000-10-01</p> <p>Low-magnesium <span class="hlt">calcite</span> stromatolites and pisoids were found to have precipitated within the leachate collection system piping of a Palm Beach County, Florida, landfill. The stromatolites and pisoids formed in an aphotic and anoxic environment that was at times greatly supersaturated with <span class="hlt">calcite</span>. The stromatolites are composed of branching cylindrical bundles of concentrically laminated radial fibrous <span class="hlt">crystals</span>. The pisoids consist of concentric layers of radial fibrous and microcrystalline <span class="hlt">calcite</span>. Bacteria, likely sulfate reducing, appear to have acted as catalysts for <span class="hlt">calcite</span> <span class="hlt">crystal</span> nucleation, and thus the formation of the stromatolites and pisoids. The leachate system stromatolites provide a recent example of stromatolites that formed largely by cement precipitation. By acting as catalysts for <span class="hlt">calcite</span> nucleation, bacteria may cause more rapid cementation than would have occurred under purely abiotic conditions. Rapid <span class="hlt">calcite</span> precipitation catalyzed by bacteria has interfered with the operation of the Palm Beach County landfill leachate collection by obstructing pipes and may be an unrecognized problem at other landfill sites.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.A13H0289N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.A13H0289N"><span>The application of time-dependent ice <span class="hlt">crystal</span> trajectory and growth model for the evaluation of cloud <span class="hlt">seeding</span> experiment using liquid carbon dioxide</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nishiyama, K.; Wakimizu, K.; Maki, T.; Suzuki, Y.; Morita, O.; Tomine, K.</p> <p>2012-12-01</p> <p>This study evaluated the results of cloud <span class="hlt">seeding</span> experiment conducted on 17th January, 2008, in western Kyushu, Japan, using simplified time-dependent ice <span class="hlt">crystal</span> growth and trajectory cloud model, which is characterized by 1) depositional diffusion growth process only of an ice <span class="hlt">crystal</span>, and 2) the pursuit of the growing ice <span class="hlt">crystal</span> based on wind field and ice <span class="hlt">crystal</span> terminal velocity. For the estimation of the ice <span class="hlt">crystal</span> growth and trajectory, the model specifies ice supersaturation ratio that expresses the degree of competition growth among ice <span class="hlt">crystals</span> formed by LC <span class="hlt">seeding</span> for existing water vapor, assuming no effect of natural ice <span class="hlt">crystals</span>. The model is based on ice <span class="hlt">crystal</span> growth along a- and c-axes depending on air temperature and ice supersatuation, according to Chen and Lamb (1994). The cloud <span class="hlt">seeding</span> experiment was conducted by applying homogeneous nucleation (rapid cooling of air mass and subsequent formation of many ice <span class="hlt">crystals</span>~1013/g LC) of Liquid Carbon (LC) dioxide <span class="hlt">seeding</span> under typical winter-type snowfall-inducing weather situation characterized by the outbreak of cold air masses from the Siberia. The result of aircraft horizontally-penetrating <span class="hlt">seeding</span> of LC into lower layer (-2 degree C) of supercooled convective cloud with 1km thickness above the freezing level led to the formation of an artificially-induced 'isolated' radar echo (the left figures of Fig. 1) in dominant 'no-natural radar echo region'. In other words, natural biases were eliminated by the formation of the isolated radar echo. This fact provides the shortcut for evaluating the result of cloud <span class="hlt">seeding</span> experiment. In the next, the observed cloud <span class="hlt">seeding</span> results were evaluated by estimating the trajectory of artificially-induced growing ice <span class="hlt">crystal</span>. The results show that the trajectory of artificial ice <span class="hlt">crystals</span> depends on the degree of completion growth mode. Free growth brings rapid growth of an ice <span class="hlt">crystal</span> and, therefore, the ice <span class="hlt">crystal</span> falls into lower layers for a short time</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26505799','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26505799"><span><span class="hlt">Crystal</span> structure of mature 2S albumin from Moringa oleifera <span class="hlt">seeds</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ullah, Anwar; Mariutti, Ricardo Barros; Masood, Rehana; Caruso, Icaro Putinhon; Costa, Gustavo Henrique Gravatim; Millena de Freita, Cristhyane; Santos, Camila Ramos; Zanphorlin, Leticia Maria; Rossini Mutton, Márcia Justino; Murakami, Mario Tyago; Arni, Raghuvir Krishnaswamy</p> <p></p> <p>2S albumins, the <span class="hlt">seed</span> storage proteins, are the primary sources of carbon and nitrogen and are involved in plant defense. The mature form of Moringa oleifera (M. oleifera), a chitin binding protein isoform 3-1 (mMo-CBP3-1) a thermostable antifungal, antibacterial, flocculating 2S albumin is widely used for the treatment of water and is potentially interesting for the development of both antifungal drugs and transgenic crops. The <span class="hlt">crystal</span> structure of mMo-CBP3-1 determined at 1.7 Å resolution demonstrated that it is comprised of two proteolytically processed α-helical chains, stabilized by four disulfide bridges that is stable, resistant to pH changes and has a melting temperature (TM) of approximately 98 °C. The surface arginines and the polyglutamine motif are the key structural factors for the observed flocculating, antibacterial and antifungal activities. This represents the first <span class="hlt">crystal</span> structure of a 2S albumin and the model of the pro-protein indicates the structural changes that occur upon formation of mMo-CBP3-1 and determines the structural motif and charge distribution patterns for the diverse observed activities.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70018861','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70018861"><span>Chemistry and petrography of <span class="hlt">calcite</span> in the KTB pilot borehole, Bavarian Oberpfalz, Germany</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Komor, S.C.</p> <p>1995-01-01</p> <p>The KTB pilot borehole in northeast Bavaria, Germany, penetrates 4000 m of gneiss, amphibolite, and subordinate calc-silicate, lamprophyre and metagabbro. There are three types of <span class="hlt">calcite</span> in the drilled section: 1) metamorphic <span class="hlt">calcite</span> in calc-silicate and marble; 2) crack-filling <span class="hlt">calcite</span> in all lithologies; and 3) replacement <span class="hlt">calcite</span> in altered minerals. Crack-filling and replacement <span class="hlt">calcite</span> postdate metamorphic <span class="hlt">calcite</span>. Multiple <span class="hlt">calcite</span> generations in individual cracks suggest that different generations of water repeatedly flowed through the same cracks. Crack-filling mineral assemblages that include <span class="hlt">calcite</span> originally formed at temperatures of 150-350??C. Presently, crack-filling <span class="hlt">calcite</span> is in chemical and isotopic equilibrium with saline to brackish water in the borehole at temperatures of ???120??C. The saline to brackish water contains a significant proportion of meteoric water. Re-equilibration of crack-filling <span class="hlt">calcite</span> to lower temperatures means that <span class="hlt">calcite</span> chemistry tells us little about water-rock interactions in the <span class="hlt">crystal</span> section of temperatures higher than ~120??C. -from Author</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002AGUFM.B11B0728F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002AGUFM.B11B0728F"><span>Strontium Incorporation Into <span class="hlt">Calcite</span> Generated by Bacterial Ureolysis</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fujita, Y.; Ingram, J. A.; Cortez, M. M.; Redden, G. D.; Smith, R. W.</p> <p>2002-12-01</p> <p>Strontium incorporation into <span class="hlt">calcite</span> generated by bacterial ureolytic activity was investigated as part of a larger effort to evaluate the use of in situ urea hydrolysis for accelerating co-precipitation of trace metals and radionuclides in contaminated aquifers. 90Sr, a uranium fission product with a half-life of 29 years, is a significant subsurface contaminant at several Department of Energy facilities and could be immobilized using this remediation strategy. Experiments were conducted in a medium designed to simulate the groundwater of the Snake River Plain Aquifer in eastern Idaho, amended with strontium. Initially the solution was undersaturated with respect to <span class="hlt">calcite</span>. As a model ureolytic organism, we used Bacillus pasteurii, a well-characterized bacterium known for high urease activity and previously shown to induce <span class="hlt">calcite</span> precipitation in urea-amended medium. To gain information on the effect of the bacterial surfaces, we also looked at precipitation in the presence of a bacterial species that did not hydrolyze urea, as well as in the absence of bacteria. In the absence of bacterial ureolysis, carbonate precipitation was induced by addition of ammonium carbonate. All products were identified as <span class="hlt">calcite</span> by X-ray diffraction. Strontium uptake was observed in all cases, but was greatest in the system including bacterial ureolysis. Sputter depth element profiling by time-of-flight secondary ion mass spectrometry (TOF-SIMS) confirmed this finding, showing highest Sr:Ca ratios in the bacterially generated <span class="hlt">calcite</span> throughout the depth (~350 nm) investigated. Environmental Scanning Electron Microscopy (ESEM) of the solids revealed regular <span class="hlt">crystals</span> containing the outlines of embedded or entombed bacterial cells, suggesting that <span class="hlt">calcite</span> precipitated directly on the cell surfaces when present. Analysis by X-ray Absorption Near Edge Spectroscopy (XANES) indicated that in both the biotically and abiotically generated <span class="hlt">calcites</span> the Sr was incorporated into the <span class="hlt">calcite</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/980913','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/980913"><span>On the complex conductivity signatures of <span class="hlt">calcite</span> precipitation</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Wu, Yuxin; Hubbard, Susan; Williams, Kenneth Hurst; Ajo-Franklin, Jonathan</p> <p>2009-11-01</p> <p><span class="hlt">Calcite</span> is a mineral phase that frequently precipitates during subsurface remediation or geotechnical engineering processes. This precipitation can lead to changes in the overall behavior of the system, such as flow alternation and soil strengthening. Because induced <span class="hlt">calcite</span> precipitation is typically quite variable in space and time, monitoring its distribution in the subsurface is a challenge. In this research, we conducted a laboratory column experiment to investigate the potential of complex conductivity as a mean to remotely monitor <span class="hlt">calcite</span> precipitation. <span class="hlt">Calcite</span> precipitation was induced in a glass bead (3 mm) packed column through abiotic mixing of CaCl{sub 2} and Na{sub 2}CO{sub 3} solutions. The experiment continued for 12 days with a constant precipitation rate of {approx}0.6 milimole/d. Visual observations and scanning electron microscopy imaging revealed two distinct phases of precipitation: an earlier phase dominated by well distributed, discrete precipitates and a later phase characterized by localized precipitate aggregation and associated pore clogging. Complex conductivity measurements exhibited polarization signals that were characteristic of both phases of <span class="hlt">calcite</span> precipitation, with the precipitation volume and <span class="hlt">crystal</span> size controlling the overall polarization magnitude and relaxation time constant. We attribute the observed responses to polarization at the electrical double layer surrounding <span class="hlt">calcite</span> <span class="hlt">crystals</span>. Our experiment illustrates the potential of electrical methods for characterizing the distribution and aggregation state of nonconductive minerals like <span class="hlt">calcite</span>. Advancing our ability to quantify geochemical transformations using such noninvasive methods is expected to facilitate our understanding of complex processes associated with natural subsurface systems as well as processes induced through engineered treatments (such as environmental remediation and carbon sequestration).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16233632','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16233632"><span>Gamma-linolenic acid enrichment from Borago officinalis and Echium fastuosum <span class="hlt">seed</span> oils and fatty acids by low temperature <span class="hlt">crystallization</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>López-Martínez, Juan Carlos; Campra-Madrid, Pablo; Guil-Guerrero, José Luis</p> <p>2004-01-01</p> <p>Solvent winterization of <span class="hlt">seed</span> oil and free fatty acids (FFAs) was employed to obtain gamma-linolenic acid (GLA; 18:3omega6) concentrates from <span class="hlt">seed</span> oils of two Boraginaceae species, Echium fastuosum and Borago officinalis. Different solutions of <span class="hlt">seed</span> oils and FFAs from these two oils at 10%, 20% and 40% (w/w) were <span class="hlt">crystallized</span> at 4 degrees C, -24 degrees C and -70 degrees C, respectively, using hexane, acetone, diethyl ether, isobutanol and ethanol as solvents. Best results were obtained for B. officinalis FFAs in hexane, reaching a maximum GLA concentration of 58.8% in the liquid fraction (LF). In E. fastuosum, the highest GLA concentration (39.9%) was also achieved with FFAs in hexane.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/289451','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/289451"><span>Atomistic simulation of the differences between <span class="hlt">calcite</span> and dolomite surfaces</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Titiloye, J.O.; Leeuw, N.H. de; Parker, S.C.</p> <p>1998-08-01</p> <p>Atomistic simulation methods have been used to calculate and compare the surface structures and energies of the {l_brace}10{bar 1}4{r_brace}, {l_brace}0001{r_brace}, {l_brace}10{bar 1}0{r_brace}, {l_brace}11{bar 2}0{r_brace} and {l_brace}10{bar 1}1{r_brace} surfaces of <span class="hlt">calcite</span> and dolomite and to evaluate their equilibrium morphologies. The <span class="hlt">calcite</span> {l_brace}10{bar 1}4{r_brace} and the dolomite {l_brace}10{bar 1}0{r_brace} and {l_brace}11{bar 2}0{r_brace} surfaces are the most stable <span class="hlt">crystal</span> planes. Investigation of the segregation of Mg and Ca ions in the dolomite <span class="hlt">crystal</span> shows a clear preference for Ca{sup 2+} ions at the surface sites and for Mg{sup 2+} ions in the bulk sites and hence growth onto dolomite results in calcium carbonate or high magnesian <span class="hlt">calcite</span> <span class="hlt">crystals</span> which helps explain the difficulty in <span class="hlt">crystallizing</span> dolomite vs. <span class="hlt">calcite</span> under laboratory conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/2254924','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/2254924"><span><span class="hlt">Crystallization</span> and preliminary X-ray studies of psophocarpin B1, a chymotrypsin inhibitor from winged bean <span class="hlt">seeds</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Dattagupta, J K; Chakrabarti, C; Podder, A; Dutta, S K; Singh, M</p> <p>1990-11-20</p> <p>Psophocarpin B1 is a 20,000 Mr protein of winged bean (Psophocarpus tetragonolobus) <span class="hlt">seeds</span> having chymotrypsin inhibitory activity. Single <span class="hlt">crystals</span> of this protein suitable for X-ray crystallographic studies have been obtained by the vapour diffusion method using ammonium sulphate. The <span class="hlt">crystals</span> are hexagonal, space group P6(4)22 or P6(2)22, cell dimensions a = b = 61 A, c = 210 A. They are stable to irradiation with X-rays and diffract to at least 2.6 A resolution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22378001','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22378001"><span>An approach for phosphate removal with quartz sand, ceramsite, blast furnace slag and steel slag as <span class="hlt">seed</span> <span class="hlt">crystal</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Qiu, Liping; Wang, Guangwei; Zhang, Shoubin; Yang, Zhongxi; Li, Yanbo</p> <p>2012-01-01</p> <p>The phosphate removal abilities and <span class="hlt">crystallization</span> performance of quartz sand, ceramsite, blast furnace slag and steel slag were investigated. The residual phosphate concentrations in the reaction solutions were not changed by addition of the ceramsite, quartz sand and blast furnace slag. The steel slag could provide alkalinity and Ca(2+) to the reaction solution due to its hydration activity, and performed a better phosphate removal performance than the other three. Under the conditions of Ca/P 2.0, pH 8.5 and 10 mg P/L, the phosphate <span class="hlt">crystallization</span> occurred during 12 h. The quartz sand and ceramsite did not improve the phosphate <span class="hlt">crystallization</span>, but steel slag was an effective <span class="hlt">seed</span> <span class="hlt">crystal</span>. The phosphate concentration decreased drastically after 12 h after addition of steel slag, and near complete removal was achieved after 48 h. The XRD analysis showed that the main <span class="hlt">crystallization</span> products were hydroxyapatite (HAP) and the crystallinity increased with the reaction time. Phosphate was successfully recovered from low phosphate concentration wastewater using steel slag as <span class="hlt">seed</span> material.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999JCrGr.196..356Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999JCrGr.196..356Z"><span>Human 17β-hydroxysteroid dehydrogenase-ligand complexes: <span class="hlt">crystals</span> of different space groups with various cations and combined <span class="hlt">seeding</span> and co-<span class="hlt">crystallization</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhu, D.-W.; Han, Q.; Qiu, W.; Campbell, R. L.; Xie, B.-X.; Azzi, A.; Lin, S.-X.</p> <p>1999-01-01</p> <p>Human estrogenic 17β-hydroxysteroid dehydrogenase (17β-HSD1) is responsible for the synthesis of active estrogens that stimulate the proliferation of breast cancer cells. The enzyme has been <span class="hlt">crystallized</span> using a Mg 2+/PEG (3500)/β-octyl glucoside system [Zhu et al., J. Mol. Biol. 234 (1993) 242]. The space group of these <span class="hlt">crystals</span> is C2. Here we report that cations can affect 17β-HSD1 <span class="hlt">crystallization</span> significantly. In the presence of Mn 2+ instead of Mg 2+, <span class="hlt">crystals</span> have been obtained in the same space group with similar unit cell dimensions. In the presence of Li + and Na + instead of Mg 2+, the space group has been changed to P2 12 12 1. A whole data set for a <span class="hlt">crystal</span> of 17ß-HSD1 complex with progesterone grown in the presence of Li + has been collected to 1.95 Å resolution with a synchrotron source. The cell dimensions are a=41.91 Å, b=108.21 Å, c=117.00 Å. The structure has been preliminarily determined by molecular replacement, yielding important information on <span class="hlt">crystal</span> packing in the presence of different cations. In order to further understand the structure-function relationship of 17β-HSD1, enzyme complexes with several ligands have been <span class="hlt">crystallized</span>. As the steroids have very low aqueous solubility, we used a combined method of <span class="hlt">seeding</span> and co-<span class="hlt">crystallization</span> to obtain <span class="hlt">crystals</span> of 17β-HSD1 complexed with various ligands. This method provides ideal conditions for growing complex <span class="hlt">crystals</span>, with ligands such as 20α-hydroxysteroid progesterone, testosterone and 17β-methyl-estradiol-NADP +. Several complex structures have been determined with reliable electronic density of the bound ligands.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_7 --> <div id="page_8" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="141"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JVGR..323...38M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JVGR..323...38M"><span><span class="hlt">Calcite</span> sealing in a fractured geothermal reservoir: Insights from combined EBSD and chemistry mapping</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McNamara, David D.; Lister, Aaron; Prior, Dave J.</p> <p>2016-09-01</p> <p>Fractures play an important role as fluid flow pathways in geothermal resources hosted in indurated greywacke basement of the Taupo Volcanic Zone, New Zealand, including the Kawerau Geothermal Field. Over time, the permeability of such geothermal reservoirs can be degraded by fracture sealing as minerals deposit out of transported geothermal fluids. <span class="hlt">Calcite</span> is one such fracture sealing mineral. This study, for the first time, utilises combined data from electron backscatter diffraction and chemical mapping to characterise <span class="hlt">calcite</span> vein fill morphologies, and gain insight into the mechanisms of <span class="hlt">calcite</span> fracture sealing in the Kawerau Geothermal Field. Two <span class="hlt">calcite</span> sealing mechanisms are identified 1) asymmetrical syntaxial growth of <span class="hlt">calcite</span>, inferred by the presence of single, twinned, <span class="hlt">calcite</span> <span class="hlt">crystals</span> spanning the entire fracture width, and 2) 3D, interlocking growth of bladed vein <span class="hlt">calcite</span> into free space as determined from chemical and crystallographic orientation mapping. This study also identifies other potential uses of combined EBSD and chemical mapping to understand geothermal field evolution including, potentially informing on levels of fluid supersaturation from the study of <span class="hlt">calcite</span> lattice distortion, and providing information on a reservoir's history of stress, strain, and deformation through investigation of <span class="hlt">calcite</span> <span class="hlt">crystal</span> deformation and twinning patterns.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2225371','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2225371"><span>Combining site-specific mutagenesis and <span class="hlt">seeding</span> as a strategy to <span class="hlt">crystallize</span> ‘difficult’ proteins: the case of Staphylococcus aureus thioredoxin</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Roos, Goedele; Brosens, Elke; Wahni, Khadija; Desmyter, Aline; Spinelli, Silvia; Wyns, Lode; Messens, Joris; Loris, Remy</p> <p>2006-01-01</p> <p>The P31T mutant of Staphylococcus aureus thioredoxin <span class="hlt">crystallizes</span> spontaneously in space group P212121, with unit-cell parameters a = 41.7, b = 49.5, c = 55.6 Å. The <span class="hlt">crystals</span> diffract to 2.2 Å resolution. Isomorphous <span class="hlt">crystals</span> of wild-type thioredoxin as well as of other point mutants only grow when <span class="hlt">seeded</span> with the P31T mutant. These results suggest <span class="hlt">seeding</span> as a valuable tool complementing surface engineering for proteins that are hard to <span class="hlt">crystallize</span>. PMID:17142910</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3946587','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3946587"><span>Biotic Control of Skeletal Growth by Scleractinian Corals in Aragonite–<span class="hlt">Calcite</span> Seas</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Higuchi, Tomihiko; Fujimura, Hiroyuki; Yuyama, Ikuko; Harii, Saki; Agostini, Sylvain; Oomori, Tamotsu</p> <p>2014-01-01</p> <p>Modern scleractinian coral skeletons are commonly composed of aragonite, the orthorhombic form of CaCO3. Under certain conditions, modern corals produce <span class="hlt">calcite</span> as a secondary precipitate to fill pore space. However, coral construction of primary skeletons from <span class="hlt">calcite</span> has yet to be demonstrated. We report a <span class="hlt">calcitic</span> primary skeleton produced by the modern scleractinian coral Acropora tenuis. When uncalcified juveniles were incubated from the larval stage in seawater with low mMg/Ca levels, the juveniles constructed <span class="hlt">calcitic</span> <span class="hlt">crystals</span> in parts of the primary skeleton such as the septa; the deposits were observable under Raman microscopy. Using scanning electron microscopy, we observed different <span class="hlt">crystal</span> morphologies of aragonite and <span class="hlt">calcite</span> in a single juvenile skeleton. Quantitative analysis using X-ray diffraction showed that the majority of the skeleton was composed of aragonite even though we had exposed the juveniles to manipulated seawater before their initial <span class="hlt">crystal</span> nucleation and growth processes. Our results indicate that the modern scleractinian coral Acropora mainly produces aragonite skeletons in both aragonite and <span class="hlt">calcite</span> seas, but also has the ability to use <span class="hlt">calcite</span> for part of its skeletal growth when incubated in <span class="hlt">calcite</span> seas. PMID:24609012</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996JCrGr.167..638M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996JCrGr.167..638M"><span>Top-<span class="hlt">seeded</span> solution growth of Bi 12TiO 20 single <span class="hlt">crystals</span> doped with P</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miyazawa, Shintaro</p> <p>1996-10-01</p> <p>P-doped, [001]-oriented sillenite Bi 12TiO 20 single <span class="hlt">crystals</span> are grown by top-<span class="hlt">seeded</span> solution growth from BiPO 4-Bi 2O 3-Bi 12TiO 20 solutions with a newly developed double-crucible configuration. P-doping resulted in clear <span class="hlt">crystal</span> habit/facet modifications in the growth modes of Bi 12TiO 20 in which [lcub]100[rcub] facets became predominant. Chemical analysis of the <span class="hlt">crystals</span> showed that P substitutes Ti sites, allowing Bi 12(Ti 1 - xP x)O 20 solid-solution, but the solubility of P seemed to limit up to 75% of Ti. P-doping resulted in a bleaching of the optical absorption shoulder and blue-shift of the absorption edge, and also in an increase of an optical rotatory power reached about 14°/mm from 6°/mm of undoped one.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APExp..10a1003I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APExp..10a1003I"><span>Highly resistive C-doped hydride vapor phase epitaxy-GaN grown on ammonothermally <span class="hlt">crystallized</span> GaN <span class="hlt">seeds</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Iwinska, Malgorzata; Piotrzkowski, Ryszard; Litwin-Staszewska, Elzbieta; Sochacki, Tomasz; Amilusik, Mikolaj; Fijalkowski, Michal; Lucznik, Boleslaw; Bockowski, Michal</p> <p>2017-01-01</p> <p>GaN <span class="hlt">crystals</span> were grown by hydride vapor phase epitaxy (HVPE) and doped with C. The <span class="hlt">seeds</span> were high-structural-quality ammonothermally <span class="hlt">crystallized</span> GaN. The grown <span class="hlt">crystals</span> were highly resistive at 296 K and of high structural quality. High-temperature Hall effect measurements revealed p-type conductivity and a deep acceptor level in the material with an activation energy of 1 eV. This is in good agreement with density functional theory calculations based on hybrid functionals as presented by the Van de Walle group. They obtained an ionization energy of 0.9 eV when C was substituted for N in GaN and acted as a deep acceptor.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70017028','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70017028"><span>Time and metamorphic petrology: <span class="hlt">Calcite</span> to aragonite experiments</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hacker, B.R.; Kirby, S.H.; Bohlen, S.R.</p> <p>1992-01-01</p> <p>Although the equilibrium phase relations of many mineral systems are generally well established, the rates of transformations, particularly in polycrystalline rocks, are not. The results of experiments on the <span class="hlt">calcite</span> to aragonite transformation in polycrystalline marble are different from those for earlier experiments on powdered and single-<span class="hlt">crystal</span> <span class="hlt">calcite</span>. The transformation in the polycrystalline samples occurs by different mechanisms, with a different temperature dependence, and at a markedly slower rate. This work demonstrates the importance of kinetic studies on fully dense polycrystalline aggregates for understanding mineralogic phase changes in nature. Extrapolation of these results to geological time scales suggests that transformation of <span class="hlt">calcite</span> to aragonite does not occur in the absence of volatiles at temperatures below 200??C. Kinetic hindrance is likely to extend to higher temperatures in more complex transformations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3483407','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3483407"><span>Sea urchin tooth mineralization: <span class="hlt">Calcite</span> present early in the aboral plumula</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Stock, Stuart R.; Veis, Arthur; Xiao, Xianghui; Almer, Jonathan D.; Dorvee, Jason R.</p> <p>2012-01-01</p> <p>In both vertebrate bone, containing carbonated hydroxyapatite as the mineral phase, and in invertebrate hard tissue comprised of calcium carbonate, a popular view is that the mineral phase develops from a long-lived amorphous precursor which later transforms into <span class="hlt">crystal</span> form. Important questions linked to this popular view are: When and where is the <span class="hlt">crystallized</span> material formed, and is amorphous solid added subsequently to the crystalline substrate? Sea urchin teeth, in which the earliest mineral forms within isolated compartments, in a time and position dependent manner, allow direct investigation of the timing of <span class="hlt">crystallization</span> of the <span class="hlt">calcite</span> primary plates. Living teeth of the sea urchin Lytechinus variegatus, in their native coelomic fluid, were examined by high-energy synchrotron x-ray diffraction. The diffraction data show that <span class="hlt">calcite</span> is present in the most aboral portions of the plumula, representing the very earliest stages of mineralization, and that this <span class="hlt">calcite</span> has the same <span class="hlt">crystal</span> orientation as in the more mature adoral portions of the same tooth. Raman spectroscopy of the aboral plumula confirms the initial primary plate mineral material is <span class="hlt">calcite</span> and does not detect amorphous calcium carbonate; in the more mature adoral incisal flange, it does detect a broader <span class="hlt">calcite</span> peak, consistent with two or more magnesium compositions. We hypothesize that some portion of each syncytial membrane in the plumula provides the information for nucleation of identically oriented <span class="hlt">calcite</span> <span class="hlt">crystals</span> that subsequently develop to form the complex geometry of the single <span class="hlt">crystal</span> sea urchin tooth. PMID:22940703</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatMa..15..903K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatMa..15..903K"><span>Tuning hardness in <span class="hlt">calcite</span> by incorporation of amino acids</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kim, Yi-Yeoun; Carloni, Joseph D.; Demarchi, Beatrice; Sparks, David; Reid, David G.; Kunitake, Miki E.; Tang, Chiu C.; Duer, Melinda J.; Freeman, Colin L.; Pokroy, Boaz; Penkman, Kirsty; Harding, John H.; Estroff, Lara A.; Baker, Shefford P.; Meldrum, Fiona C.</p> <p>2016-08-01</p> <p>Structural biominerals are inorganic/organic composites that exhibit remarkable mechanical properties. However, the structure-property relationships of even the simplest building unit--mineral single <span class="hlt">crystals</span> containing embedded macromolecules--remain poorly understood. Here, by means of a model biomineral made from <span class="hlt">calcite</span> single <span class="hlt">crystals</span> containing glycine (0-7 mol%) or aspartic acid (0-4 mol%), we elucidate the origin of the superior hardness of biogenic <span class="hlt">calcite</span>. We analysed lattice distortions in these model <span class="hlt">crystals</span> by using X-ray diffraction and molecular dynamics simulations, and by means of solid-state nuclear magnetic resonance show that the amino acids are incorporated as individual molecules. We also demonstrate that nanoindentation hardness increased with amino acid content, reaching values equivalent to their biogenic counterparts. A dislocation pinning model reveals that the enhanced hardness is determined by the force required to cut covalent bonds in the molecules.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010GeCoA..74.6751H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010GeCoA..74.6751H"><span>Application of <span class="hlt">calcite</span> Mg partitioning functions to the reconstruction of paleocean Mg/Ca</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hasiuk, Franciszek J.; Lohmann, Kyger C.</p> <p>2010-12-01</p> <p><span class="hlt">Calcite</span> Mg/Ca is usually assumed to vary linearly with solution Mg/Ca, that a constant partition coefficient describes the relationship between these two ratios. Numerous published empirical datasets suggests that this relationship is better described by a power function. We provide a compilation of these literature data for biotic and abiotic <span class="hlt">calcite</span> in the form of <span class="hlt">Calcite</span> Mg/Ca = F(Solution Mg/Ca) H, where F and H are empirically determined fitting parameters describing the slope and deviation from linearity, respectively, of the function. This is equivalent to Freundlich sorption behavior controlling Mg incorporation in <span class="hlt">calcite</span>. Using a power function, instead of a partition coefficient, lowers Phanerozoic seawater Mg/Ca estimates based on echinoderm skeletal material by, on average, 0.5 mol/mol from previous estimates. These functions can also be used to model the primary skeletal <span class="hlt">calcite</span> Mg/Ca of numerous <span class="hlt">calcite</span> phases through geologic time. Such modeling suggests that the Mg/Ca of all <span class="hlt">calcite</span> precipitated from seawater has varied through the Phanerozoic in response to changing seawater Mg/Ca and that the overall range in Mg/Ca measured among various <span class="hlt">calcite</span> phases would be greatest when seawater Mg/Ca was also high (e.g., "aragonite seas") and lowest when seawater Mg/Ca was low (e.g., "<span class="hlt">calcite</span> seas"). It follows that, during times of "<span class="hlt">calcite</span> seas" when the seawater Mg/Ca is presumed to have been lower, deposition of <span class="hlt">calcite</span> with low Mg contents would have resulted in a depressed drive for diagenetic stabilization of shelfal carbonate and, in turn, lead to greater preservation of <span class="hlt">crystal</span> and skeletal microfabrics and primary chemistries in biotic and abiotic <span class="hlt">calcites</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011APS..MARD39015E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011APS..MARD39015E"><span>Enhancing mechanical properties of <span class="hlt">calcite</span> by Mg substitutions: An ab initio study</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Elstnerova, Pavlina; Friak, Martin; Hickel, Tilmann; Fabritius, Helge Otto; Lymperakis, Liverios; Petrov, Michal; Raabe, Dierk; Neugebauer, Joerg; Nikolov, Svetoslav; Zigler, Andreas; Hild, Sabine</p> <p>2011-03-01</p> <p>Arthropoda representing a majority of all known animal species are protected by an exoskeleton formed by their cuticle. The cuticle represents a hierarchically structured multifunctional bio-composite based on chitin and proteins. Some groups like Crustacea reinforce the load-bearing parts of their cuticle with <span class="hlt">calcite</span>. As the <span class="hlt">calcite</span> sometimes contains Mg it was speculated that Mg may have a stiffening impact on the mechanical properties of the cuticle. We present a theoretical parameter-free quantum-mechanical study of thermodynamic, structural and elastic properties of Mg-substituted <span class="hlt">calcite</span>. Our results show that substituting Ca by Mg causes an almost linear decrease in the <span class="hlt">crystal</span> volume with Mg concentration and of substituted <span class="hlt">crystals</span>. As a consequence the <span class="hlt">calcite</span> <span class="hlt">crystals</span> become stiffer giving rise e.g. to substantially increased bulk moduli.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21768106','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21768106"><span><span class="hlt">Calcite</span> formation in soft coral sclerites is determined by a single reactive extracellular protein.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rahman, M Azizur; Oomori, Tamotsu; Wörheide, Gert</p> <p>2011-09-09</p> <p>Calcium carbonate exists in two main forms, <span class="hlt">calcite</span> and aragonite, in the skeletons of marine organisms. The primary mineralogy of marine carbonates has changed over the history of the earth depending on the magnesium/calcium ratio in seawater during the periods of the so-called "<span class="hlt">calcite</span> and aragonite seas." Organisms that prefer certain mineralogy appear to flourish when their preferred mineralogy is favored by seawater chemistry. However, this rule is not without exceptions. For example, some octocorals produce <span class="hlt">calcite</span> despite living in an aragonite sea. Here, we address the unresolved question of how organisms such as soft corals are able to form <span class="hlt">calcitic</span> skeletal elements in an aragonite sea. We show that an extracellular protein called ECMP-67 isolated from soft coral sclerites induces <span class="hlt">calcite</span> formation in vitro even when the composition of the calcifying solution favors aragonite precipitation. Structural details of both the surface and the interior of single <span class="hlt">crystals</span> generated upon interaction with ECMP-67 were analyzed with an apertureless-type near-field IR microscope with high spatial resolution. The results show that this protein is the main determining factor for driving the production of <span class="hlt">calcite</span> instead of aragonite in the biocalcification process and that -OH, secondary structures (e.g. α-helices and amides), and other necessary chemical groups are distributed over the center of the <span class="hlt">calcite</span> <span class="hlt">crystals</span>. Using an atomic force microscope, we also explored how this extracellular protein significantly affects the molecular-scale kinetics of <span class="hlt">crystal</span> formation. We anticipate that a more thorough investigation of the proteinaceous skeleton content of different <span class="hlt">calcite</span>-producing marine organisms will reveal similar components that determine the mineralogy of the organisms. These findings have significant implications for future models of the <span class="hlt">crystal</span> structure of <span class="hlt">calcite</span> in nature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3173117','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3173117"><span><span class="hlt">Calcite</span> Formation in Soft Coral Sclerites Is Determined by a Single Reactive Extracellular Protein*</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Rahman, M. Azizur; Oomori, Tamotsu; Wörheide, Gert</p> <p>2011-01-01</p> <p>Calcium carbonate exists in two main forms, <span class="hlt">calcite</span> and aragonite, in the skeletons of marine organisms. The primary mineralogy of marine carbonates has changed over the history of the earth depending on the magnesium/calcium ratio in seawater during the periods of the so-called “<span class="hlt">calcite</span> and aragonite seas.” Organisms that prefer certain mineralogy appear to flourish when their preferred mineralogy is favored by seawater chemistry. However, this rule is not without exceptions. For example, some octocorals produce <span class="hlt">calcite</span> despite living in an aragonite sea. Here, we address the unresolved question of how organisms such as soft corals are able to form <span class="hlt">calcitic</span> skeletal elements in an aragonite sea. We show that an extracellular protein called ECMP-67 isolated from soft coral sclerites induces <span class="hlt">calcite</span> formation in vitro even when the composition of the calcifying solution favors aragonite precipitation. Structural details of both the surface and the interior of single <span class="hlt">crystals</span> generated upon interaction with ECMP-67 were analyzed with an apertureless-type near-field IR microscope with high spatial resolution. The results show that this protein is the main determining factor for driving the production of <span class="hlt">calcite</span> instead of aragonite in the biocalcification process and that –OH, secondary structures (e.g. α-helices and amides), and other necessary chemical groups are distributed over the center of the <span class="hlt">calcite</span> <span class="hlt">crystals</span>. Using an atomic force microscope, we also explored how this extracellular protein significantly affects the molecular-scale kinetics of <span class="hlt">crystal</span> formation. We anticipate that a more thorough investigation of the proteinaceous skeleton content of different <span class="hlt">calcite</span>-producing marine organisms will reveal similar components that determine the mineralogy of the organisms. These findings have significant implications for future models of the <span class="hlt">crystal</span> structure of <span class="hlt">calcite</span> in nature. PMID:21768106</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA452565','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA452565"><span>Corrosion Protection by <span class="hlt">Calcite</span>-Type Coatings</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1989-10-01</p> <p>CORROSION PROTECTION BY <span class="hlt">CALCITE</span> -TYPE COATINGS OCTOBER, 1989 Prepared by: OCEAN CITY RESEARCH CORPORATION Tennessee Avenue & Beach Thorofare Ocean...REPORT DATE OCT 1989 2. REPORT TYPE N/A 3. DATES COVERED - 4. TITLE AND SUBTITLE Corrosion Protection by <span class="hlt">Calcite</span> -Type Coatings 5a. CONTRACT... <span class="hlt">calcite</span> -type coatings to segregated seawater ballast tanks. If perfected, a <span class="hlt">calcite</span> coating approach could substantially reduce the cost of corrosion</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2705649','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2705649"><span>Purification, <span class="hlt">crystallization</span> and preliminary crystallographic studies of a Kunitz-type proteinase inhibitor from tamarind (Tamarindus indica) <span class="hlt">seeds</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Patil, Dipak N.; Preeti; Chaudhry, Anshul; Sharma, Ashwani K.; Tomar, ­Shailly; Kumar, Pravindra</p> <p>2009-01-01</p> <p>A Kunitz-type proteinase inhibitor has been purified from tamarind (Tamarindus indica) <span class="hlt">seeds</span>. SDS–PAGE analysis of a purified sample showed a homogeneous band corresponding to a molecular weight of 21 kDa. The protein was identified as a Kunitz-type proteinase inhibitor based on N-terminal amino-acid sequence analysis. It was <span class="hlt">crystallized</span> by the vapour-diffusion method using PEG 6000. The <span class="hlt">crystals</span> belonged to the orthorhombic space group C2221, with unit-cell parameters a = 37.2, b = 77.1, c = 129.1 Å. Diffraction data were collected to a resolution of 2.7 Å. Preliminary crystallographic analysis indicated the presence of one proteinase inhibitor molecule in the asymmetric unit, with a solvent content of 44%. PMID:19574654</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998SedG..116...13H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998SedG..116...13H"><span>Low limit of Mn 2+-activated cathodoluminescence of <span class="hlt">calcite</span>: state of the art</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Habermann, Dirk; Neuser, Rolf D.; Richter, Detlev K.</p> <p>1998-02-01</p> <p>In the literature, the lower limit for Mn 2+-activated cathodoluminescence (CL) of <span class="hlt">calcite</span> is variously reputed to over a very wide range of values above 10 ppm Mn. Our spectroscopic investigations of the CL response in natural <span class="hlt">calcite</span> reveal that below 10 ppm manganese content Mn 2+-activation is also present. Using the Quantitative High Resolution Spectral analysis of CL (QHRS-CL) an activation by Mn 2+ in the range of 700 ppb is proved, which cannot be determined visually. So, if not quenched, the minimum Mn 2+ content for Mn 2+-activation is one atom in the irradiated <span class="hlt">calcite</span> <span class="hlt">crystal</span> lattice volume. As the intrinsic (background blue) luminescence is used to determine non-altered biogenic <span class="hlt">calcite</span>, the limit of Mn 2+-activation plays an important role in the interpretation of diagenetic processes. Our results of spectroscopic analyses require a revision of current opinions about the diagenesis of <span class="hlt">calcite</span> as revealed by CL investigation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25063580','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25063580"><span>Aragonite shells are more ancient than <span class="hlt">calcite</span> ones in bivalves: new evidence based on omics.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wang, Xiaotong; Li, Li; Zhu, Yabing; Song, Xiaorui; Fang, Xiaodong; Huang, Ronglian; Que, Huayong; Zhang, Guofan</p> <p>2014-11-01</p> <p>Two calcium carbonate <span class="hlt">crystal</span> polymorphs, aragonite and <span class="hlt">calcite</span>, are the main inorganic components of mollusk shells. Some fossil evidences suggest that aragonite shell is more ancient than <span class="hlt">calcite</span> shell for the Bivalvia. But, the molecular biology evidence for the above deduction is absent. In this study, we searched for homologs of bivalve aragonite-related and <span class="hlt">calcite</span>-related shell proteins in the oyster genome, and found that no homologs of <span class="hlt">calcite</span>-related shell protein but some homologs of aragonite-related shell proteins in the oyster genome. We explained the results as the new evidence to support that aragonite shells are more ancient than <span class="hlt">calcite</span> shells in bivalves combined the published biogeological and seawater chemistry data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/37117','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/37117"><span>Noncrystallographic <span class="hlt">calcite</span> dendrites from hot-spring deposits at Lake Bogoria, Kenya</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Jones, B.; Renaut, R.W.</p> <p>1995-01-02</p> <p>Complex <span class="hlt">calcite</span> <span class="hlt">crystals</span> are an integral component of precipitates that form around the orifices of the Loburu and Mawe Moto hot springs on the shores of Lake bogoria, Kenya. Two types of large (up to 4 cm long) noncrystallographic dendrites are important components of these deposits. Feather dendrites are characterized by multiple levels of branching with individual branches developed through <span class="hlt">crystal</span> splitting and spherulitic growth. Scandulitic (from Latin meaning shingle) dendrites are formed of stacked <span class="hlt">calcite</span> <span class="hlt">crystals</span> and are generally more compact than feather dendrites. These developed through the incremental stacking of rectangular-shaped <span class="hlt">calcite</span> <span class="hlt">crystals</span> that initially grew as skeletal <span class="hlt">crystals</span>. Feather and scandulitic dendrites precipitated from the same waters in the same springs. The difference in morphology is therefore related to microenvironments in which they grew. Feather dendrites grew in any direction in pools of free-standing water provided that they were in constant contact with the solute. Conversely, scandulitic dendrites grew on rims of dams where water flowed over the surface in concert with the pulses of spring water. Thus, each <span class="hlt">calcite</span> <span class="hlt">crystal</span> in these dendrites represents one episode of <span class="hlt">crystal</span> growth. The orientation of the component <span class="hlt">crystals</span> in scandulitic dendrites is controlled by the topography of the dam or surface, not crystallographic criteria. The noncrystallographic dendrites formed from spring waters with initial temperatures of 90--99 C. Surficial water cooling, loss of CO{sub 2}, and presence of other elements that can interfere with <span class="hlt">crystal</span> growth contributed to the formation of these unusual <span class="hlt">crystals</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22356158','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22356158"><span><span class="hlt">Crystallization</span> and preliminary X-ray diffraction analysis of a new chitin-binding protein from Parkia platycephala <span class="hlt">seeds</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Cavada, Benildo S. Castellón, Rolando E. R.; Vasconcelos, Georg G.; Rocha, Bruno A. M.; Bezerra, Gustavo A.; Debray, Henri; Delatorre, Plínio; Nagano, Celso S.; Toyama, Marcos; Pinto, Vicente P. T.; Moreno, Frederico B. M. B.; Canduri, Fernanda; Azevedo, Walter F. Jr de</p> <p>2005-09-01</p> <p><span class="hlt">Crystals</span> of P. platycephala chintinase/lectin (PPL-2) belong to the orthorhombic space group P2{sub 1}2{sub 1}2{sub 1}, with unit-cell parameters a = 55.19, b = 59.95, c = 76.60 Å. The preliminary cystal structure of PPL-2 was solved at a resolution of 1.73 Å by molecular replacement, presenting a correlation coefficient of 0.558 and an R factor of 0.439. A chitin-binding protein named PPL-2 was purified from Parkia platycephala <span class="hlt">seeds</span> and <span class="hlt">crystallized</span>. <span class="hlt">Crystals</span> belong to the orthorhombic space group P2{sub 1}2{sub 1}2{sub 1}, with unit-cell parameters a = 55.19, b = 59.95, c = 76.60 Å, and grew over several days at 293 K using the hanging-drop method. Using synchrotron radiation, a complete structural data set was collected to 1.73 Å resolution. The preliminary <span class="hlt">crystal</span> structure of PPL-2, determined by molecular replacement, presents a correlation coefficient of 0.558 and an R factor of 0.439. Crystallographic refinement is in progress.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009JAP...105gC311Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009JAP...105gC311Y"><span>Manipulation of the <span class="hlt">crystal</span> structures and the consequent FMR behaviors in GaAs/Ag/Fe system with an ultrathin Fe <span class="hlt">seeding</span> layer</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yu, C. C.; Teng, Y. H.; Tsai, C. S.; Yao, Y. D.; Liou, Y.</p> <p>2009-04-01</p> <p>The <span class="hlt">crystal</span> structures, magnetic properties, and the behaviors of ferromagnetic resonance of the GaAs(001)/Fe/Ag/Fe multilayers with different thicknesses of the Fe <span class="hlt">seeding</span> layer are investigated. For the first time, a transformation from polycrystal into nearly bcc (001) single-<span class="hlt">crystal</span> structure is observed in the top Fe layer while the thickness of the Fe <span class="hlt">seeding</span> layer increases. The frequency of ferromagnetic resonance in Fe/Ag/Fe multilayers can be tuned by varying the strength of the external magnetic field and the thickness of the Fe <span class="hlt">seeding</span> layer. Also it can be well fitted by the resonance equation. The correlation between <span class="hlt">crystal</span> structures and ferromagnetic resonance manifests itself.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996GeCoA..60.4417V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996GeCoA..60.4417V"><span>Paleotransport of lanthanides and strontium recorded in <span class="hlt">calcite</span> compositions from tuffs at Yucca Mountain, Nevada, USA</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vaniman, David T.; Chipera, Steve J.</p> <p>1996-11-01</p> <p>Secondary <span class="hlt">calcite</span> occurs in both saturated and unsaturated hydrologic zones (SZ and UZ, respectively) in the tuffs at Yucca Mountain, Nevada, USA. In the upper UZ, the major constituents of the <span class="hlt">calcite</span> <span class="hlt">crystal</span> structure (C, O) have surface origins. At greater depth there is a “barren zone,” straddling the water table, where <span class="hlt">calcite</span> is rare and mixing of surface and subsurface sources may occur. Deep in the SZ, distinctive Mn <span class="hlt">calcites</span> reflect deep sources, including Ca released as analcime or albite formed and carbonates derived from underlying Paleozoic rocks. In the UZ and in the barren zone, above the deep Mn <span class="hlt">calcites</span>, variations in <span class="hlt">calcite</span> lanthanide chemistry can be used to distinguish rhyolitic from quartz-latitic sources. Lanthanide ratios and Sr contents of <span class="hlt">calcites</span> record the chemical evolution of waters flowing through the UZ and upper SZ. Variations in <span class="hlt">calcite</span> chemistry in the UZ and in the barren zone show that (1) Sr, which is readily exchanged with clays or zeolites, is essentially removed from some flowpaths that are in contact with these minerals and (2) traces of Mn oxides found in the tuffs have a significant effect on groundwater chemistry in the UZ and in the barren zone by removing almost all Ce from solution (evidenced by characteristic Ce depletions in <span class="hlt">calcite</span> throughout this zone). Extreme Ce removal may be a result of Ce oxidation (Ce 3+→ Ce 4+) at the surfaces of some Mn oxides, particularly rancieite. Higher Sr contents and lack of Ce depletions in the deeper Mn <span class="hlt">calcites</span> reflect different ages, origins, and transport systems. The <span class="hlt">calcite</span> record of lanthanide and Sr transport in the UZ shows that minor minerals (clays and zeolites) and even trace minerals (Mn oxides) will affect the compositions of groundwaters that flow over distances greater than a few tens of meters.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_8 --> <div id="page_9" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="161"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012JCrGr.353...12B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012JCrGr.353...12B"><span>Optimizing <span class="hlt">seeded</span> casting of mono-like silicon <span class="hlt">crystals</span> through numerical simulation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Black, Andrés; Medina, Juan; Piñeiro, Axa; Dieguez, Ernesto</p> <p>2012-08-01</p> <p>Recently, silicon ingots produced by typical multicrystalline casting systems but having monocrystalline features are entering the photovoltaic market. In order to look into the particular properties of this novel method, the normal silicon casting process is numerically simulated, and compared to an optimized mono-like casting process, based on the use of oriented monocrystalline silicon <span class="hlt">seeds</span>. The <span class="hlt">seeding</span> process was optimized by reducing the time spent in the melt in order to reduce the back diffusion of harmful non-feedstock metal impurities such as iron, reducing the thermomechanical stress to avoid dislocation multiplication, and decreasing the overall interface curvature. Additionally, the growth conditions in the zone just above the <span class="hlt">seeds</span> were fine-tuned to increase the production of vacancy point defects, in the hope of achieving "vacancy passivation" of harmful interstitial iron by moving it to substitutional position.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/20000842','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/20000842"><span>Fabrication of a good-quality single grain YBCO sample through the control of <span class="hlt">seed</span> <span class="hlt">crystals</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kim, C.J.; Hong, G.W.; Jee, Y.A.; Han, Y.H.; Han, S.C.; Sung, T.H.</p> <p>1999-09-01</p> <p>The authors investigated the growth mode of YBa{sub 2}Cu{sub 3}O{sub 7{minus}y} (Y123) grains and its effect on the levitation forces and trapped magnetic field of top-<span class="hlt">seeded</span> melt processed YBCO samples. When a slab-like Sm-<span class="hlt">seed</span> was used, undesirable subsidiary Y123 grains were formed, while the formation of the subsidiary Y123 grains was suppressed and a nearly single Y123 grain grew when a thick and wide <span class="hlt">seed</span> was used. The formation of the subsidiary Y123 grains decreased the levitation forces and trapped magnetic field, due to the presence of grain boundaries with weak link characteristics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JaJAP..56aAD01H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JaJAP..56aAD01H"><span>Habit control during growth on GaN point <span class="hlt">seed</span> <span class="hlt">crystals</span> by Na-flux method</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Honjo, Masatomo; Imanishi, Masayuki; Imabayashi, Hiroki; Nakamura, Kosuke; Murakami, Kosuke; Matsuo, Daisuke; Maruyama, Mihoko; Imade, Mamoru; Yoshimura, Masashi; Mori, Yusuke</p> <p>2017-01-01</p> <p>The formation of the pyramidal habit is one of the requirements for the dramatic reduction of dislocations during growth on a tiny GaN <span class="hlt">seed</span> called a “point seed”. In this study, we focus on controlling the growth habit to form a pyramidal shape in order to reduce the number of dislocations in the c-growth sector during growth on GaN point <span class="hlt">seeds</span>. High temperature growth was found to change the growth habit from the truncated pyramidal shape to the pyramidal shape. As a result, the number of dislocations in the c-growth sector tended to decrease with increasing growth temperature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24462085','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24462085"><span>Barium recovery by <span class="hlt">crystallization</span> in a fluidized-bed reactor: effects of pH, Ba/P molar ratio and <span class="hlt">seed</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Su, Chia-Chi; Reano, Resmond L; Dalida, Maria Lourdes P; Lu, Ming-Chun</p> <p>2014-06-01</p> <p>The effects of process conditions, including upward velocity inside the column, the amount of added <span class="hlt">seed</span> and <span class="hlt">seed</span> size, the pH value of the precipitant or the phosphate stream and the Ba/P molar ratio in a fluidized-bed reactor (FBR) were studied with a view to producing BaHPO₄ <span class="hlt">crystals</span> of significant size and maximize the removal of barium. XRD were used to identify the products that were collected from the FBR. Experimental results show that an upward velocity of 48 cmmin(-1) produced the largest BaHPO₄ <span class="hlt">crystals</span> with a size of around 0.84-1.0mm. The addition of <span class="hlt">seed</span> <span class="hlt">crystals</span> has no effect on barium removal. The use of a <span class="hlt">seed</span> of a size in the ranges unseeded<0.149-0.29 mm<0.149 mm<0.29-0.42 mm produced increasing amounts of increasingly large <span class="hlt">crystals</span>. The largest BaHPO₄ <span class="hlt">crystals</span> were obtained at pH 8.4-8.8 with a Ba/P molar ratio of 1.0. In the homogeneous and heterogeneous processes, around 98% of barium was removed at pH 8.4-8.6 and [Ba]/[P]=1.0. The XRD results show that a significant amount of barium phosphate (Ba₃(PO₄)₂) was obtained at pH 11. The compounds BaHPO₄ and BaO were present at a pH of below 10.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015ApPhL.107z2106M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015ApPhL.107z2106M"><span>Low-temperature (˜180 °C) position-controlled lateral solid-phase <span class="hlt">crystallization</span> of GeSn with laser-anneal <span class="hlt">seeding</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Matsumura, Ryo; Chikita, Hironori; Kai, Yuki; Sadoh, Taizoh; Ikenoue, Hiroshi; Miyao, Masanobu</p> <p>2015-12-01</p> <p>To realize next-generation flexible thin-film devices, solid-phase <span class="hlt">crystallization</span> (SPC) of amorphous germanium tin (GeSn) films on insulating substrates combined with <span class="hlt">seeds</span> formed by laser annealing (LA) has been investigated. This technique enables the <span class="hlt">crystallization</span> of GeSn at controlled positions at low temperature (˜180 °C) due to the determination of the starting points of <span class="hlt">crystallization</span> by LA <span class="hlt">seeding</span> and Sn-induced SPC enhancement. The GeSn <span class="hlt">crystals</span> grown by SPC from LA <span class="hlt">seeds</span> showed abnormal lateral profiles of substitutional Sn concentration. These lateral profiles are caused by the annealing time after <span class="hlt">crystallization</span> being a function of distance from the LA <span class="hlt">seeds</span>. This observation of a post-annealing effect also indicates that GeSn with a substitutional Sn concentration of up to ˜10% possesses high thermal stability. These results will facilitate the fabrication of next-generation thin-film devices on flexible plastic substrates with low softening temperatures (˜250 °C).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27618958','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27618958"><span>Incorporation of Eu(III) into <span class="hlt">Calcite</span> under Recrystallization conditions.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hellebrandt, S E; Hofmann, S; Jordan, N; Barkleit, A; Schmidt, M</p> <p>2016-09-13</p> <p>The interaction of <span class="hlt">calcite</span> with trivalent europium under recrystallization conditions was studied on the molecular level using site-selective time-resolved laser fluorescence spectroscopy (TRLFS). We conducted batch studies with a reaction time from seven days up to three years with three <span class="hlt">calcite</span> powders, which differed in their specific surface area, recrystallization rates and impurities content. With increase of the recrystallization rate incorporation of Eu(3+) occurs faster and its speciation comes to be dominated by one species with its excitation maximum at 578.8 nm, so far not identified during previous investigations of this process under growth and phase transformation conditions. A long lifetime of 3750 μs demonstrates complete loss of hydration, consequently Eu must have been incorporated into the bulk <span class="hlt">crystal</span>. The results show a strong dependence of the incorporation kinetics on the recrystallization rate of the different <span class="hlt">calcites</span>. Furthermore the investigation of the effect of different background electrolytes (NaCl and KCl) demonstrate that the incorporation process under recrystallization conditions strongly depends on the availability of Na(+). These findings emphasize the different retention potential of <span class="hlt">calcite</span> as a primary and secondary mineral e.g. in a nuclear waste disposal site.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5020613','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5020613"><span>Incorporation of Eu(III) into <span class="hlt">Calcite</span> under Recrystallization conditions</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Hellebrandt, S. E.; Hofmann, S.; Jordan, N.; Barkleit, A.; Schmidt, M.</p> <p>2016-01-01</p> <p>The interaction of <span class="hlt">calcite</span> with trivalent europium under recrystallization conditions was studied on the molecular level using site-selective time-resolved laser fluorescence spectroscopy (TRLFS). We conducted batch studies with a reaction time from seven days up to three years with three <span class="hlt">calcite</span> powders, which differed in their specific surface area, recrystallization rates and impurities content. With increase of the recrystallization rate incorporation of Eu3+ occurs faster and its speciation comes to be dominated by one species with its excitation maximum at 578.8 nm, so far not identified during previous investigations of this process under growth and phase transformation conditions. A long lifetime of 3750 μs demonstrates complete loss of hydration, consequently Eu must have been incorporated into the bulk <span class="hlt">crystal</span>. The results show a strong dependence of the incorporation kinetics on the recrystallization rate of the different <span class="hlt">calcites</span>. Furthermore the investigation of the effect of different background electrolytes (NaCl and KCl) demonstrate that the incorporation process under recrystallization conditions strongly depends on the availability of Na+. These findings emphasize the different retention potential of <span class="hlt">calcite</span> as a primary and secondary mineral e.g. in a nuclear waste disposal site. PMID:27618958</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatSR...633137H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatSR...633137H"><span>Incorporation of Eu(III) into <span class="hlt">Calcite</span> under Recrystallization conditions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hellebrandt, S. E.; Hofmann, S.; Jordan, N.; Barkleit, A.; Schmidt, M.</p> <p>2016-09-01</p> <p>The interaction of <span class="hlt">calcite</span> with trivalent europium under recrystallization conditions was studied on the molecular level using site-selective time-resolved laser fluorescence spectroscopy (TRLFS). We conducted batch studies with a reaction time from seven days up to three years with three <span class="hlt">calcite</span> powders, which differed in their specific surface area, recrystallization rates and impurities content. With increase of the recrystallization rate incorporation of Eu3+ occurs faster and its speciation comes to be dominated by one species with its excitation maximum at 578.8 nm, so far not identified during previous investigations of this process under growth and phase transformation conditions. A long lifetime of 3750 μs demonstrates complete loss of hydration, consequently Eu must have been incorporated into the bulk <span class="hlt">crystal</span>. The results show a strong dependence of the incorporation kinetics on the recrystallization rate of the different <span class="hlt">calcites</span>. Furthermore the investigation of the effect of different background electrolytes (NaCl and KCl) demonstrate that the incorporation process under recrystallization conditions strongly depends on the availability of Na+. These findings emphasize the different retention potential of <span class="hlt">calcite</span> as a primary and secondary mineral e.g. in a nuclear waste disposal site.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22356265','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22356265"><span><span class="hlt">Crystallization</span> and preliminary X-ray diffraction analysis of the lectin from Dioclea rostrata Benth <span class="hlt">seeds</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Delatorre, Plínio; Nascimento, Kyria Santiago; Melo, Luciana Magalhães; Souza, Emmanuel Prata de; Rocha, Bruno Anderson Matias da; Benevides, Raquel G.; Oliveira, Taiana Maia de; Bezerra, Gustavo Arruda; Bezerra, Maria Júlia Barbosa; Cunha, Rodrigo Maranguape Silva da; Cunha, Francisco Assis Bezerra da; Freire, Valder Nogueira; Cavada, Benildo Sousa</p> <p>2006-02-01</p> <p>D. rostrata lectin was <span class="hlt">crystallized</span> by hanging-drop vapor diffusion. The <span class="hlt">crystal</span> belongs to the orthorhombic space group I222 and diffracted to 1.87 Å resolution. Lectins from the Diocleinae subtribe (Leguminosae) are highly similar proteins that promote various biological activities with distinctly differing potencies. The structural basis for this experimental data is not yet fully understood. Dioclea rostrata lectin was purified and <span class="hlt">crystallized</span> by hanging-drop vapour diffusion at 293 K. The <span class="hlt">crystal</span> belongs to the orthorhombic space group I222, with unit-cell parameters a = 61.51, b = 88.22, c = 87.76 Å. Assuming the presence of one monomer per asymmetric unit, the solvent content was estimated to be about 47.9%. A complete data set was collected at 1.87 Å resolution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JCrGr.445...47T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JCrGr.445...47T"><span>Effect of heating conditions on flow patterns during the <span class="hlt">seeding</span> stage of Kyropoulos sapphire <span class="hlt">crystal</span> growth</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Timofeev, Vladimir V.; Kalaev, Vladimir V.; Ivanov, Vadim G.</p> <p>2016-07-01</p> <p>We apply numerical simulation to understand the effect of heating conditions on melt convection in an industrial Ky furnace. The direct numerical simulation (DNS) approach was used to investigate the features of melt flow during the <span class="hlt">seeding</span> stage. Two different cases of Kyropoulos furnace hot zone design were studied numerically, and results were compared with experimental data to understand the effect of modifications on melt convection.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19830034088&hterms=calcite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dcalcite','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19830034088&hterms=calcite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dcalcite"><span>Shock-induced devolatilization of <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Boslough, M. B.; Ahrens, T. J.; Vizgirda, J.; Becker, R. H.; Epstein, S.</p> <p>1982-01-01</p> <p>Experimental measurements of the release adiabats by Vizgirda (1981) indicate that substantial vaporization takes place upon release from shock pressures of 37 GPa for <span class="hlt">calcite</span> and 14 GPa for aragonite. The present investigation includes the first controlled partial vaporization experiments on <span class="hlt">calcite</span>. The experiments were conducted to test the predictions of the release adiabat experiments. The quantities of the gaseous species produced from shocked <span class="hlt">calcite</span> and their carbon and oxygen isotopic compositions were determined, and the shock-induced effect on the Mn(2+) electron spin resonance spectrum in the shock-recovered <span class="hlt">calcite</span> was observed. On the basis of the obtained results, it is concluded that shock stresses at the 17-18 GPa level give rise to volatilization of 0.03-0.3 (mole) percent of <span class="hlt">calcite</span> to CO2 and CO. The devolatilization of <span class="hlt">calcite</span> occurs at low pressure at significantly lower entropy densities than predicted on the basis of thermodynamic continuum models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011JCrGr.325...96Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011JCrGr.325...96Y"><span>Hydrothermal conversion of FAU zeolite into LEV zeolite in the presence of non-calcined <span class="hlt">seed</span> <span class="hlt">crystals</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yashiki, Ayako; Honda, Koutaro; Fujimoto, Ayumi; Shibata, Shohei; Ide, Yusuke; Sadakane, Masahiro; Sano, Tsuneji</p> <p>2011-06-01</p> <p>Hydrothermal conversion of Faujasite-type (FAU) zeolite into Levynite (LEV) zeolite without the use of an organic structure-directing agent (OSDA) was successfully achieved in the presence of non-calcined <span class="hlt">seed</span> <span class="hlt">crystals</span>. The interzeolite conversion depended strongly upon the alkalinity (OH -/SiO 2) of the starting gel, the Si/Al ratio of the starting FAU zeolite and the type of alkaline metal employed. Successful conversion of FAU zeolites into pure LEV zeolite was achieved only for FAU zeolites with Si/Al ratios in the range of 19-26, under highly alkaline conditions (OH -/SiO 2=0.6) by using NaOH as an alkali source. Although the yield of LEV zeolite prepared by this method was lower (18-26%) than that of the conventional hydrothermal synthesis with the use of SDA, the obtained LEV zeolite exhibited a unique core/shell structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999Geo....27..347K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999Geo....27..347K"><span>Alternative origins for nannobacteria-like objects in <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kirkland, Brenda L.; Lynch, F. Leo; Rahnis, Michael A.; Folk, Robert L.; Molineux, Ian J.; McLean, Robert J. C.</p> <p>1999-04-01</p> <p>More than 40 <span class="hlt">calcite</span>-precipitation experiments were performed under sterile conditions in order to investigate the origins of 25 300 nm spherical-, rod-, and ovoid-shaped objects that have been widely interpreted as evidence of nanometer-scale life (i.e., nannobacteria). Individual experiments included the addition of soluble organic compounds, common species of eubacteria, or phage-induced eubacterial lysates. These experiments indicate that many of the nanometer-scale objects have inorganic or nonnannobacterial origins. In the precipitation experiments, <span class="hlt">calcite</span> formed euhedral <span class="hlt">crystals</span> 50 800 nm in diameter and smaller (<50 nm) anhedral or rounded particles or protocrystals. The small anhedral or rounded solids resembled nannobacteria. The relative amount of anhedral or rounded <span class="hlt">calcite</span> was greatest in experiments with a dissolved organic component. These controlled experiments are in accord with observations that rounded nanometer-scale objects are more common in minerals formed in organic-rich environments. Bacterial fragments occur as rounded to irregularly shaped particles that included cell-wall fragments, expulsed cytoplasm, and relict capsules that also closely resembled nannobacteria. Acid etching of the large euhedral <span class="hlt">crystals</span> produced in the precipitation experiments also resulted in the formation of nanometer-scale features that resembled nannobacteria in natural carbonates. The shapes of the etching artifacts vary as a function of the strength of the acid and the duration of etching. Much caution is advisable in interpreting the origin of rounded features <50 nm.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19990108477&hterms=Vapor+pressure&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DVapor%2Bpressure','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19990108477&hterms=Vapor+pressure&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DVapor%2Bpressure"><span>In-Situ Partial Pressure Measurements and Visual Observation during <span class="hlt">Crystal</span> Growth of ZnSe by <span class="hlt">Seeded</span> Physical Vapor Transport</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Su, Ching-Hua; Feth, Shari; Lehoczky, Sandor L.</p> <p>1999-01-01</p> <p>An in-situ monitoring furnace was constructed with side windows to perform partial pressure measurements by optical absorption and visual observation of the growing <span class="hlt">crystal</span>. A fused silica -rowth ampoule with a 4.5 cm long square tube between the source and the <span class="hlt">seed</span> was prepared for the optical absorption measurements. A ZnSe <span class="hlt">crystal</span> was grown by the <span class="hlt">seeded</span> physical vapor transport (PVT) technique in the horizontal configuration. The growth temperature was 1120 C and the furnace translation rate was 3nmVday. Partial pressures of Se2, P(sub Se2), at three locations along the length of the growth ampoule were measured at 90 min intervals during the growth process. The measured P (sub Se2) were in the range of 2.0 to 6.5 x 10(exp -3) atm. The P(sub Se2) results indicated that the partial pressure profile was inconsistent with the results of the one-dimensional diffusion mass transport model and that the source composition shifted toward Se-rich during the run, i.e. the grown <span class="hlt">crystal</span> was more Zn-rich than the source. The visual observation showed that the <span class="hlt">seed</span> <span class="hlt">crystal</span> first etched back, with greater thermal etching occurring along the edges of the <span class="hlt">seed</span> <span class="hlt">crystal</span>. Once the growth started, the <span class="hlt">crystal</span> crew in a predominately contactless mode and facets were evident during growth. The <span class="hlt">crystal</span> did not grow symmetrically which is believed to be due to the unintentional asymmetry of the radial thermal profile in the furnace.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeCoA.183...46P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeCoA.183...46P"><span>NMR spectroscopic study of organic phosphate esters coprecipitated with <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Phillips, Brian L.; Zhang, Zelong; Kubista, Laura; Frisia, Silvia; Borsato, Andrea</p> <p>2016-06-01</p> <p> signals occur with characteristics consistent with phosphate monoesters. The results of this study indicate that trace- to minor concentrations of dissolved organic molecules can be effectively taken up during <span class="hlt">calcite</span> precipitation and incorporated in the structure, leaving a resilient record of materials present during <span class="hlt">crystallization</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20823520','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20823520"><span><span class="hlt">Crystallization</span> and preliminary X-ray studies of a galactose-specific lectin from the <span class="hlt">seeds</span> of bitter gourd (Momordica charantia).</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chandran, Thyageshwar; Sharma, Alok; Vijayan, M</p> <p>2010-09-01</p> <p>A galactose-specific lectin from the <span class="hlt">seeds</span> of bitter gourd (Momordica charantia) is a four-chain type II ribosome-inactivating protein (RIP) resulting from covalent association through a disulfide bridge between two identical copies of a two-chain unit. The available structural information on such four-chain RIPs is meagre. The bitter gourd lectin was therefore <span class="hlt">crystallized</span> for structural investigation and the <span class="hlt">crystals</span> have been characterized. It is anticipated that the structure of the orthorhombic <span class="hlt">crystals</span> will be analysed using molecular replacement by taking advantage of its sequence, and presumably structural, homology to normal two-chain type II RIPs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/journal/1974/vol2issue2/report.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/journal/1974/vol2issue2/report.pdf"><span>Stabilities of <span class="hlt">calcite</span> and aragonite</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Christ, C.L.; Hostetler, P.B.; Siebert, R.M.</p> <p>1974-01-01</p> <p>A revaluation of the 25° C activity-product constants of <span class="hlt">calcite</span> (KC) and aragonite (KA) was made on the basis of the known solubilities of these phases for which the activity of total dissolved calcium was corrected for the presence of the ion pair CaHCO3+ in the aqueous phase. The value of the dissociation constant of CaHCO3+ was taken to be 10-1.225±0.02. This value, combined with values of the analytical concentrations in solutions with partial pressure PCO2 =0.97 atmosphere, leads to KC=l0-8.52±0.04 and KA= 10-8.36±0.04. Based on these K values, standard free energies of formation of <span class="hlt">calcite</span> and aragonite were calculated to be -270,144±375 and -269,926±375 calories mole-1, (-1,130,282±1,569 and -1,129,370±1,569 joules mole-1), respectively. From the 25°C K values, using appropriate entropy and heat capacity data, values of KC and KA were calculated over the temperature range 0° to 200°C. Possible errors in interpretation of measured pH values and inferred PCO2values and the bearing of these errors on calculations of K values are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6863258','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6863258"><span>Controls of carbonate mineralogy and solid-solution of Mg in <span class="hlt">calcite</span>: evidence from spelean systems</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Gonzalez, L.A.; Lohmann, K.C.</p> <p>1985-01-01</p> <p>Precipitation of carbonate minerals in spelean systems occurs under a wide range of fluid chemistry, Mg-Ca ratios, alkalinities, pH and temperatures; thus, spelean systems provide ideal settings to determine factors controlling the mineralogy of precipitated carbonates and solid-solution of Mg in <span class="hlt">calcite</span>. Cave waters and actively-precipitating carbonate speleothems were collected from Carlsbad Caverns National Park, New Mexico and the Mammoth-Flint Cave System, Kentucky. Carbonate mineralogy of precipitated phases was determined by x-ray diffraction, and major and minor element composition of waters and accompanying minerals were determined by Atomic Absorption Spectrophotometry. Results demonstrate that at a constant CO3 concentration the precipitation threshold for <span class="hlt">calcite</span> to aragonite is controlled dominantly by the Mg/Ca ratio of the ambient fluid. Aragonite precipitation is favored by high Mg/Ca ratios. Conversely, with increasing CO3 concentration at constant fluid Mg/Ca ratios, <span class="hlt">calcite</span> is preferentially precipitated. Solid-solution of Mg in <span class="hlt">calcite</span> is positively correlated with both increased Mg/Ca ratios and CO3 concentrations. These data suggest that Mg contents of <span class="hlt">calcite</span> can not be defined solely in terms of a homogeneous distribution coefficient. Rather, Mg concentrations can be also be affected by the CO3 concentration and degree of <span class="hlt">calcite</span> saturation, suggesting that the rate of <span class="hlt">crystal</span> growth also plays and important role in Mg solid-solution in <span class="hlt">calcites</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26852350','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26852350"><span>Influence of surface conductivity on the apparent zeta potential of <span class="hlt">calcite</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Li, Shuai; Leroy, Philippe; Heberling, Frank; Devau, Nicolas; Jougnot, Damien; Chiaberge, Christophe</p> <p>2016-04-15</p> <p>Zeta potential is a physicochemical parameter of particular importance in describing the surface electrical properties of charged porous media. However, the zeta potential of <span class="hlt">calcite</span> is still poorly known because of the difficulty to interpret streaming potential experiments. The Helmholtz-Smoluchowski (HS) equation is widely used to estimate the apparent zeta potential from these experiments. However, this equation neglects the influence of surface conductivity on streaming potential. We present streaming potential and electrical conductivity measurements on a <span class="hlt">calcite</span> powder in contact with an aqueous NaCl electrolyte. Our streaming potential model corrects the apparent zeta potential of <span class="hlt">calcite</span> by accounting for the influence of surface conductivity and flow regime. We show that the HS equation seriously underestimates the zeta potential of <span class="hlt">calcite</span>, particularly when the electrolyte is diluted (ionic strength ⩽ 0.01 M) because of <span class="hlt">calcite</span> surface conductivity. The basic Stern model successfully predicted the corrected zeta potential by assuming that the zeta potential is located at the outer Helmholtz plane, i.e. without considering a stagnant diffuse layer at the <span class="hlt">calcite</span>-water interface. The surface conductivity of <span class="hlt">calcite</span> <span class="hlt">crystals</span> was inferred from electrical conductivity measurements and computed using our basic Stern model. Surface conductivity was also successfully predicted by our surface complexation model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T43F2715G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T43F2715G"><span>(U-Th)/He dating and He diffusion in <span class="hlt">calcite</span> from veins and breccia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gautheron, C.; Cros, A.; Pagel, M.; Berthet, P.; Tassan-Got, L.; Douville, E.; Pinna-Jamme, R.; Sarda, P.</p> <p>2013-12-01</p> <p>Knowledge of He retention in crystalline <span class="hlt">calcite</span> is mandatory to estimate the possibility of (U-Th)/He dating of <span class="hlt">calcite</span>. To this aim, fault-filling <span class="hlt">calcite</span> <span class="hlt">crystals</span> from the Eocene/Oligocene Gondrecourt graben, Paris Basin, Eastern France, have been sampled, based on their relatively old, Eocene-Oligocene, precipitation age and cold thermal history (<40°C since precipitation). The samples were sorted into three main tectonic and morphological groups, including successively (1) micro-fracture <span class="hlt">calcites</span>, (2) breccia and associated geodic <span class="hlt">calcites</span>, and (3) vein and associated geodic <span class="hlt">calcites</span>. (U-Th)/He dating of 63 <span class="hlt">calcite</span> fragments yields ages dispersed from 0.2×0.02 to 35.8×2.7 Ma, as well as two older dates of 117×10 and 205×28 Ma (1s). These He ages correlate to grain chemistry, such as to Sr and ΣREE concentrations or (La/Yb)N ratios, and these correlations probably reflect the evolution of parent fluid. Only the oldest He ages are in agreement with the He-retentive character of <span class="hlt">calcite</span> as determined by Copeland et al. (2007), and these ages were obtained for the most recently precipitated <span class="hlt">crystals</span>. To better understand the large He-age scatter and why <span class="hlt">calcites</span> precipitated earlier show younger ages, He diffusion experiments have been conducted on 10 Gondrecourt <span class="hlt">calcite</span> fragments from 3 samples with He ages of 0.2 to 6 Ma. In addition, a crystallographic investigation by X-Ray Diffraction (XRD) performed on similar samples reveals that the <span class="hlt">crystal</span> structure evolves with increasing temperature, showing with micro-cracks and cleavage opening. These XRD results indicate that, in fault-filling <span class="hlt">calcite</span>, He retention is controlled by multiple diffusion domains (MDD, Lovera et al., 1991) with various sizes, and therefore, evolves through time with strong consequences on (U-Th)/He age. We thus interpret the Gondrecourt <span class="hlt">calcite</span> (U-Th)/He age scatter of older samples as a consequence of cleavage opening due to a succession of <span class="hlt">calcite</span> <span class="hlt">crystallization</span> phases related to</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_9 --> <div id="page_10" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="181"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28130130','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28130130"><span>Structural studies of a vasorelaxant lectin from Dioclea reflexa Hook <span class="hlt">seeds</span>: <span class="hlt">Crystal</span> structure, molecular docking and dynamics.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pinto-Junior, Vanir Reis; Osterne, Vinicius José Silva; Santiago, Mayara Queiroz; Correia, Jorge Luis Almeida; Pereira-Junior, Francisco Nascimento; Leal, Rodrigo Bainy; Pereira, Maria Gonçalves; Chicas, Larissa Silva; Nagano, Celso Shiniti; Rocha, Bruno Anderson Matias; Silva-Filho, José Caetano; Ferreira, Wandemberg Paiva; Rocha, Cíntia Renata Costa; Nascimento, Kyria Santiago; Assreuy, Ana Maria Sampaio; Cavada, Benildo Sousa</p> <p>2017-05-01</p> <p>The three-dimensional structure of Dioclea reflexa <span class="hlt">seed</span> lectin (DrfL) was studied in detail by a combination of X-ray crystallography, molecular docking and molecular dynamics. DrfL was purified by affinity chromatography using Sephadex G-50 matrix. Its primary structure was obtained by mass spectrometry, and <span class="hlt">crystals</span> belonging to orthorhombic space group P212121 were grown by the vapor diffusion method at 293K. The <span class="hlt">crystal</span> structure was solved at 1.765Å and was very similar to that of other lectins from the same subtribe. The structure presented Rfactor and Rfree of 21.69% and 24.89%, respectively, with no residues in nonallowed regions of Ramachandran plot. Similar to other Diocleinae lectins, DrfL was capable of relaxing aortic rings via NO induction, with CRD participation, albeit with low intensity (32%). In silico analysis results demonstrated that DrfL could strongly interact with complex N-glycans, components of blood vessel glycoconjugates. Despite the high similarity among Diocleinae lectins, it was also reported that each lectin has unique CRD properties that influence carbohydrate binding, resulting in different biological effects presented by these molecules.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23493708','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23493708"><span>Flexible minerals: self-assembled <span class="hlt">calcite</span> spicules with extreme bending strength.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Natalio, Filipe; Corrales, Tomas P; Panthöfer, Martin; Schollmeyer, Dieter; Lieberwirth, Ingo; Müller, Werner E G; Kappl, Michael; Butt, Hans-Jürgen; Tremel, Wolfgang</p> <p>2013-03-15</p> <p>Silicatein-α is responsible for the biomineralization of silicates in sponges. We used silicatein-α to guide the self-assembly of <span class="hlt">calcite</span> "spicules" similar to the spicules of the calcareous sponge Sycon sp. The self-assembled spicules, 10 to 300 micrometers (μm) in length and 5 to 10 μm in diameter, are composed of aligned <span class="hlt">calcite</span> nanocrystals. The spicules are initially amorphous but transform into <span class="hlt">calcite</span> within months, exhibiting unusual growth along [100]. They scatter x-rays like twinned <span class="hlt">calcite</span> <span class="hlt">crystals</span>. Whereas natural spicules evidence brittle failure, the synthetic spicules show an elastic response, which greatly enhances bending strength. This remarkable feature is linked to a high protein content. With nano-thermogravimetric analysis, we measured the organic content of a single spicule to be 10 to 16%. In addition, the spicules exhibit waveguiding properties even when they are bent.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70029387','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70029387"><span>The <span class="hlt">calcite</span> → aragonite transformation in low-Mg marble: Equilibrium relations, transformations mechanisms, and rates</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hacker, Bradley R.; Rubie, David C.; Kirby, Stephen H.; Bohlen, Steven R.</p> <p>2005-01-01</p> <p>Experimental transformation of a rather pure natural <span class="hlt">calcite</span> marble to aragonite marble did not proceed via the expected straightforward polymorphic replacement. Instead, the small amount of Mg in the starting material (0.36 wt %) was excluded from the growing aragonite and diffused preferentially into the remaining <span class="hlt">calcite</span> grains, producing Mg-rich <span class="hlt">calcite</span> rods that persisted as relicts. Nucleation of aragonite occurred exclusively on grain boundaries, with aragonite [001] oriented subparallel to <span class="hlt">calcite</span> [0001]. The aragonite <span class="hlt">crystals</span> preferentially consumed the <span class="hlt">calcite</span> <span class="hlt">crystal</span> on which they nucleated, and the reaction fronts developed preferentially along the {010} and {110} planes of aragonite. Each aragonite neoblast that grew was nearly free of Mg (typically <0.1 wt %). The excess Mg was taken up by the <span class="hlt">calcite</span> grains in between, stabilizing them and causing a few volume percent rodlike relicts of Mg-enriched <span class="hlt">calcite</span> (up to 10 wt % MgO) to be left behind by the advancing reaction front. The aragonite growth rates are approximately linear and range from ∼3 × 10−11 m s−1 at 600°C to ∼9 × 10−9 m s−1 at 850°C, with an apparent activation enthalpy of 166 ± 91 kJ mol−1. This reaction mechanism and the resultant texture are akin to cellular precipitation reactions in metals. Similar transformation textures have been reported from high-Mg marbles in Japan and China that disproportionated to low-Mg <span class="hlt">calcite</span> and dolomite.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26087312','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26087312"><span>Growth and Dissolution of <span class="hlt">Calcite</span> in the Presence of Adsorbed Stearic Acid.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ricci, Maria; Segura, Juan José; Erickson, Blake W; Fantner, Georg; Stellacci, Francesco; Voïtchovsky, Kislon</p> <p>2015-07-14</p> <p>The interaction of organic molecules with the surface of <span class="hlt">calcite</span> plays a central role in many geochemical, petrochemical, and industrial processes and in biomineralization. Adsorbed organics, typically fatty acids, can interfere with the evolution of <span class="hlt">calcite</span> when immersed in aqueous solutions. Here we use atomic force microscopy in liquid to explore in real-time the evolution of the (1014) surface of <span class="hlt">calcite</span> covered with various densities of stearic acid and exposed to different saline solutions. Our results show that the stearic acid molecules tend to act as "pinning points" on the <span class="hlt">calcite</span>'s surface and slow down the <span class="hlt">crystal</span>'s restructuring kinetics. Depending on the amount of material adsorbed, the organic molecules can form monolayers or bilayer islands that become embedded into the growing <span class="hlt">crystal</span>. The growth process can also displaces the organic molecules and actively concentrate them into stacked multilayers. Our results provide molecular-level insights into the interplay between the adsorbed fatty acid molecules and the evolving <span class="hlt">calcite</span> <span class="hlt">crystal</span>, highlighting mechanisms that could have important implications for several biochemical and geochemical processes and for the oil industry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/983508','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/983508"><span>Mechanism of <span class="hlt">Calcite</span> Co-Orientation in the Sea Urchin Tooth</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Killian, Christopher; Metzler, Rebecca; Gong, Y. U. T.; Olson, Ian; Aizenberg, Joanna; Politi, Yael; Wilt, Fred; Scholl, Andreas; Young, Anthony; Doran, Andrew; Kunz, Martin; Tamura, Nobumichi; Coppersmith, Susan; Gilbert, P. U. P. A.</p> <p>2009-12-01</p> <p>Sea urchin teeth are remarkable and complex <span class="hlt">calcite</span> structures, continuously growing at the forming end and self-sharpening at the mature grinding tip. The <span class="hlt">calcite</span> (CaCO{sub 3}) <span class="hlt">crystals</span> of tooth components, plates, fibers, and a high-Mg polycrystalline matrix, have highly co-oriented crystallographic axes. This ability to co-orient <span class="hlt">calcite</span> in a mineralized structure is shared by all echinoderms. However, the physico-chemical mechanism by which <span class="hlt">calcite</span> <span class="hlt">crystals</span> become co-oriented in echinoderms remains enigmatic. Here, we show differences in <span class="hlt">calcite</span> c-axis orientations in the tooth of the purple sea urchin (Strongylocentrotus purpuratus), using high-resolution X-ray photoelectron emission spectromicroscopy (X-PEEM) and microbeam X-ray diffraction ({mu}XRD). All plates share one <span class="hlt">crystal</span> orientation, propagated through pillar bridges, while fibers and polycrystalline matrix share another orientation. Furthermore, in the forming end of the tooth, we observe that CaCO{sub 3} is present as amorphous calcium carbonate (ACC). We demonstrate that co-orientation of the nanoparticles in the polycrystalline matrix occurs via solid-state secondary nucleation, propagating out from the previously formed fibers and plates, into the amorphous precursor nanoparticles. Because amorphous precursors were observed in diverse biominerals, solid-state secondary nucleation is likely to be a general mechanism for the co-orientation of biomineral components in organisms from different phyla.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1184974','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1184974"><span>Heterogeneous growth of cadmium and cobalt carbonate phases at the (101¯4) <span class="hlt">calcite</span> surface</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Xu, Man; Ilton, Eugene S.; Engelhard, Mark H.; Qafoku, Odeta; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien N.</p> <p>2015-03-01</p> <p>The ability of surface precipitates to form heteroepitaxially is an important factor that controls the extent of heterogeneous growth. In this work, the growth of cadmium and cobalt carbonate phases on (10-14) <span class="hlt">calcite</span> surfaces is compared for a range of initial saturation states with respect to otavite (CdCO3) and sphaerocobaltite (CoCO3), two isostructural metal carbonates that exhibit different lattice misfits with respect to <span class="hlt">calcite</span>. <span class="hlt">Calcite</span> single <span class="hlt">crystals</span> were reacted in static conditions for 16 hours with CdCl2 and CoCl2 aqueous solutions with initial concentrations 0.3 ≤ [Cd2+]0 ≤ 100 μM and 25 ≤ [Co2+]0 ≤ 200 μM. The reacted <span class="hlt">crystals</span> were imaged in situ with atomic force microscopy (AFM) and analyzed ex situ with X-ray photoelectron spectroscopy (XPS). AFM images of Cd-reacted <span class="hlt">crystals</span> showed the formation of large islands elongated along the direction, clear evidence of heteroepitaxial growth, whereas surface precipitates on Co-reacted <span class="hlt">crystals</span> were small round islands. Deformation of <span class="hlt">calcite</span> etch pits in both cases indicated the incorporation of Cd and Co at step edges. XPS analysis pointed to the formation of a Cd-rich (Ca,Cd)CO3 solid solution coating atop the <span class="hlt">calcite</span> substrate. In contrast, XPS measurements of the Co-reacted <span class="hlt">crystals</span> provided evidence for the formation of a mixed hydroxy-carbonate cobalt phase. The combined AFM and XPS results suggest that the lattice misfit between CoCO3 and CaCO3 ( 15% based on surface areas) is too large to allow for heteroepitaxial growth of a pure cobalt carbonate phase on <span class="hlt">calcite</span> surfaces in aqueous solutions and at ambient conditions. The use of the satellite structure of the Co 2p3/2 photoelectron line as a tool for determining the nature of cobalt surface precipitates is also discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25233226','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25233226"><span>Nucleation, growth and evolution of calcium phosphate films on <span class="hlt">calcite</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Naidu, Sonia; Scherer, George W</p> <p>2014-12-01</p> <p>Marble, a stone composed of the mineral <span class="hlt">calcite</span>, is subject to chemically induced weathering in nature due to its relatively high dissolution rate in acid rain. To protect monuments and sculpture from corrosion, we are investigating the application of thin layers of hydroxyapatite (HAP) onto marble. The motivation for using HAP is its low dissolution rate and <span class="hlt">crystal</span> and lattice compatibility with <span class="hlt">calcite</span>. A mild, wet chemical synthesis route, in which diammonium hydrogen phosphate salt was reacted with marble, alone and with cationic and anionic precursors under different reaction conditions, was used to produce inorganic HAP layers on marble. Nucleation and growth on the <span class="hlt">calcite</span> substrate was studied, as well as metastable phase evolution, using scanning electron microscopy, grazing incidence X-ray diffraction, and atomic force microscopy. Film nucleation was enhanced by surface roughness. The rate of nucleation and the growth rate of the film increased with cationic (calcium) and anionic (carbonate) precursor additions. Calcium additions also influenced phase formation, introducing a metastable phase (octacalcium phosphate) and a different phase evolution sequence.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23764657','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23764657"><span>On-line near infrared spectroscopy as a Process Analytical Technology (PAT) tool to control an industrial <span class="hlt">seeded</span> API <span class="hlt">crystallization</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Schaefer, C; Lecomte, C; Clicq, D; Merschaert, A; Norrant, E; Fotiadu, F</p> <p>2013-09-01</p> <p>The final step of an active pharmaceutical ingredient (API) manufacturing synthesis process consists of a <span class="hlt">crystallization</span> during which the API and residual solvent contents have to be quantified precisely in order to reach a predefined <span class="hlt">seeding</span> point. A feasibility study was conducted to demonstrate the suitability of on-line NIR spectroscopy to control this step in line with new version of the European Medicines Agency (EMA) guideline [1]. A quantitative method was developed at laboratory scale using statistical design of experiments (DOE) and multivariate data analysis such as principal component analysis (PCA) and partial least squares (PLS) regression. NIR models were built to quantify the API in the range of 9-12% (w/w) and to quantify the residual methanol in the range of 0-3% (w/w). To improve the predictive ability of the models, the development procedure encompassed: outliers elimination, optimum model rank definition, spectral range and spectral pre-treatment selection. Conventional criteria such as, number of PLS factors, R(2), root mean square errors of calibration, cross-validation and prediction (RMSEC, RMSECV, RMSEP) enabled the selection of three model candidates. These models were tested in the industrial pilot plant during three technical campaigns. Results of the most suitable models were evaluated against to the chromatographic reference methods. Maximum relative bias of 2.88% was obtained about API target content. Absolute bias of 0.01 and 0.02% (w/w) respectively were achieved at methanol content levels of 0.10 and 0.13% (w/w). The repeatability was assessed as sufficient for the on-line monitoring of the 2 analytes. The present feasibility study confirmed the possibility to use on-line NIR spectroscopy as a PAT tool to monitor in real-time both the API and the residual methanol contents, in order to control the <span class="hlt">seeding</span> of an API <span class="hlt">crystallization</span> at industrial scale. Furthermore, the successful scale-up of the method proved its capability to be</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140010369','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140010369"><span>Structural Characterization of Lateral-grown 6H-SiC am-plane <span class="hlt">Seed</span> <span class="hlt">Crystals</span> by Hot Wall CVD Epitaxy</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Goue, Ouloide Yannick; Raghothamachar, Balaji; Dudley, Michael; Trunek, Andrew J.; Neudeck, Philip G.; Woodworth, Andrew A.; Spry, David J.</p> <p>2014-01-01</p> <p>The performance of commercially available silicon carbide (SiC) power devices is limited due to inherently high density of screw dislocations (SD), which are necessary for maintaining polytype during boule growth and commercially viable growth rates. The NASA Glenn Research Center (GRC) has recently proposed a new bulk growth process based on axial fiber growth (parallel to the c-axis) followed by lateral expansion (perpendicular to the c-axis) for producing multi-faceted m-plane SiC boules that can potentially produce wafers with as few as one SD per wafer. In order to implement this novel growth technique, the lateral homoepitaxial growth expansion of a SiC fiber without introducing a significant number of additional defects is critical. Lateral expansion is being investigated by hot wall chemical vapor deposition (HWCVD) growth of 6H-SiC am-plane <span class="hlt">seed</span> <span class="hlt">crystals</span> (0.8mm x 0.5mm x 15mm) designed to replicate axially grown SiC single <span class="hlt">crystal</span> fibers. The post-growth <span class="hlt">crystals</span> exhibit hexagonal morphology with approximately 1500 m (1.5 mm) of total lateral expansion. Preliminary analysis by synchrotron white beam x-ray topography (SWBXT) confirms that the growth was homoepitaxial, matching the polytype of the respective underlying region of the <span class="hlt">seed</span> <span class="hlt">crystal</span>. Axial and transverse sections from the as grown <span class="hlt">crystal</span> samples were characterized in detail by a combination of SWBXT, transmission electron microscopy (TEM) and Raman spectroscopy to map defect types and distribution. X-ray diffraction analysis indicates the <span class="hlt">seed</span> <span class="hlt">crystal</span> contained stacking disorders and this appears to have been reproduced in the lateral growth sections. Analysis of the relative intensity for folded transverse acoustic (FTA) and optical (FTO) modes on the Raman spectra indicate the existence of stacking faults. Further, the density of stacking faults is higher in the <span class="hlt">seed</span> than in the grown <span class="hlt">crystal</span>. Bundles of dislocations are observed propagating from the <span class="hlt">seed</span> in m-axis lateral directions</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5859811','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5859811"><span>Intercalation of sea urchin proteins in <span class="hlt">calcite</span>: Study of a crystalline composite material</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Berman, A.; Addadi, L.; Leiserowitz, L.; Weiner, S. ); Kvick, A.; Nelson, M. )</p> <p>1990-11-02</p> <p>Sea urchin skeletal elements are composed of single <span class="hlt">crystals</span> of <span class="hlt">calcite</span>. Unlike their synthetic counterparts, these <span class="hlt">crystals</span> do not have well-developed cleavage and are consequently much more resistant to fracture. This phenomenon is due in part to the presence of acidic glycoproteins occluded within the <span class="hlt">crystals</span>. By means of x-ray diffraction with synchrotron radiation, it is shown that the presence of the protein in synthetic <span class="hlt">calcite</span> only slightly decreases the coherence length but significantly increases the angular spread of perfect domains of the <span class="hlt">crystals</span>. In biogenic <span class="hlt">calcite</span>, the coherence length is 1/3 to 1/4 as much as that in synthetic <span class="hlt">calcite</span> and the angular spread is 20 to 50 times as wide. It is proposed that the presence of macromolecules concentrated at mosaic boundaries that are oblique to cleavage planes is responsible for the change in fracture properties. These results may be important in the material sciences, because of the unusual nature of this material, namely, a composite based on the controlled intercalation of macromolecules inside single-<span class="hlt">crystal</span> lattices. 20 refs., 3 figs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15006787','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15006787"><span>Direct observation of microbial inhibition of <span class="hlt">calcite</span> dissolution.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lüttge, Andreas; Conrad, Pamela G</p> <p>2004-03-01</p> <p>Vertical scanning interferometry (VSI) provides a method for quantification of surface topography at the angstrom to nanometer level. Time-dependent VSI measurements can be used to study the surface-normal retreat across <span class="hlt">crystal</span> and other solid surfaces during dissolution or corrosion processes. Therefore, VSI can be used to directly and nondestructively measure mineral dissolution rates with high precision. We have used this method to compare the abiotic dissolution behavior of a representative <span class="hlt">calcite</span> (CaCO(3)) cleavage face with that observed upon addition of an environmental microbe, Shewanella oneidensis MR-1, to the <span class="hlt">crystal</span> surface. From our direct observations, we have concluded that the presence of the microbes results in a significant inhibition of the rate of <span class="hlt">calcite</span> dissolution. This inhibition appears to be a 2nd-order effect that is related to the formation of etch pits. The opening of etch pits was greatly inhibited in the presence of added bacteria, suggesting that the bacterial cells exert their effect by inhibiting the formation of etch pits at high-energy sites at the <span class="hlt">crystal</span> surface caused by lattice defects, e.g., screw or point dislocations. The experimental methodology thus provides a nondestructive, directly quantifiable, and easily visualized view of the interactions of microbes and minerals during weathering (or corrosion) processes or during mineral precipitation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19840019705','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19840019705"><span>Project Explorer: Get Away Special #007. [alloy solidification, <span class="hlt">seed</span> germination, <span class="hlt">crystal</span> growth, and radio transmission of payload data</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Henderson, A. J., Jr.</p> <p>1984-01-01</p> <p>Tentatively scheduled to fly on STS-17 (41G), this get away special aims to demonstrate amateur radio transmissions to global ground stations in the English language. Experiments No. 1, 2, and 3 use the micro-gravity of space flight to study the solidification of lead-antimony and aluminum-copper alloys, the germination of radish <span class="hlt">seeds</span>, and the growth of potassium-tetracyanoplatinate hydrate <span class="hlt">crystals</span> in an aqueous solution. Flight results are to be compared with Earth-based data. Experiment No. 4 (the Marshall Amateur Radio Club Experiment - MARCE) features radio transmissions and also provides timing for the start of all other experiments. A microprocessor obtains real-time data from all experiments as well as temperature and pressure measurements within the GAS canister. These data are to be transmitted on previously announced amateur radio frequencies after they are converted into the English language by a digitalker for general reception. The support structure for the G #007 experiments consists of two primary plates and four bumper assemblies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17142058','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17142058"><span><span class="hlt">Crystal</span> structure of the anticarcinogenic Bowman-Birk inhibitor from snail medic (Medicago scutellata) <span class="hlt">seeds</span> complexed with bovine trypsin.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Capaldi, Stefano; Perduca, Massimiliano; Faggion, Beniamino; Carrizo, Maria E; Tava, Aldo; Ragona, Laura; Monaco, Hugo L</p> <p>2007-04-01</p> <p>The structure of the ternary complex of the anticarcinogenic Bowman-Birk protease inhibitor purified from snail medic (Medicago scutellata) <span class="hlt">seeds</span> (MSTI) and two molecules of bovine trypsin has been solved by X-ray diffraction analysis of single <span class="hlt">crystals</span> to a resolution of 2.0 A. This is the highest resolution model of a ternary complex of this type currently available. The two binding loops of the MSTI differ in only one amino acid and have in both cases an arginine in position P1. The distances between the residues of the inhibitor at the binding interface and the trypsin side chains that recognize them are almost identical in the two sites. When compared to the NMR model of the uncomplexed MSTI, the inhibitor in the functional assembly with trypsin shows the largest differences in the two P2' residues. Compared with the similar ternary complex of the soybean trypsin inhibitor, this model shows very small differences in the polypeptide chain of the trypsin binding sites and its largest difference in the area between Asp 26 and His 32 of the MSTI which in the soybean inhibitor has an extra Leu inserted in position 29.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFM.B21B0702P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFM.B21B0702P"><span>Alginic Acid Accelerates <span class="hlt">Calcite</span> Dissolution</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Perry, T. D.; Duckworth, O. W.; McNamara, C. J.; Martin, S. T.; Mitchell, R.</p> <p>2003-12-01</p> <p>Accelerated carbonate weathering through biological activity affects both geochemical cycling and the local pH and alkalinity of terrestrial and marine waters. Microbes affect carbonate dissolution through metabolic activity, production of acidic or chelating exudates, and cation binding by cell walls. Dissolution occurs within microbial biofilms - communities of microorganisms attached to stone in an exopolymer matrix. We investigated the effect of alginic acid, a common biological polymer produced by bacteria and algae, on <span class="hlt">calcite</span> dissolution using a paired atomic force microscopy/flow-through reactor apparatus. The alginic acid caused up to an order of magnitude increase in dissolution rate at 3 < pH < 12. Additionally, the polymer preferentially binds to the obtuse pit steps and increases step velocity. We propose that the polymer is actively chelating surficial cations reducing the activation energy and increasing dissolution rate. The role of biologically produced polymers in mineral weathering is important in the protection of cultural heritage materials and understanding of marine and terrestrial systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/930338','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/930338"><span>Coprecipitation of Chromate with <span class="hlt">Calcite</span>: Batch Experiments and X-ray Absorption Spectroscopy</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Tang,Y.; Elzinga, E.; Lee, Y.; Reeder, R.</p> <p>2007-01-01</p> <p>Batch experiments, combined with in situ spectroscopic methods, are used to examine the coprecipitation of Cr(VI) with <span class="hlt">calcite</span>, including partitioning behavior, site-specific distribution of Cr on the surface of <span class="hlt">calcite</span> single <span class="hlt">crystals</span>, and local coordination of Cr(VI) in the <span class="hlt">calcite</span> structure. It is found that the concentration of Cr incorporated in <span class="hlt">calcite</span> increases with increasing Cr concentration in solution. The calculated apparent partition coefficient, K{sub d}*, is highest at low Cr solution concentration, and decreases to a constant value with increasing Cr solution concentration. DIC images of the (1 0 {bar 1} 4) surface of <span class="hlt">calcite</span> single <span class="hlt">crystals</span> grown in the presence of CrO{sub 4}{sup 2-}exhibit well-defined growth hillocks composed of two pairs of symmetrically nonequivalent vicinal faces, denoted as + and -, which reflect the orientation of structurally nonequivalent growth steps. Micro-XRF mapping of the Cr distribution over a growth hillock shows preferential incorporation of Cr into the -- steps, which is considered to result from differences in surface structure geometry. XANES spectra confirm that incorporated Cr is hexavalent, and no reduction of Cr(VI) in the X-ray beam was observed up to 2 days at room temperature. EXAFS fit results show the incorporated Cr(VI) has the expected first shell of 4 O at {approx}1.64 {+-} 0.01 {angstrom}, consistent with CrO{sub 4}{sup 2-}. Best fit results show that the second shell is split with {approx}2.5 Ca at {approx}3.33 {+-} 0.05 and {approx}2.2 Ca at 3.55 {+-} 0.05 {angstrom}, which confirms the incorporation of chromate into <span class="hlt">calcite</span>. Consideration of possible local coordination indicates that significant distortion or disruption is required to accommodate CrO{sub 4}{sup 2-}in the <span class="hlt">calcite</span> structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20110889','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20110889"><span>Comparison of dissolution and surface reactions between <span class="hlt">calcite</span> and aragonite in L-glutamic and L-aspartic acid solutions.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ryu, Miyoung; Kim, Hwan; Lim, Mihee; You, Kwangsuk; Ahn, Jiwhan</p> <p>2010-01-11</p> <p>We have investigated dissolution and surface reaction of <span class="hlt">calcite</span> and aragonite in amino acid solutions of L-glutamic (L-glu) and L-aspartic acid (L-asp) at weak acidity of above pH 3. The surface reactions of <span class="hlt">calcite</span> and aragonite were related with the dissolution. <span class="hlt">Calcite</span> was dissolved in both solutions but the dissolution was limited by an adsorption of Ca-carboxylate salt. Aragonite was neither dissolved nor reacted in amino acid solutions because the <span class="hlt">crystal</span> surface consisted of a hard to dissolve structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeCoA.125..528H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeCoA.125..528H"><span>Trace concentration - Huge impact: Nitrate in the <span class="hlt">calcite</span>/Eu(III) system</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hofmann, Sascha; Voïtchovsky, Kislon; Schmidt, Moritz; Stumpf, Thorsten</p> <p>2014-01-01</p> <p>The interactions of trivalent lanthanides and actinides with secondary mineral phases such as <span class="hlt">calcite</span> is of high importance for the safety assessment of deep geological repositories for high level nuclear waste (HLW). Due to similar ionic radii, calcium-bearing mineral phases are suitable host minerals for Ln(III) and An(III) ions. Especially <span class="hlt">calcite</span> has been proven to retain these metal ions effectively by both surface complexation and bulk incorporation. Since anionic ligands (e.g., nitrate) are omnipresent in the geological environment and due to their coordinating properties, their influence on retentive processes should not be underestimated. Nitrate is a common contaminant in most HLW forms as a result of using nitric acid in fuel reprocessing. It is also formed by microbial activity under aerobic conditions. In this study, atomic force microscopy investigations revealed a major influence of nitrate upon the surface of <span class="hlt">calcite</span> <span class="hlt">crystals</span>. NaNO3 causes serious modifications even in trace amounts (<10-7 M) and forms a soft surface layer of low crystallinity on top of the <span class="hlt">calcite</span> <span class="hlt">crystal</span>. Time-resolved laser fluorescence spectroscopy of Eu(III) showed that, within this layer, Eu(III) ions are incorporated, while losing most of their hydration shell. The results show that solid solution modelling for actinides in <span class="hlt">calcite</span> must take into account the presence of nitrate in pore and ground waters.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFM.B41C0216C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFM.B41C0216C"><span>Preliminary Results of Bacteria Distribution in Chinese Loess and Their Control on the <span class="hlt">Calcite</span> Formation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, Y.; Lian, B.; Hu, Q.; Teng, H. H.; Wu, T.; Ji, J.; Chen, J.</p> <p>2005-12-01</p> <p>Continuous loess-paleosol sequences on the Chinese Loess Plateau are viewed as one of best continental archives of paleoclimatic and paleoenvironmental changes of the Late Cenozoic era. Carbonate, mainly <span class="hlt">calcite</span>, commonly occurs throughout the entire sequence; though some are detrital, most are in-situ pedogenic. TEM studies have shown various morphologies of <span class="hlt">calcites</span> in Chinese loess, especially nano-rod <span class="hlt">calcite</span> widely occurring in loess and paleosols which are biogenic. In this study, we collected fresh and undisturbed loess and paleosol samples and successfully separated dominant microbial communities. These microbes are mainly bacteria, especially Bacillus anthracis, and a few fungi. The amount of bacteria decreases sharply with the depth. Then we added the bacteria into the near saturated solution of CaCl2 and Na2CO3. It is interesting that the original <span class="hlt">calcite</span> <span class="hlt">crystals</span> formed under abiotic conditions changed from quadrilateral face to pentagonal or hexagonal and the <span class="hlt">crystal</span> size enlarged almost twice. SEM and AFM observations display bacteria control on the growth of <span class="hlt">calcite</span>, which cause the lighter carbon isotopic ratios.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011GeCoA..75.1799O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011GeCoA..75.1799O"><span>Do organic ligands affect <span class="hlt">calcite</span> dissolution rates?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Oelkers, Eric H.; Golubev, Sergey V.; Pokrovsky, Oleg S.; Bénézeth, Pascale</p> <p>2011-04-01</p> <p>Steady state Iceland-spar <span class="hlt">calcite</span> dissolution rates were measured at 25 °C in aqueous solutions containing 0.1 M NaCl and up to 0.05 M dissolved bicarbonate at pH from 7.9 to 9.1 in the presence of 13 distinct dissolved organic ligands in mixed-flow reactors. The organic ligands considered in this study include those most likely to be present in either (1) aquifers at the conditions pertinent to CO 2 sequestration or (2) soil/early diagenetic environments: acetate, phthalate, citrate, EDTA 4-, succinate, D-glucosaminate, L-glutamate, D-gluconate, 2,4-dihydroxybenzoate, 3,4-dihydroxybenzoate, fumarate, malonate, and gallate. Results show that the presence of <0.05 mol/kg of these organic anions changes <span class="hlt">calcite</span> dissolution rates by less than a factor of 2.5 with the exception of citrate and EDTA 4-. The presence of 0.05 mol/kg citrate and EDTA 4- increases <span class="hlt">calcite</span> dissolution rates by as much as a factor of 35 and 500, respectively, compared to rates in organic anion-free solutions. Further <span class="hlt">calcite</span> dissolution experiments were performed in the presence of organic polymers similar to bacterial exudates, cell exopolysaccharides, and analogs of microbial cell envelopes: alginate, lichen extract, humic acid, pectin, and gum xanthan. In no case did the presence of <100 ppm of these organics change <span class="hlt">calcite</span> dissolution rates by more than a factor of 2.5. Results obtained in this study suggest that the presence of aqueous organic anions negligibly affects <span class="hlt">calcite</span> forward dissolution rates in most natural environments. Some effect on <span class="hlt">calcite</span> reactivity may be observed, however, by the presence of organic anions if they change substantially the chemical affinity of the fluid with respect to <span class="hlt">calcite</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11401383','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11401383"><span>Channel Flow Cell Studies of the Inhibiting Action of Gypsum on the Dissolution Kinetics of <span class="hlt">Calcite</span>: A Laboratory Approach with Implications for Field Monitoring.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wilkins, Shelley J.; Compton, Richard G.; Taylor, Mark A.; Viles, Heather A.</p> <p>2001-04-15</p> <p>The rate of dissolution of surface-treated <span class="hlt">calcite</span> <span class="hlt">crystals</span> in aqueous acidic solution has been studied using an adaptation of the channel flow cell method with microdisc electrode detection. Surface treatments of <span class="hlt">calcite</span> with sulfuric acid lead to the nucleation of gypsum overgrowths, which reduce the rate of dissolution of <span class="hlt">calcite</span>. Rate constants for untreated <span class="hlt">calcite</span> and <span class="hlt">calcite</span> pretreated with sulfuric acid conditions of 0.01 M for 1 h, 0.05 M for 5 h, and 0.1 M for 21 h are found to be 0.035, 0.018, 0.006, and 0.004 cm s(-1), respectively. Deterioration of <span class="hlt">calcite</span> materials caused by acid deposition was investigated by field exposure of untreated and sulfate pretreated <span class="hlt">calcite</span> rocks under urban conditions for 12 months. The rate constant for both pretreated and untreated <span class="hlt">calcite</span> exposed to weathering is 0.003 cm s(-1). This suggests that <span class="hlt">calcite</span> self-passivates the surface from further reaction when exposed to acid deposition. However, surface studies indicate that the surface undergoes erosion and dissolution before passivation. Pretreatment of the surface with sulfate protects the surface from acid deposition so it remains less reactive toward acid compared with untreated <span class="hlt">calcite</span>. Copyright 2001 Academic Press.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_10 --> <div id="page_11" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="201"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/884762','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/884762"><span>Acceleration of <span class="hlt">calcite</span> kinetics by abalone nacre proteins</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Fu, G; Qiu, S R; Orme, C A; Morse, D E; De Yoreo, J J</p> <p>2005-06-09</p> <p>The fascinating shapes and hierarchical designs of biomineralized structures have long been an inspiration to materials scientists because of the potential they suggest for biomolecular control over synthesis of crystalline materials. One prevailing view is that mineral-associated macromolecules are responsible for initiating and stabilizing non-equilibrium <span class="hlt">crystal</span> polymorphs and morphologies through interactions between anionic moieties and cations in solution or at mineral surfaces. Indeed, numerous studies have demonstrated that bio-organic additives can dramatically alter <span class="hlt">crystal</span> shapes and growth-rates in vitro. However, previous molecular-scale studies revealing mechanisms of growth modification focused on small molecules such as amino acids or peptides and always observed growth inhibition. In contrast, studies using full proteins were non-quantitative and underlying sources of growth modification were ill-defined. Here we investigate interactions between proteins isolated from abalone shell nacre and growing surfaces of <span class="hlt">calcite</span>. We find that these proteins significantly accelerate the molecular-scale kinetics and, though much larger than atomic steps, alter growth morphology through step-specific interactions that lower their free energies. We propose that these proteins act as surfactants to promote ion attachment at <span class="hlt">calcite</span> surfaces.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24718337','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24718337"><span>Effect of hydraulic retention time and <span class="hlt">seed</span> material on phosphorus recovery and <span class="hlt">crystal</span> size from urine in an air-agitated reactor.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Liu, Xiaoning; Hu, Zhengyi; Wang, Jinzhi; Wen, Guoqi</p> <p>2014-01-01</p> <p>Phosphorus (P) recovery from urine is affected by various parameters. This study evaluates the effects of hydraulic retention time (HRT) and <span class="hlt">seed</span> material on P recovery and <span class="hlt">crystal</span> size in an air-agitated reactor. Results show that ortho-phosphate removal and struvite recovery efficiencies were 96.3% and 89.5%, and 97.1% and 93.0%, after five runs of HRTs of 1 and 2 h, respectively. Low loss of <span class="hlt">crystals</span> from effluent urine solutions indicates high struvite recovery efficiency and is correlated with the structure and design of the reactor. The average particle size decreased from 40.0 to 31.7 μm as the HRT increased from 1 to 2 h. The two types of <span class="hlt">seed</span> materials (zeolite and molecular sieve) did not affect the ortho-phosphate removal efficiency but affected the struvite <span class="hlt">crystal</span> size. In particular, multi-stage addition of zeolites increased the average <span class="hlt">crystal</span> size from 33.7 to 57.0 μm.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22577807','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22577807"><span>Top-<span class="hlt">seeded</span> solution <span class="hlt">crystal</span> growth of noncentrosymmetric and polar Zn{sub 2}TeMoO{sub 7} (ZTM)</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Zhang, Weiguo; Halasyamani, P. Shiv</p> <p>2016-04-15</p> <p>A top-<span class="hlt">seeded</span> solution growth (TSSG) method was used to grow large, centimeter size, <span class="hlt">crystals</span> of Zn{sub 2}TeMoO{sub 7} (ZTM) – a noncentrosymmetric and polar material. A TeO{sub 2}–MoO{sub 3} mixture in combination with the parent compound was used as a flux. The morphologies of the <span class="hlt">crystals</span> can be controlled by different rotation speeds. Optical spectra indicate that ZTM is transparent up to 5.25 µm with a UV absorption edge of 300 nm. In addition, the refractive index along the optical x, y, and z axes was measured at different wavelengths. - Highlights: • Zn{sub 2}TeMo{sub 2}O{sub 7} <span class="hlt">crystals</span> were grown by top-<span class="hlt">seeded</span> solution growth (TSSG) method. • The morphology of the single <span class="hlt">crystals</span> is controllable by changing rotation speed. • Optical transmission spectra indicate Zn{sub 2}TeMo{sub 2}O{sub 7} has a broad transmission range. • Refractive index along optical axes was measured at different wavelengths.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1087499','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1087499"><span>Upscaling <span class="hlt">Calcite</span> Growth Rates from the Mesoscale to the Macroscale</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bracco, Jacquelyn N.; Stack, Andrew G.; Steefel, Carl I.</p> <p>2013-07-02</p> <p>Quantitative prediction of mineral reaction rates in the subsurface remains a daunting task partly because a key parameter for macroscopic models, the reactive site density, is poorly constrained. Here we report atomic force microscopy (AFM) measurements on the <span class="hlt">calcite</span> surface of monomolecular step densities, treated as equivalent to the reactive site density, as a function of aqueous calcium-to-carbonate ratio and saturation index. Data for the obtuse step orientation are combined with existing step velocity measurements to generate a model that predicts overall macroscopic <span class="hlt">calcite</span> growth rates. The model is quantitatively consistent with several published macroscopic rates under a range of alkaline solution conditions, particularly for two of the most comprehensive data sets without the need for additional fit parameters. The model reproduces peak growth rates and its functional form is simple enough to be incorporated into reactive transport or other macroscopic models designed for predictions in porous media. However, it currently cannot model equilibrium, pH effects, and may overestimate rates at high aqueous calcium-to-carbonate ratios. The discrepancies in rates at high calcium-to-carbonate ratios may be due to differences in pre-treatment, such as exposing the <span class="hlt">seed</span> material to SI 1.0 to generate/develop growth hillocks, or other factors.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26479157','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26479157"><span>The <span class="hlt">Crystal</span> Hotel: A Microfluidic Approach to Biomimetic <span class="hlt">Crystallization</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gong, Xiuqing; Wang, Yun-Wei; Ihli, Johannes; Kim, Yi-Yeoun; Li, Shunbo; Walshaw, Richard; Chen, Li; Meldrum, Fiona C</p> <p>2015-12-02</p> <p>A "<span class="hlt">crystal</span> hotel" microfluidic device that allows <span class="hlt">crystal</span> growth in confined volumes to be studied in situ is used to produce large <span class="hlt">calcite</span> single <span class="hlt">crystals</span> with predefined crystallographic orientation, microstructure, and shape by control of the detailed physical environment, flow, and surface chemistry. This general approach can be extended to form technologically important, nanopatterned single <span class="hlt">crystals</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V33G..04G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V33G..04G"><span>Hydro-gel environment and solution additives modify <span class="hlt">calcite</span> growth mechanism to an accretion process of amorphous nanospheres</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gal, A.; Kahil, K.; Habraken, W.; Gur, D.; Fratzl, P.; Addadi, L.; Weiner, S.</p> <p>2013-12-01</p> <p>Various biominerals form via the transformation of a transient amorphous precursor phase into a mature crystalline phase. The mature biominerals usually exhibit morphology reminiscent of aggregated nanoparticles. Although these observations suggest an accretion-based growth process consisting on nanoparticles, the key factors that control the accretion process are unknown. We investigated the transformation of solid amorphous calcium carbonate (ACC) into <span class="hlt">calcite</span>. When plant cystoliths, a biogenic stable ACC phase, are transformed into <span class="hlt">calcite</span> in vitro by immersion in water, <span class="hlt">calcite</span> <span class="hlt">crystals</span> grow in two distinct steps (Gal et al., Angewandte Chemie, 2013). First, rhombohedral <span class="hlt">crystals</span> grow that show flat facets as expected from ion-by-ion growth. These <span class="hlt">crystals</span> then grow by the aggregation and <span class="hlt">crystallization</span> of the original ACC nanospheres leading to a surface morphology dominated by aggregated spheres. The transformation process occurs within an organic hydro-gel that originates from inside the cystoliths. We tested the importance of the gel phase to the transformation process by transforming synthetic ACC into <span class="hlt">calcite</span> inside various gels. In all the investigated systems: in gelatin, agarose, and pectin gels, <span class="hlt">calcite</span> <span class="hlt">crystals</span> grew that showed the nanosphere aggregation morphology. In additional experiments we demonstrated that also other additives, such as phosphate ions and biogenic macromolecules, that slow down ACC dissolution and <span class="hlt">calcite</span> precipitation from ions can induce the accretion process dominance (see figure attached). These experiments show that although in solution the dominant process is dissolution to ions of the ACC and <span class="hlt">crystal</span> growth by ion-by-ion mechanism, the presence of an additive that slows the ion-mediated processes makes the ACC nanospheres stable long enough to interact with the <span class="hlt">crystal</span> surface. As a result, the metastable ACC nanospheres undergo secondary nucleation on the <span class="hlt">crystal</span> surface without dissolving. These experiments highlight</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1995PhyC..246..253S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1995PhyC..246..253S"><span>Growth of large-domain YBa 2Cu 3O x with new <span class="hlt">seeding</span> <span class="hlt">crystals</span> of CaNdAlO 4 and SrLaGaO 4</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shi, Donglu; Lahiri, K.; Hull, J. R.; LeBlanc, D.; LeBlanc, M. A. R.; Dabkowski, Antoni; Chang, Y.; Jiang, Y.; Zhang, Z.; Fan, H.</p> <p>1995-02-01</p> <p>Single <span class="hlt">crystals</span> of CaNdAlO 4 and SrLaGaO 4 were used as <span class="hlt">seeds</span> to grow large domains of YBa 2Cu 3O x for levitation applications. These <span class="hlt">crystals</span> have high melting temperatures (> 1500°C) and similar lattice structures to that of YBa 2Cu 3O x. In a <span class="hlt">seeded</span> melt-texturing method developed previously, the single <span class="hlt">crystals</span> of CaNdAlO 4, SrLaGaO 4, and NdBa 2Cu 3O x were used as <span class="hlt">seeds</span> for comparison. After melt processing, scanning electron microscopy analysis did not reveal any major differences in all these <span class="hlt">seeded</span> melt-textured samples. However, the levitation forces in the samples <span class="hlt">seeded</span> with single <span class="hlt">crystals</span> of CaNdAlO 4 and SrLaGaO 4 increased considerably compared to that of the sample <span class="hlt">seeded</span> with NdBa 2Cu 3O x. A model is proposed to describe the domain growth mechanism during <span class="hlt">seeded</span> melt processing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/20003982','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/20003982"><span><span class="hlt">Calcite</span> dissolution in two deep eutrophic lakes</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ramisch, F.; Dittrich, M.; Mattenberger, C.; Wehrli, B.; Wueest, A.</p> <p>1999-10-01</p> <p>The calcium cycle, in particular carbonate dissolution, was analyzed in two deep eutrophic lakes, Lago di Lugano (288 m maximum depth) and Sempachersee (87 m) located in Switzerland. A box model approach was used to calculate <span class="hlt">calcite</span> dissolution in the water column and at the sediment-water interface based on various lake monitoring data such as sediment traps, sediment cores, water and pore-water interface based on various lake monitoring data such as sediment traps, sediment cores, water and pore-water analysis. A model for stationary conditions allowing the calculation of <span class="hlt">calcite</span> dissolution in the water column for a given particle size distribution was developed. The relative values of the simulated flux were consistent with sediment trap observations. The best fit of the dissolution rate constant of sinking <span class="hlt">calcite</span> in Lago di Lugano was on the same order of magnitude (3 {center{underscore}dot} 10{sup {minus}10} kg{sup 1/3} s{sup {minus}1}) as published laboratory values for this surface controlled process. Both lakes show a similar specific <span class="hlt">calcite</span> precipitation rate of 170 g Ca m{sup {minus}2} a{sup {minus}1}. The diffusive flux across the sediment-water interface amounts to about 15 and 10% of total <span class="hlt">calcite</span> precipitation in Sempachersee and Lago di Lugano, respectively. However, 61% of the precipitated <span class="hlt">calcite</span> is dissolved in the water column of Lago di Lugano compared to only 13% in Sempachersee. These results point towards the importance of grain size distributions and settling times in stratified deep waters as the two most important factors determining <span class="hlt">calcite</span> retention in sediments of hard water lakes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/wri/2001/wri01-4049/','USGSPUBS'); return false;" href="https://pubs.usgs.gov/wri/2001/wri01-4049/"><span>Ages and Origins of <span class="hlt">Calcite</span> and Opal in the Exploratory Studies Facility Tunnel, Yucca Mountain, Nevada</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Paces, James B.; Neymark, Leonid A.; Marshall, Brian D.; Whelan, Joseph F.; Peterman, Zell E.</p> <p>2001-01-01</p> <p>Deposits of <span class="hlt">calcite</span> and opal are present as coatings on open fractures and lithophysal cavities in unsaturated-zone tuffs at Yucca Mountain, Nevada, site of a potential high-level radioactive waste repository. Outermost layers of <span class="hlt">calcite</span> and opal have radiocarbon ages of 16,000 to 44,000 years before present and thorium-230/uranium ages of 28,000 to more than 500,000 years before present. These ages are young relative to the 13-million-year age of the host rocks. Multiple subsamples from the same outer layer typically show a range of ages with youngest ages from the thinnest subsamples. Initial uranium-234/uranium-238 activity ratios between 1 and 9.5 show a distinct negative correlation with thorium-230/uranium age and are greater than 4 for all but one sample younger than 100,000 years before present. These data, along with micrometer-scale layering and distinctive <span class="hlt">crystal</span> morphologies, are interpreted to indicate that deposits formed very slowly from water films migrating through open cavities. Exchanges of carbon dioxide and water vapor probably took place between downward-migrating liquids and upward-migrating gases at low rates, resulting in oversaturation of mineral constituents at <span class="hlt">crystal</span> extremities and more or less continuous deposition of very thin layers. Therefore, subsamples represent mixtures of older and younger layers on a scale finer than sampling techniques can resolve. Slow, long-term rates of deposition (less than about 5 millimeters of mineral per million years) are inferred from subsamples of outermost <span class="hlt">calcite</span> and opal. These growth rates are similar to those calculated assuming that total coating thicknesses of 10 to 40 millimeters accumulated over 12 million years. <span class="hlt">Calcite</span> has a wide range of delta carbon-13 values from about -8.2 to 8.5 per mil and delta oxygen-18 values from about 10 to 21 per mil. Systematic microsampling across individual mineral coatings indicates basal (older) <span class="hlt">calcite</span> tends to have the largest delta carbon-13 values</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006GeCoA..70.2253L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006GeCoA..70.2253L"><span>The role of citrate and phthalate during Co(II) coprecipitation with <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Young J.; Reeder, Richard J.</p> <p>2006-05-01</p> <p>The influence of citrate and phthalate on Co coprecipitation with <span class="hlt">calcite</span> was investigated using a combination of batch experiments, Fourier-transform infra-red (FT-IR) spectroscopy, and thermogravimetric analysis (TGA) over a wide range of precipitation rates. Steady-state growth conditions (at constant [Ca], [Co], DIC, and pH) were generally achieved within 3-5 h, after which Co(II) partitioning into <span class="hlt">calcite</span> was evaluated. Only minor differences are observed in the partition coefficient ( Kd) trends with and without citrate and phthalate as a function of <span class="hlt">calcite</span> precipitation rate except at very low rates. Slight inhibition of <span class="hlt">calcite</span> growth is observed in the presence of citrate or phthalate, which can be attributed to adsorption at surface sites. TGA curves for samples coprecipitated with citrate show a significant mass loss between 375 and 550 °C, whereas the weight-loss curves for the Co-phthalate coprecipitates are indistinguishable from those of the organic-free Co coprecipitates. This indicates that citrate is incorporated into <span class="hlt">calcite</span> during <span class="hlt">calcite</span> <span class="hlt">crystallization</span>, whereas phthalate is excluded. FT-IR spectra for the sample with citrate show a broad absorption in the range 3700-3100 cm -1, which is attributable to water molecules coordinated to citrate coprecipitated with <span class="hlt">calcite</span>. The preferential incorporation of citrate over phthalate likely reflects differences in both aqueous speciation and conformation of the carboxylate groups. This new finding may provide new insight to the factors that control the behavior of macromolecules and their incorporation into the structure of calcium carbonate during biomineralization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4852989','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4852989"><span>Silver as <span class="hlt">Seed</span>-Particle Material for GaAs Nanowires—Dictating <span class="hlt">Crystal</span> Phase and Growth Direction by Substrate Orientation</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p></p> <p>2016-01-01</p> <p>Here we investigate the feasibility of silver as <span class="hlt">seed</span>-particle material to synthesize GaAs nanowires and show that both <span class="hlt">crystal</span> phase and growth direction can be controlled by choice of substrate orientation. A (111)B substrate orientation can be used to form vertically aligned wurtzite GaAs nanowires and a (100) substrate orientation to form vertically aligned zinc blende GaAs nanowires. A 45–50% yield of vertical nanowire growth is achieved on the (100) substrate orientation without employing any type of surface modification or nucleation strategy to promote a vertical growth direction. In addition, photoluminescence measurements reveal that the photon emission from the silver <span class="hlt">seeded</span> wurtzite GaAs nanowires is characterized by a single and narrow emission peak at 1.52 eV. PMID:26998550</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006cosp...36..521S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006cosp...36..521S"><span>Search for past life on Mars: Physical and chemical characterization of <span class="hlt">calcite</span> minerals of biotic and abiotic origin</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stalport, S.; Coll, C.; Cabane, C.; Navarro González, N. G.; Raulin, R.; Vaulay, V.; Ausset, A.; Szopa, S.; McKay, M.</p> <p></p> <p>Several lines of evidence suggest that early Mars once had liquid water on its surface a denser atmosphere and a mild climate Similar environmental conditions led to the origin of life on the Earth more than 3 5 billion years ago consequently life might also have originated on Mars We contend that inorganic compounds could give us interesting clues as to the existence of possible biological activity in future astrobiological missions to Mars Consequently we have investigated the physical and chemical properties of <span class="hlt">calcite</span> which could be expected on Mars because liquid water was certainly present on the surface of early Mars and carbon dioxide was abundant in its atmosphere <span class="hlt">Calcite</span> is interesting because on Earth this mineral is produced by abiotic processes as well as by biological activity One may suppose that crystalline defects and trace element in the <span class="hlt">crystal</span> lattice and the growth speed of biotic <span class="hlt">calcites</span> must indicate a difference between them and pure abiotic <span class="hlt">calcites</span> We investigated twelve different terrestrial <span class="hlt">calcite</span> samples from various origins biotic diagenetic and abiotic The minerals were studied by X-ray diffraction and electron scanning microscopy to determine their mineralogical and chemical composition and differential thermal analysis coupled to thermogravimetric analysis DTA-TG to determine their thermal behavior Our results show that the thermal degradation of abiotic <span class="hlt">calcite</span> starts at a temperature at least 40oC higher than the degradation temperature of any biotic <span class="hlt">calcite</span> investigated Consequently in the case of a Martian in-situ</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011GeCoA..75.3956D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011GeCoA..75.3956D"><span>Oxygen isotopes in <span class="hlt">calcite</span> grown under cave-analogue conditions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Day, C. C.; Henderson, G. M.</p> <p>2011-07-01</p> <p>Speleothem oxygen isotopes and growth rates are valuable proxies for reconstructing climate history. There is debate, however, about the conditions that allow speleothems to grow in oxygen isotope equilibrium, and about the correct equilibrium fractionation factors. We report results from a series of carbonate growth experiments in karst-analogue conditions in the laboratory. The setup closely mimics natural processes (e.g. precipitation driven by CO 2-degassing, low ionic strength solution, thin solution film) but with a tight control on growth conditions (temperature, pCO 2, drip rate, <span class="hlt">calcite</span> saturation index and the composition of the initial solution). <span class="hlt">Calcite</span> is dissolved in water in a 20,000 ppmV pCO 2 environment. This solution is dripped onto glass plates (coated with <span class="hlt">seed</span>-carbonate) in a lower pCO 2 environment (<2500 ppmV), where degassing leads to <span class="hlt">calcite</span> growth. Experiments were performed at 7, 15, 25 and 35 °C. At each temperature, <span class="hlt">calcite</span> was grown at three drip rates (2, 6 and 10 drips per minute) on separate plates. The mass of <span class="hlt">calcite</span> grown in these experiments varies with temperature ( T in K) and drip rate ( d_ r in drips min -1) according to the relationship daily growth mass = 1.254 + 1.478 ∗ 10 -9 ∗ e0.0679 T + ( e0.00248 T - 2) ∗ (-0.779 d_ r2 + 10.05 d_ r + 11.69). This relationship indicates a substantial increase of growth mass with temperature, a smaller influence of drip rate on growth mass at low temperature and a non-linear relationship between drip rate and growth mass at higher temperatures. Low temperature, fast dripping conditions are found to be the most favourable for reducing effects associated with evaporation and rapid depletion of the dissolved inorganic carbon reservoir (rapid DIC-depletion). The impact of evaporation can be large so caves with high relative humidity are also preferable for palaeoclimate reconstruction. Even allowing for the maximum offsets that may have been induced by evaporation and rapid DIC</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27282839','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27282839"><span>The Alkaline Dissolution Rate of <span class="hlt">Calcite</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Colombani, Jean</p> <p>2016-07-07</p> <p>Due to the widespread presence of calcium carbonate on Earth, several geochemical systems, among which is the global CO2 cycle, are controlled to a large extent by the dissolution and precipitation of this mineral. For this reason, the dissolution of <span class="hlt">calcite</span> has been thoroughly investigated for decades. Despite this intense activity, a consensual value of the dissolution rate of <span class="hlt">calcite</span> has not been found yet. We show here that the inconsistency between the reported values stems mainly from the variability of the chemical and hydrodynamic conditions of measurement. The spreading of the values, when compared in identical conditions, is much less than expected and is interpreted in terms of sample surface topography. This analysis leads us to propose benchmark values of the alkaline dissolution rate of <span class="hlt">calcite</span> compatible with all the published values, and a method to use them in various chemical and hydrodynamic contexts.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040125138&hterms=Amino+acids&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DAmino%2Bacids','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040125138&hterms=Amino+acids&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DAmino%2Bacids"><span>Selective adsorption of L- and D-amino acids on <span class="hlt">calcite</span>: Implications for biochemical homochirality</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hazen, R. M.; Filley, T. R.; Goodfriend, G. A.</p> <p>2001-01-01</p> <p>The emergence of biochemical homochirality was a key step in the origin of life, yet prebiotic mechanisms for chiral separation are not well constrained. Here we demonstrate a geochemically plausible scenario for chiral separation of amino acids by adsorption on mineral surfaces. <span class="hlt">Crystals</span> of the common rock-forming mineral <span class="hlt">calcite</span> (CaCO(3)), when immersed in a racemic aspartic acid solution, display significant adsorption and chiral selectivity of d- and l-enantiomers on pairs of mirror-related <span class="hlt">crystal</span>-growth surfaces. This selective adsorption is greater on <span class="hlt">crystals</span> with terraced surface textures, which indicates that d- and l-aspartic acid concentrate along step-like linear growth features. Thus, selective adsorption of linear arrays of d- and l-amino acids on <span class="hlt">calcite</span>, with subsequent condensation polymerization, represents a plausible geochemical mechanism for the production of homochiral polypeptides on the prebiotic Earth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatCo...713524G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatCo...713524G"><span>3D visualization of additive occlusion and tunable full-spectrum fluorescence in <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Green, David C.; Ihli, Johannes; Thornton, Paul D.; Holden, Mark A.; Marzec, Bartosz; Kim, Yi-Yeoun; Kulak, Alex N.; Levenstein, Mark A.; Tang, Chiu; Lynch, Christophe; Webb, Stephen E. D.; Tynan, Christopher J.; Meldrum, Fiona C.</p> <p>2016-11-01</p> <p>From biomineralization to synthesis, organic additives provide an effective means of controlling <span class="hlt">crystallization</span> processes. There is growing evidence that these additives are often occluded within the <span class="hlt">crystal</span> lattice. This promises an elegant means of creating nanocomposites and tuning physical properties. Here we use the incorporation of sulfonated fluorescent dyes to gain new understanding of additive occlusion in <span class="hlt">calcite</span> (CaCO3), and to link morphological changes to occlusion mechanisms. We demonstrate that these additives are incorporated within specific zones, as defined by the growth conditions, and show how occlusion can govern changes in <span class="hlt">crystal</span> shape. Fluorescence spectroscopy and lifetime imaging microscopy also show that the dyes experience unique local environments within different zones. Our strategy is then extended to simultaneously incorporate mixtures of dyes, whose fluorescence cascade creates <span class="hlt">calcite</span> nanoparticles that fluoresce white. This offers a simple strategy for generating biocompatible and stable fluorescent nanoparticles whose output can be tuned as required.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5120221','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5120221"><span>3D visualization of additive occlusion and tunable full-spectrum fluorescence in <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Green, David C.; Ihli, Johannes; Thornton, Paul D.; Holden, Mark A.; Marzec, Bartosz; Kim, Yi-Yeoun; Kulak, Alex N.; Levenstein, Mark A.; Tang, Chiu; Lynch, Christophe; Webb, Stephen E. D.; Tynan, Christopher J.; Meldrum, Fiona C.</p> <p>2016-01-01</p> <p>From biomineralization to synthesis, organic additives provide an effective means of controlling <span class="hlt">crystallization</span> processes. There is growing evidence that these additives are often occluded within the <span class="hlt">crystal</span> lattice. This promises an elegant means of creating nanocomposites and tuning physical properties. Here we use the incorporation of sulfonated fluorescent dyes to gain new understanding of additive occlusion in <span class="hlt">calcite</span> (CaCO3), and to link morphological changes to occlusion mechanisms. We demonstrate that these additives are incorporated within specific zones, as defined by the growth conditions, and show how occlusion can govern changes in <span class="hlt">crystal</span> shape. Fluorescence spectroscopy and lifetime imaging microscopy also show that the dyes experience unique local environments within different zones. Our strategy is then extended to simultaneously incorporate mixtures of dyes, whose fluorescence cascade creates <span class="hlt">calcite</span> nanoparticles that fluoresce white. This offers a simple strategy for generating biocompatible and stable fluorescent nanoparticles whose output can be tuned as required. PMID:27857076</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25818510','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25818510"><span>Functionalization of biomineral reinforcement in crustacean cuticle: <span class="hlt">Calcite</span> orientation in the partes incisivae of the mandibles of Porcellio scaber and the supralittoral species Tylos europaeus (Oniscidea, Isopoda).</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Huber, Julia; Griesshaber, Erika; Nindiyasari, Fitriana; Schmahl, Wolfgang W; Ziegler, Andreas</p> <p>2015-05-01</p> <p>In arthropods the cuticle forms an exoskeleton with its physical and chemical properties adapted to functions of distinct skeletal elements. The cuticle of the partes incisivae (PI) in mandibles of terrestrial isopods is a composite of chitin-protein fibrils/fibres and minerals. It consists of an unmineralized tip, a middle region with organic fibrils reinforced mainly with amorphous calcium phosphate and a base region mineralized with amorphous calcium carbonate and <span class="hlt">calcite</span>. In this study we extend our work on the structure and material properties of the incisive cuticle employing electron backscatter diffraction (EBSD), and investigate <span class="hlt">calcite</span> orientation patterns in the PI of two terrestrial isopod species from different habitats. We trace small-scale differences in texture sharpness and <span class="hlt">calcite</span> microstructure, and compare <span class="hlt">calcite</span> organization and orientation patterns in the PI with those in the tergites of the same isopod species. We observe that in the PI <span class="hlt">calcite</span> orientation, the degree of <span class="hlt">crystal</span> alignment, and mode of crystalline domain assemblage is highly varied within short length scales. This contrasts to <span class="hlt">calcite</span> organization in the tergite cuticle, where <span class="hlt">calcite</span> has only one specific texture pattern. Such a large range in the variation of <span class="hlt">calcite</span> organization has not been observed in other carbonate biological hard tissues, such as shells and teeth, where one specific texture and microstructure prevails. Thus, the investigated isopod species are able to control <span class="hlt">crystallization</span> of the amorphous carbonate precursor in a differential way, most probably related to the function of the individual skeletal element and the animals' behavior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015APS..SHK.U2001T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015APS..SHK.U2001T"><span>Anisotropic Transverse Stress in <span class="hlt">Calcite</span> and Sapphire Measured Using Birefringence</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tear, Gareth R.; Chapman, David J.; Eakins, Daniel E.; Proud, William G.</p> <p>2015-06-01</p> <p>Many significant geological minerals have anisotropic <span class="hlt">crystal</span> structures leading to material properties that are anisotropic, including compressive elastic behaviour. A non-invasive approach to investigate the directional dependence of transverse stress in these materials during shock compression would supplement current understanding. As many geological minerals are transparent and hence optically anisotropic, measuring the change in birefringence induced by transverse stress in the material offers the possibility of a fast, non-invasive approach to probe transverse behaviour. Shock compression experiments have been performed on a-cut <span class="hlt">calcite</span> and a-cut sapphire for strain rates of order 105 s-1 and up to longitudinal stresses of 2 GPa for <span class="hlt">calcite</span> and 12 GPa for sapphire. We present measured changes in birefringence for these materials under shock compression, comparing with current and past literature as well as an in house optical model. The authors would like to thank Mr Steve Johnson and Mr David Pittman for technical support. The Institute of Shock Physics acknowledges the continued support of AWE and Imperial College London.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SedG..335...93M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SedG..335...93M"><span>Growing spherulitic <span class="hlt">calcite</span> grains in saline, hyperalkaline lakes: experimental evaluation of the effects of Mg-clays and organic acids</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mercedes-Martín, R.; Rogerson, M. R.; Brasier, A. T.; Vonhof, H. B.; Prior, T. J.; Fellows, S. M.; Reijmer, J. J. G.; Billing, I.; Pedley, H. M.</p> <p>2016-04-01</p> <p>The origin of spherical-radial <span class="hlt">calcite</span> bodies - spherulites - in sublacustrine, hyperalkaline and saline systems is unclear, and therefore their palaeoenvironmental significance as allochems is disputed. Here, we experimentally investigate two hypotheses concerning the origin of spherulites. The first is that spherulites precipitate from solutions super-saturated with respect to magnesium-silicate clays, such as stevensite. The second is that spherulite precipitation happens in the presence of dissolved, organic acid molecules. In both cases, experiments were performed under sterile conditions using large batches of a synthetic and cell-free solution replicating waters found in hyperalkaline, saline lakes (such as Mono Lake, California). Our experimental results show that a highly alkaline and highly saline solution supersaturated with respect to <span class="hlt">calcite</span> (control solution) will precipitate euhedral to subhedral rhombic and trigonal bladed <span class="hlt">calcite</span> <span class="hlt">crystals</span>. The same solution supersaturated with respect to stevensite precipitates sheet-like stevensite <span class="hlt">crystals</span> rather than a gel, and <span class="hlt">calcite</span> precipitation is reduced by ~ 50% compared to the control solution, producing a mixture of patchy prismatic subhedral to euhedral, and minor needle-like, <span class="hlt">calcite</span> <span class="hlt">crystals</span>. Enhanced magnesium concentration in solution is the likely the cause of decreased volumes of <span class="hlt">calcite</span> precipitation, as this raised equilibrium ion activity ratio in the solution. On the other hand, when alginic acid was present then the result was widespread development of micron-size calcium carbonate spherulite bodies. With further growth time, but falling supersaturation, these spherules fused into botryoidal-topped crusts made of micron-size fibro-radial <span class="hlt">calcite</span> <span class="hlt">crystals</span>. We conclude that the simplest tested mechanism to deposit significant spherical-radial <span class="hlt">calcite</span> bodies is to begin with a strongly supersaturated solution that contains specific but environmentally-common organic acids. Furthermore, we found</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_11 --> <div id="page_12" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="221"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22512172','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22512172"><span>[In situ experimental study of phase transition of <span class="hlt">calcite</span> by Raman spectroscopy at high temperature and high pressure].</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Liu, Chuan-jiang; Zheng, Hai-fei</p> <p>2012-02-01</p> <p>The phase transitions of <span class="hlt">calcite</span> at high temperature and high pressure were investigated by using hydrothermal diamond anvil cell combined with Raman spectroscopy. The result showed that the Raman peak of 155 cm(-1) disappeared, the peak of 1 087 cm(-1) splited into 1083 and 1 090 cm(-1) peaks and the peak of 282 cm(-1) abruptly reduced to 231 cm(-1) at ambient temperature when the system pressure increased to 1 666 and 2 127 MPa respectively, which proved that <span class="hlt">calcite</span> transformed to <span class="hlt">calcite</span>-II and <span class="hlt">calcite</span>-III. In the heating process at the initial pressure of 2 761 MPa and below 171 degrees C, there was no change in Raman characteristic peaks of <span class="hlt">calcite</span>-III. As the temperature increased to 171 degrees C, the color of <span class="hlt">calcite</span> <span class="hlt">crystal</span> became opaque completely and the symmetric stretching vibration peak of 1 087 cm(-1), in-plane bending vibration peak of 713 cm(-1) and lattice vibration peaks of 155 and 282 cm(-1) began to mutate, showing that the <span class="hlt">calcite</span>-III transformed to a new phase of calcium carbonate at the moment. When the temperature dropped to room temperature, this new phase remained stable all along. It also indicated that the process of phase transformation from <span class="hlt">calcite</span> to the new phase of calcium carbonate was irreversible. The equation of phase transition between <span class="hlt">calcite</span>-III and new phase of calcium carbonate can be determined by P(MPa) = 9.09T x (degrees C) +1 880. The slopes of the Raman peak (v1 087) of symmetrical stretching vibration depending on pressure and temperature are dv/dP = 5.1 (cm(-1) x GPa(-1)) and dv/dT = -0.055 3(cm(-1) x degrees C(-1)), respectively.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatSR...628854A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatSR...628854A"><span>Modelling how incorporation of divalent cations affects <span class="hlt">calcite</span> wettability–implications for biomineralisation and oil recovery</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Andersson, M. P.; Dideriksen, K.; Sakuma, H.; Stipp, S. L. S.</p> <p>2016-06-01</p> <p>Using density functional theory and geochemical speciation modelling, we predicted how solid-fluid interfacial energy is changed, when divalent cations substitute into a <span class="hlt">calcite</span> surface. The effect on wettability can be dramatic. Trace metal uptake can impact organic compound adsorption, with effects for example, on the ability of organisms to control <span class="hlt">crystal</span> growth and our ability to predict the wettability of pore surfaces. Wettability influences how easily an organic phase can be removed from a surface, either organic compounds from contaminated soil or crude oil from a reservoir. In our simulations, transition metals substituted exothermically into <span class="hlt">calcite</span> and more favourably into sites at the surface than in the bulk, meaning that surface properties are more strongly affected than results from bulk experiments imply. As a result of divalent cation substitution, <span class="hlt">calcite</span>-fluid interfacial energy is significantly altered, enough to change macroscopic contact angle by tens of degrees. Substitution of Sr, Ba and Pb makes surfaces more hydrophobic. With substitution of Mg and the transition metals, <span class="hlt">calcite</span> becomes more hydrophilic, weakening organic compound adsorption. For biomineralisation, this provides a switch for turning on and off the activity of organic <span class="hlt">crystal</span> growth inhibitors, thereby controlling the shape of the associated mineral phase.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4926276','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4926276"><span>Modelling how incorporation of divalent cations affects <span class="hlt">calcite</span> wettability–implications for biomineralisation and oil recovery</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Andersson, M. P.; Dideriksen, K.; Sakuma, H.; Stipp, S. L. S.</p> <p>2016-01-01</p> <p>Using density functional theory and geochemical speciation modelling, we predicted how solid-fluid interfacial energy is changed, when divalent cations substitute into a <span class="hlt">calcite</span> surface. The effect on wettability can be dramatic. Trace metal uptake can impact organic compound adsorption, with effects for example, on the ability of organisms to control <span class="hlt">crystal</span> growth and our ability to predict the wettability of pore surfaces. Wettability influences how easily an organic phase can be removed from a surface, either organic compounds from contaminated soil or crude oil from a reservoir. In our simulations, transition metals substituted exothermically into <span class="hlt">calcite</span> and more favourably into sites at the surface than in the bulk, meaning that surface properties are more strongly affected than results from bulk experiments imply. As a result of divalent cation substitution, <span class="hlt">calcite</span>-fluid interfacial energy is significantly altered, enough to change macroscopic contact angle by tens of degrees. Substitution of Sr, Ba and Pb makes surfaces more hydrophobic. With substitution of Mg and the transition metals, <span class="hlt">calcite</span> becomes more hydrophilic, weakening organic compound adsorption. For biomineralisation, this provides a switch for turning on and off the activity of organic <span class="hlt">crystal</span> growth inhibitors, thereby controlling the shape of the associated mineral phase. PMID:27352933</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=calcite+OR+montmorillonite+OR+kaolinite+OR+gibbsite&id=EJ267543','ERIC'); return false;" href="http://eric.ed.gov/?q=calcite+OR+montmorillonite+OR+kaolinite+OR+gibbsite&id=EJ267543"><span>Cyclic Cratonic Carbonates and Phanerozoic <span class="hlt">Calcite</span> Seas.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Wilkinson, Bruce H.</p> <p>1982-01-01</p> <p>Discusses causes of cyclicity in cratonic carbonate sequences and evidence for and potential significance of postulated primary <span class="hlt">calcite</span> sediment components in past Paleozoic seas, outlining problems, focusing on models explaining existing data, and identifying background. Future sedimentary geologists will need to address these and related areas…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013Nanos...6..852K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013Nanos...6..852K"><span>Bio-inspired formation of functional <span class="hlt">calcite</span>/metal oxide nanoparticle composites</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kim, Yi-Yeoun; Schenk, Anna S.; Walsh, Dominic; Kulak, Alexander N.; Cespedes, Oscar; Meldrum, Fiona C.</p> <p>2013-12-01</p> <p>Biominerals are invariably composite materials, where occlusion of organic macromolecules within single <span class="hlt">crystals</span> can significantly modify their properties. In this article, we take inspiration from this biogenic strategy to generate composite <span class="hlt">crystals</span> in which magnetite (Fe3O4) and zincite (ZnO) nanoparticles are embedded within a <span class="hlt">calcite</span> single <span class="hlt">crystal</span> host, thereby endowing it with new magnetic or optical properties. While growth of <span class="hlt">crystals</span> in the presence of small molecules, macromolecules and particles can lead to their occlusion within the <span class="hlt">crystal</span> host, this approach requires particles with specific surface chemistries. Overcoming this limitation, we here precipitate <span class="hlt">crystals</span> within a nanoparticle-functionalised xyloglucan gel, where gels can also be incorporated within single <span class="hlt">crystals</span>, according to their rigidity. This method is independent of the nanoparticle surface chemistry and as the gel maintains its overall structure when occluded within the <span class="hlt">crystal</span>, the nanoparticles are maintained throughout the <span class="hlt">crystal</span>, preventing, for example, their movement and accumulation at the <span class="hlt">crystal</span> surface during <span class="hlt">crystal</span> growth. This methodology is expected to be quite general, and could be used to endow a wide range of <span class="hlt">crystals</span> with new functionalities.Biominerals are invariably composite materials, where occlusion of organic macromolecules within single <span class="hlt">crystals</span> can significantly modify their properties. In this article, we take inspiration from this biogenic strategy to generate composite <span class="hlt">crystals</span> in which magnetite (Fe3O4) and zincite (ZnO) nanoparticles are embedded within a <span class="hlt">calcite</span> single <span class="hlt">crystal</span> host, thereby endowing it with new magnetic or optical properties. While growth of <span class="hlt">crystals</span> in the presence of small molecules, macromolecules and particles can lead to their occlusion within the <span class="hlt">crystal</span> host, this approach requires particles with specific surface chemistries. Overcoming this limitation, we here precipitate <span class="hlt">crystals</span> within a nanoparticle</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/113821','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/113821"><span>Fluid inclusion studies of <span class="hlt">calcite</span> veins from Yucca Mountain, Nevada, Tuffs: Environment of formation</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Roedder, E.; Whelan, J.F.; Vaniman, D.T.</p> <p>1994-12-31</p> <p><span class="hlt">Calcite</span> vein and vug fillings at four depths (130-314m), all above the present water table in USW G-1 bore hole at Yucca Mountain, Nevada, contain primary fluid inclusions with variable vapor/liquid raitos: Most of these inclusions are either full of liquid or full of vapor. The liquid-filled inclusions show that most of the host <span class="hlt">calcite</span> <span class="hlt">crystallized</span> from fluids at <100{degrees}C. The vapor-filled inclusions provide evidence that a separate vapor phase was present in the fluid during <span class="hlt">crystallization</span>. Studies of these vapor-filled inclusions on the microscope crushing stage were interpreted in an earlier paper as indicating trapping of an air-water-CO{sub 2} vapor phase at ``<100{degrees}C``. Our new studies reveal the additional presence of major methane in the vapor-filled inclusion, indicating even lower temperatures of trapping, perhaps at near-surface temperatures. They also show that the host <span class="hlt">calcite</span> <span class="hlt">crystals</span> grew from a flowing film of water on the walls of fractures open to the atmosphere, the vapor-filled inclusions representing bubbles that exsolved from this film onto the <span class="hlt">crystal</span> surface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002AGUFMOS21B0193S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002AGUFMOS21B0193S"><span>Planktic Foraminiferal Sedimentation and <span class="hlt">Calcite</span> Budget</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schiebel, R.</p> <p>2002-12-01</p> <p>Vertical flux and sedimentation rate of planktic foraminiferal tests is quantified on a global scale. The planktic foraminiferal test flux is a consequence of the population dynamics, and the differential settling modes for different species are a precondition for the differences in the regional flux rates. The average planktic foraminiferal <span class="hlt">calcite</span> flux rate at the 100-m depth-level is estimated at 50% of the global-marine <span class="hlt">calcite</span> flux and 6% of the total carbon flux. The most significant decrease in the planktic foraminiferal test flux rates between 100-700 m water depth possibly results from increased bacterially-mediated decomposition of cytoplasm and a decreasing pH in microenvironments within foraminiferal tests. Throughout most of the year, on average only 1-3% of the initially exported CaCO3 reaches the deep sea floor. Pulsed flux events, mass dumps of fast settling particles, yield a major contribution of tests to the formation of deep-sea sediments. On a global average, ~25% of the total <span class="hlt">calcite</span> produced by planktic foraminifers arrives in the deep ocean and at the sediment surface. To complete the open-marine, particulate CaCO3 inventory, the contribution of coccolithophores, pteropods, and calcareous dinophytes is discussed. The global planktic foraminiferal <span class="hlt">calcite</span> flux rate at 100 m depth amounts to 23-56% of the total open marine CaCO3 flux. The total planktic foraminiferal contribution of CaCO3 to global surface sediments is estimated at 0.36-0.88 Gt per year, ~30-80% of the total deep-marine <span class="hlt">calcite</span> budget.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16190195','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16190195"><span>Inhibition of <span class="hlt">calcite</span> precipitation by natural organic material: kinetics, mechanism, and thermodynamics.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lin, Yi-Pin; Singer, Philip C; Aiken, George R</p> <p>2005-09-01</p> <p>The inhibition of <span class="hlt">calcite</span> precipitation by natural organic material (NOM) in solutions <span class="hlt">seeded</span> with <span class="hlt">calcite</span> was investigated using a pH-stat system. Experiments were carried out using three NOMs with different physical/chemical properties. For each of the materials, inhibition was found to be more effective at lower carbonate/calcium ratios and lower pH values. The reduction in the precipitation rate could be explained by a Langmuir adsorption model using a conditional equilibrium constant. By identification of the type of site on the NOM molecules that is involved in the adsorption reaction, the "conditional" equilibrium constants obtained at different solution compositions converged to a single "nonconditional" value. The thermodynamic data determined at 25 degrees C and 1 atm suggest that the interaction between NOM molecules and the <span class="hlt">calcite</span> surface is chemisorptive in nature and that adsorption is an endothermic reaction driven by the entropy change. The greatest degree of inhibition was observed for the NOM with the highest molecular weight and aromatic carbon content. For a given type of NOM, the degree of inhibition of <span class="hlt">calcite</span> precipitation was dictated bythe balance between the enthalpy change and the entropy change of the adsorption reaction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70027810','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70027810"><span>Inhibition of <span class="hlt">calcite</span> precipitation by natural organic material: Kinetics, mechanism, and thermodynamics</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Lin, Y.-P.; Singer, P.C.; Aiken, G.R.</p> <p>2005-01-01</p> <p>The inhibition of <span class="hlt">calcite</span> precipitation by natural organic material (NOM) in solutions <span class="hlt">seeded</span> with <span class="hlt">calcite</span> was investigated using a pH-stat system. Experiments were carried out using three NOMs with different physical/chemical properties. For each of the materials, inhibition was found to be more effective at lower carbonate/calcium ratios and lower pH values. The reduction in the precipitation rate could be explained by a Langmuir adsorption model using a conditional equilibrium constant. By identification of the type of site on the NOM molecules that is involved in the adsorption reaction, the "conditional" equilibrium constants obtained at different solution compositions converged to a single "nonconditional" value. The thermodynamic data determined at 25??C and 1 atm suggest that the interaction between NOM molecules and the <span class="hlt">calcite</span> surface is chemisorptive in nature and that adsorption is an endothermic reaction driven by the entropy change. The greatest degree of inhibition was observed for the NOM with the highest molecular weight and aromatic carbon content. For a given type of NOM, the degree of inhibition of <span class="hlt">calcite</span> precipitation was dictated by the balance between the enthalpy change and the entropy change of the adsorption reaction. ?? 2005 American Chemical Society.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19800060500&hterms=Cactus&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DCactus','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19800060500&hterms=Cactus&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DCactus"><span>Shock-induced effects in <span class="hlt">calcite</span> from Cactus Crater</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Vizgirda, J.; Ahrens, T. J.; Tsay, F.-D.</p> <p>1980-01-01</p> <p>The paper discusses shock metamorphism of <span class="hlt">calcite</span> from coralline limestone samples retrieved from a borehole drilled into rocks beneath Cactus Crater, a nuclear explosion crater at Eniwetok Atoll. The metamorphism was detected and quantified using electron spin resonance (ESR); the ESR spectra of Mn(+) present as a trace constituent in the coral samples, show a consistent decrease in hyperfine peak splitting with decreasing depth of sample. It is suggested that the decrease in hyperfine peak splitting reflects a decrease in <span class="hlt">crystal</span> field splitting, and therefore, small increases on cation-anion distances produced by mechanical energy input during the shock process. Two alternative crater models suggested by the ESR results are a depiction of a steady decay of the shock wave, and a delineation of a breccia lens with a breccia-bedrock interface at 20 plus or minus 5 m.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3788374','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3788374"><span>Structural evolution of <span class="hlt">calcite</span> at high temperatures: Phase V unveiled</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ishizawa, Nobuo; Setoguchi, Hayato; Yanagisawa, Kazumichi</p> <p>2013-01-01</p> <p>The <span class="hlt">calcite</span> form of calcium carbonate CaCO3 undergoes a reversible phase transition between Rc and Rm at ~1240 K under a CO2 atmosphere of ~0.4 MPa. The joint probability density function obtained from the single-<span class="hlt">crystal</span> X-ray diffraction data revealed that the oxygen triangles of the CO3 group in the high temperature form (Phase V) do not sit still at specified positions in the space group Rm, but migrate along the undulated circular orbital about carbon. The present study also shows how the room temperature form (Phase I) develops into Phase V through an intermediate form (Phase IV) in the temperature range between ~985 K and ~1240 K. PMID:24084871</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70015640','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70015640"><span>Thermodynamics of magnesian <span class="hlt">calcite</span> solid-solutions at 25°C and 1 atm total pressure</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Busenberg, Eurybiades; Plummer, L. Niel</p> <p>1989-01-01</p> <p> protodolomite. Group I and II solid-solutions differ significantly in stability. The rate of <span class="hlt">crystal</span> growth and the chemical composition of the aqueous solutions from which the solids were formed are the main factors controlling stoichiometric solubility of the magnesian <span class="hlt">calcites</span> and the density of <span class="hlt">crystal</span> defects. The literature on the occurrence and behavior of magnesian <span class="hlt">calcites</span> in sea water and other aqueous solutions is also examined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/966152','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/966152"><span>in situ <span class="hlt">Calcite</span> Precipitation for Contaminant Immobilization</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Yoshiko Fujita; Robert W. Smith</p> <p>2009-08-01</p> <p>in situ <span class="hlt">Calcite</span> Precipitation for Contaminant Immobilization Yoshiko Fujita (Yoshiko.fujita@inl.gov) (Idaho National Laboratory, Idaho Falls, Idaho, USA) Robert W. Smith (University of Idaho-Idaho Falls, Idaho Falls, Idaho, USA) Subsurface radionuclide and trace metal contaminants throughout the U.S. Department of Energy (DOE) complex pose one of DOE’s greatest challenges for long-term stewardship. One promising stabilization mechanism for divalent trace ions, such as the short-lived radionuclide strontium-90, is co-precipitation in <span class="hlt">calcite</span>. <span class="hlt">Calcite</span>, a common mineral in the arid western U.S., can form solid solutions with trace metals. The rate of trace metal incorporation is susceptible to manipulation using either abiotic or biotic means. We have previously demonstrated that increasing the <span class="hlt">calcite</span> precipitation rate by stimulating the activity of urea hydrolyzing microorganisms can result in significantly enhanced Sr uptake. Urea hydrolysis causes the acceleration of calcium carbonate precipitation (and trace metal co-precipitation) by increasing pH and alkalinity, and also by liberating the reactive cations from the aquifer matrix via exchange reactions involving the ammonium ion derived from urea: H2NCONH2 + 3H2O ? 2NH4+ + HCO3- + OH- urea hydrolysis >X:2Ca + 2NH4+ ? 2>X:NH4 + Ca2+ ion exchange Ca2+ + HCO3- + OH- ? CaCO3(s) + H2O <span class="hlt">calcite</span> precipitation where >X: is a cation exchange site on the aquifer matrix. This contaminant immobilization approach has several attractive features. Urea hydrolysis is catalyzed by the urease enzyme, which is produced by many indigenous subsurface microorganisms. Addition of foreign microbes is unnecessary. In turn the involvement of the native microbes and the consequent in situ generation of reactive components in the aqueous phase (e.g., carbonate and Ca or Sr) can allow dissemination of the reaction over a larger volume and/or farther away from an amendment injection point, as compared to direct addition of the reactants at</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1213531','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1213531"><span>Kinetics and Mechanisms of <span class="hlt">Calcite</span> Reactions with Saline Waters</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Gorman, Brian P</p> <p>2015-09-02</p> <p>Project Description: The general objective of the proposed research is to determine the kinetics and mechanisms of <span class="hlt">calcite</span> reactions with saline waters over a wide range of saline water composition, pCO<sub>2</sub>, and modest ranges in T and P. This will be accomplished by studying both reaction rates and solubility from changes in solution chemistry, and making nanoscale observations of <span class="hlt">calcite</span> precipitate surface morphology and composition at the micro-to-nano-scale to provide an understanding of controlling reaction mechanisms and pathways. The specific objectives necessary to reach the general objective are: a) determination of how pCO<sub>2</sub>, Ca<sup>2+</sup>, ionic strength and “foreign” ions influence reaction rates; and b) investigate the influence of these parameters on apparent kinetic solubility from dissolution and precipitation reactions. This information will clearly be central to the construction of reliable reaction-transport models to predict reservoir and formation response to increased CO<sub>2</sub> in saline waters. This program was initially collaborative with John Morse at Texas A&M, however his passing shortly after the beginning of this program resulted in abbreviated research time and effort. Summary of Results: Early studies using electron microscopy and spectroscopy indicated that carbonate precipitation from natural seawater (NSW) conditions onto aragonite substrates was mediated by a surface amorphous calcium carbonate layer. It was hypothesized that this ACC layer (observed after < 5days reaction time) was responsible for the abnormal reaction kinetics and also served as a metastable <span class="hlt">seed</span> layer for growth of epitaxial aragonite. Further studies of the ACC formation mechanism indicated a strong dependence on the Mg concentration in solution. Subsequent studies at shorter times (10 hrs) on <span class="hlt">calcite</span> substrates and in a wide range of supersaturation conditions did not indicate any ACC layer. Instead, an epitaxial layer by layer</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26177610','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26177610"><span>Deformation twinning and the role of amino acids and magnesium in <span class="hlt">calcite</span> hardness from molecular simulation.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Côté, A S; Darkins, R; Duffy, D M</p> <p>2015-08-21</p> <p>We employ classical molecular dynamics to calculate elastic properties and to model the nucleation and propagation of deformation twins in <span class="hlt">calcite</span>, both as a pure <span class="hlt">crystal</span> and with magnesium and aspartate inclusions. The twinning is induced by applying uniaxial strain to the <span class="hlt">crystal</span> and relaxing all stress components except the uniaxial component. A detailed analysis of the atomistic processes reveal that the twinning mechanism involves small displacements of the Ca ions and cooperative rotations of the CO3 ions. The volume of the twinned region expands under increased uniaxial strain via the propagation of steps along the twin boundaries. The energy cost of the twin boundaries is compensated by the reduced hydrostatic stress and strain energy. The presence of biogenic impurities is shown to decrease the strain required to induce twin formation in <span class="hlt">calcite</span> and, thus, the yield stress. This increased propensity for twinning provides a possible explanation for the increased hardness and penetration resistance observed experimentally in biominerals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.B41B0038T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.B41B0038T"><span>Dissolution Kinetics of Biogenic Magnesian <span class="hlt">Calcites</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Thompson, R.; Guidry, M.; Mackenzie, F. T.; De Carlo, E. H.</p> <p>2014-12-01</p> <p>Ocean acidification (OA) is a serious concern for the health of calcifying ecosystems in the near future. During the past century, surface ocean pH has decreased by ~0.1 pH units, and is expected to decrease further by 0.3-0.4 pH units by the end of this century. The process of OA will likely result in both decreased calcification rates and increased rates of carbonate mineral dissolution, particularly involving the magnesian <span class="hlt">calcite</span> (Mg-<span class="hlt">calcite</span>) calcifiers found in shallow-water reef and other carbonate environments. Many Mg-<span class="hlt">calcite</span> compositions are the most soluble of the carbonate phases commonly found in reef environments (often comprising much of the cementation and structure within a reef), and are therefore potentially the most susceptible to dissolution processes associated with OA. However, the dissolution kinetics of these phases is poorly known, limiting our ability to understand their behavior in nature. Laboratory experiments designed to investigate the mechanisms and dissolution rates of biogenic Mg-<span class="hlt">calcite</span> mineral phases in distilled water and seawater over a range of CO2 and T conditions were conducted employing both batch and fluidized-bed reactor systems and using a variety of cleaned and annealed biogenic Mg-<span class="hlt">calcite</span> phases. Our initial results have shown that the dissolution rate at 298 K and a pCO2 of ~350 ppm of the crustose coralline alga Amphiroa rigida (~20 mol% MgCO3) in seawater undersaturated with respect to this phase is 3.6 μmol g-1 hr-1, nearly 50% greater than that under similar conditions for aragonite. This rate and the derived experimental rate law are consistent with the preliminary findings of Walter and Morse (1985). Additional kinetic (and also solubility) data will be presented for the following species: Chiton tuberculatus (~0-4 mol% MgCO3); Echinometra mathei and/or Lytechinus variegatus (~8-12 mol% MgCO3); Homotrema rubrum (12-16 mol% MgCO3); and Lithothamnion sp. (~18-24 mol% MgCO3). Quantification of the rates of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26669167','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26669167"><span>[Study on Mineralogical Characteristics of Quartz and <span class="hlt">Calcite</span> from Feieling Skarn-Type Pb-Zn Deposit in Southwest Margin of Yunkai Massif].</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zeng, Chang-yu; Zhao, Ming-zhen; Li, Hong-zhong; Niu, Jia; Zhang, Jie-tang; He, Jun-guo; Zhou, Yong-zhang; Yang, Zhi-jun</p> <p>2015-09-01</p> <p>The Feieling Pb-Zn deposit of skarn-type is located the in Southwest margin of Yunkai massif, China. This ore deposit can be divided into wall rock near ore, concealed rock mass, endoskarn, exoskarn and orebody. The Raman and FTIR spectrum are conducted to study the mineralogical characteristics of quartz and <span class="hlt">calcite</span> from five types of rocks from Feieling skarn-type deposit. The analysis shows that the quartz included in the near ore wall rock, endoskarn and exoskarn, comparing with recrystallized quartz of concealed rock mass, has a tend to change into low symmetry quartz in varying degrees. The crystalinity and order degree of quartz from near ore wall rock to concealed rock mass and to endoskarn are becoming higher, but that of quartz from different exoskarn samples display no regular. The origin or the quartz microstructure changes may be related to the multi-stage evolution of skarn mineralization process. The quartz, included in near ore wall rock, endoskarn and exoskarn, become easier to recrystallize and adjust microstructure under the influence of the multi-stage hydrothermal and temperature effect. In anyone sample, the earlier crystalline <span class="hlt">calcite</span>, showing subhedral-euhedral <span class="hlt">crystal</span>, display higher crystalinity and order degree. On the contrary, the later crystalline <span class="hlt">calcite</span>, showing xenomorphic <span class="hlt">crystal</span>, display lower crystalinity and order degree. <span class="hlt">Calcite</span> <span class="hlt">crystal</span> of exoskarn rock contains some silica impurity, while endoskarn and orebody rock is pure. The purity of <span class="hlt">calcite</span> <span class="hlt">crystal</span> may relate to Multi-stage evolution of skarn mineralization process. At the early and late skarn stage, active silica-containing fluid is easier to join into <span class="hlt">calcite</span>, which is under higher temperature environments. On the contrary, at the late quartz-surfide stage, the later <span class="hlt">crystalized</span> <span class="hlt">calcite</span> displays higher purity, which is under lower temperature environments. Therefore, spectral characteristics of quartz and <span class="hlt">calcite</span> reflect multi-stage evolution of skarn mineralization</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012JCrGr.352..151R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012JCrGr.352..151R"><span><span class="hlt">Calcite</span> growth-rate inhibition by fulvic acid and magnesium ion—Possible influence on biogenic <span class="hlt">calcite</span> formation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Reddy, Michael M.</p> <p>2012-08-01</p> <p>Increases in ocean surface water dissolved carbon dioxide (CO2) concentrations retard biocalcification by reducing <span class="hlt">calcite</span> supersaturation (Ωc). Reduced calcification rates may influence growth-rate dependent magnesium ion (Mg) incorporation into biogenic <span class="hlt">calcite</span> modifying the use of calcifying organisms as paleoclimate proxies. Fulvic acid (FA) at biocalcification sites may further reduce calcification rates. <span class="hlt">Calcite</span> growth-rate inhibition by FA and Mg, two common constituents of seawater and soil water involved in the formation of biogenic <span class="hlt">calcite</span>, was measured separately and in combination under identical, highly reproducible experimental conditions. <span class="hlt">Calcite</span> growth rates (pH=8.5 and Ωc=4.5) are reduced by FA (0.5 mg/L) to 47% and by Mg (10-4 M) to 38%, compared to control experiments containing no added growth-rate inhibitor. Humic acid (HA) is twice as effective a <span class="hlt">calcite</span> growth-rate inhibitor as FA. <span class="hlt">Calcite</span> growth rate in the presence of both FA (0.5 mg/L) and Mg (10-4 M) is reduced to 5% of the control rate. Mg inhibits <span class="hlt">calcite</span> growth rates by substitution for calcium ion at the growth site. In contrast, FA inhibits <span class="hlt">calcite</span> growth rates by binding multiple carboxylate groups on the <span class="hlt">calcite</span> surface. FA and Mg together have an increased affinity for the <span class="hlt">calcite</span> growth sites reducing <span class="hlt">calcite</span> growth rates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70042984','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70042984"><span><span class="hlt">Calcite</span> growth-rate inhibition by fulvic acid and magnesium ion—Possible influence on biogenic <span class="hlt">calcite</span> formation</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Reddy, Michael M.</p> <p>2012-01-01</p> <p>Increases in ocean surface water dissolved carbon dioxide (CO2) concentrations retard biocalcification by reducing <span class="hlt">calcite</span> supersaturation (Ωc). Reduced calcification rates may influence growth-rate dependent magnesium ion (Mg) incorporation into biogenic <span class="hlt">calcite</span> modifying the use of calcifying organisms as paleoclimate proxies. Fulvic acid (FA) at biocalcification sites may further reduce calcification rates. <span class="hlt">Calcite</span> growth-rate inhibition by FA and Mg, two common constituents of seawater and soil water involved in the formation of biogenic <span class="hlt">calcite</span>, was measured separately and in combination under identical, highly reproducible experimental conditions. <span class="hlt">Calcite</span> growth rates (pH=8.5 and Ωc=4.5) are reduced by FA (0.5 mg/L) to 47% and by Mg (10−4 M) to 38%, compared to control experiments containing no added growth-rate inhibitor. Humic acid (HA) is twice as effective a <span class="hlt">calcite</span> growth-rate inhibitor as FA. <span class="hlt">Calcite</span> growth rate in the presence of both FA (0.5 mg/L) and Mg (10−4 M) is reduced to 5% of the control rate. Mg inhibits <span class="hlt">calcite</span> growth rates by substitution for calcium ion at the growth site. In contrast, FA inhibits <span class="hlt">calcite</span> growth rates by binding multiple carboxylate groups on the <span class="hlt">calcite</span> surface. FA and Mg together have an increased affinity for the <span class="hlt">calcite</span> growth sites reducing <span class="hlt">calcite</span> growth rates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21473269','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21473269"><span>Magnesian <span class="hlt">calcite</span> sorbent for carbon dioxide capture.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Mabry, James C; Mondal, Kanchan</p> <p>2011-01-01</p> <p>Magnesian <span class="hlt">calcite</span> with controlled properties was synthesized for the removal of carbon dioxide. The results from characterization, reactivity and CO2 capture capacity for different synthesis conditions are reported. The magnesian <span class="hlt">calcite</span> samples (CaCO3:MgCO3) were synthesized by the coprecipitation of specific amounts of commercially available CaO and MgO by carbon dioxide. Characterization was done with BET, SEM/EDS, particle size analysis and XRD. The capacity was measured using TGA cycles at 800 degrees C and compared for different preparation conditions. The effects of CaO, MgO and surfactant loading on the physical properties and carbonation activity were studied to determine the optimal synthesis condition. A long-term carbonation-calcination cycling test was conducted on the optimal sample. It was observed that the sample maintained its capacity to 86% of its original uptake even after 50 cycles.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_12 --> <div id="page_13" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="241"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11453695','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11453695"><span><span class="hlt">Crystal</span> structure of native and Cd/Cd-substituted Dioclea guianensis <span class="hlt">seed</span> lectin. A novel manganese-binding site and structural basis of dimer-tetramer association.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wah, D A; Romero, A; Gallego del Sol, F; Cavada, B S; Ramos, M V; Grangeiro, T B; Sampaio, A H; Calvete, J J</p> <p>2001-07-20</p> <p>Diocleinae legume lectins are a group of oligomeric proteins whose subunits display a high degree of primary structure and tertiary fold conservation but exhibit considerable diversity in their oligomerisation modes. To elucidate the structural determinants underlaying Diocleinae lectin oligomerisation, we have determined the <span class="hlt">crystal</span> structures of native and cadmium-substituted Dioclea guianensis (Dguia) <span class="hlt">seed</span> lectin. These structures have been solved by molecular replacement using concanavalin (ConA) coordinates as the starting model, and refined against data to 2.0 A resolution. In the native (Mn/Ca-Dguia) <span class="hlt">crystal</span> form (P4(3)2(1)2), the asymmetric unit contains two monomers arranged into a canonical legume lectin dimer, and the tetramer is formed with a symmetry-related dimer. In the Cd/Cd-substituted form (I4(1)22), the asymmetric unit is occupied by a monomer. In both <span class="hlt">crystal</span> forms, the tetrameric association is achieved by the corresponding symmetry operators. Like other legume lectins, native D. guianensis lectin contains manganese and calcium ions bound in the vicinity of the saccharide-combining site. The architecture of these metal-binding sites (S1 and S2) changed only slightly in the cadmium/cadmium-substituted form. A highly ordered calcium (native lectin) or cadmium (Cd/Cd-substituted lectin) ion is coordinated at the interface between dimers that are not tetrameric partners in a similar manner as the previously identified Cd(2+) in site S3 of a Cd/Ca-ConA. An additional Mn(2+) coordination site (called S5), whose presence has not been reported in <span class="hlt">crystal</span> structures of any other homologous lectin, is present in both, the Mn/Ca and the Cd/Cd-substituted D. guianensis lectin forms. On the other hand, comparison of the primary and quaternary <span class="hlt">crystal</span> structures of <span class="hlt">seed</span> lectins from D. guianensis and Dioclea grandiflora (1DGL) indicates that the loop comprising residues 117-123 is ordered to make interdimer contacts in the D. grandiflora lectin structure</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JGRB..120.6614G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JGRB..120.6614G"><span>Frictional behavior of talc-<span class="hlt">calcite</span> mixtures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Giorgetti, C.; Carpenter, B. M.; Collettini, C.</p> <p>2015-09-01</p> <p>Faults involving phyllosilicates appear weak when compared to the laboratory-derived strength of most crustal rocks. Among phyllosilicates, talc, with very low friction, is one of the weakest minerals involved in various tectonic settings. As the presence of talc has been recently documented in carbonate faults, we performed laboratory friction experiments to better constrain how various amounts of talc could alter these fault's frictional properties. We used a biaxial apparatus to systematically shear different mixtures of talc and <span class="hlt">calcite</span> as powdered gouge at room temperature, normal stresses up to 50 MPa and under different pore fluid saturated conditions, i.e., CaCO3-equilibrated water and silicone oil. We performed slide-hold-slide tests, 1-3000 s, to measure the amount of frictional healing and velocity-stepping tests, 0.1-1000 µm/s, to evaluate frictional stability. We then analyzed microstructures developed during our experiments. Our results show that with the addition of 20% talc the <span class="hlt">calcite</span> gouge undergoes a 70% reduction in steady state frictional strength, a complete reduction of frictional healing and a transition from velocity-weakening to velocity-strengthening behavior. Microstructural analysis shows that with increasing talc content, deformation mechanisms evolve from distributed cataclastic flow of the granular <span class="hlt">calcite</span> to localized sliding along talc-rich shear planes, resulting in a fully interconnected network of talc lamellae from 20% talc onward. Our observations indicate that in faults where talc and <span class="hlt">calcite</span> are present, a low concentration of talc is enough to strongly modify the gouge's frictional properties and specifically to weaken the fault, reduce its ability to sustain future stress drops, and stabilize slip.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18284149','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18284149"><span>Neptunium(V) coprecipitation with <span class="hlt">calcite</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Heberling, Frank; Denecke, Melissa A; Bosbach, Dirk</p> <p>2008-01-15</p> <p>Coprecipitation experiments of Np(V) and U(VI) with <span class="hlt">calcite</span> were performed in mixed-flow reactors under steady state conditions at room temperature for up to 400 h at precipitation rates of 1.0 x 10(-8) to 6.8 x 10(-8) mol/(m2 s). The saturation index with respect to <span class="hlt">calcite</span> varied between 0.04 and 0.95. Initial Np(V) or U(VI) concentrations were 1 micromol/L, 0.01 mol/L NaCl was used as background electrolyte, and pH ranged from 7.8 to 12.8. Partition coefficients for Np(V) were in the range of 0.5-10.3, compared to 0.02 for U(VI). Np L(III) and U L(III) EXAFS were used to characterize the local structural environment of the incorporated actinides. In the case of U(VI), the structural environment is not unambiguously characterized. Our data suggest that Np(V) ions occupy calcium lattice sites. The two axial oxygen atoms of the linear neptunyl moiety substitute two <span class="hlt">calcite</span> carbonate groups in the first coordination sphere. Thus, four carbonate groups coordinate the neptunyl-ion in a monodentate fashion with four equatorial oxygen atoms (Oeq) at 2.4 A and associated carbon atoms (C) at 3.2 A. The interatomic distances indicate slight structural relaxation of the carbonate groups from their ideal sites. A similar structural model has been reported for U(VI) incorporated into natural <span class="hlt">calcite</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26457519','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26457519"><span><span class="hlt">Crystallization</span> and preliminary X-ray diffraction studies of frutalin, an α-D-galactose-specific lectin from Artocarpus incisa <span class="hlt">seeds</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Monteiro-Moreira, Ana Cristina de Oliveira; D'Muniz Pereira, Humberto; Vieira Neto, Antonio Eufrasio; Mendes Batista Moreno, Frederico Bruno; Duarte Pinto Lobo, Marina; de Sousa, Felipe Domingos; Moreira, Renato de Azevedo</p> <p>2015-10-01</p> <p>Frutalin is an α-D-galactose-specific carbohydrate-binding glycoprotein with antitumour properties and is a powerful tool for tumour biomarker discovery. The <span class="hlt">crystallization</span> and preliminary X-ray diffraction analysis of this lectin, which was isolated from Artocarpus incisa <span class="hlt">seeds</span>, are reported here. Frutalin was purified and submitted to mass-spectrometric analysis. Diverse masses at approximately 16 kDa were observed in the deconvoluted spectra, which support the presence of isoforms. The best frutalin <span class="hlt">crystals</span> were grown within a week in 0.1 M citric acid pH 3.5 which contained 25% PEG 3350 as a precipitant at 293 K, and diffracted to a maximum resolution of 1.81 Å. The monoclinic <span class="hlt">crystals</span> belonged to space group I2, with unit-cell parameters a = 76.17, b = 74.56, c = 118.98 Å, β = 96.56°. A molecular-replacement solution was obtained which indicated the presence of four monomers per asymmetric unit. Crystallographic refinement of the structure is in progress.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ApPhA.122..613L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ApPhA.122..613L"><span>Progress of p-channel bottom-gate poly-Si thin-film transistor by nickel silicide <span class="hlt">seed</span>-induced lateral <span class="hlt">crystallization</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Sol Kyu; Seok, Ki Hwan; Park, Jae Hyo; Kim, Hyung Yoon; Chae, Hee Jae; Jang, Gil Su; Lee, Yong Hee; Han, Ji Su; Joo, Seung Ki</p> <p>2016-06-01</p> <p>Excimer laser annealing (ELA) is known to be the most common <span class="hlt">crystallization</span> technology for the fabrication of low-temperature polycrystalline-silicon (poly-Si) thin-film transistors (TFTs) in the mass production industry. This technology, however, cannot be applied to bottom-gate (BG) TFTs, which are well developed for the liquid-<span class="hlt">crystal</span> display (LCD) back-planes, because strong laser energy of ELA can seriously damage the other layers. Here, we propose a novel high-performance BG poly-Si TFT using Ni silicide <span class="hlt">seed</span>-induced lateral <span class="hlt">crystallization</span> (SILC). The SILC technology renders it possible to ensure low damage in the layers, smooth surface, and longitudinal large grains in the channel. It was observed that the electrical properties exhibited a steep subthreshold slope of 110 mV/dec, high field-effect mobility of 304 cm2/Vsec, high I on/ I off ratio of 5.9 × 107, and a low threshold voltage of -3.9 V.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1810896S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1810896S"><span>Microstructural analysis of <span class="hlt">calcite</span>-filled fractures inherited from basement structures, southern Ontario, Canada: long term instability of the craton?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Spalding, Jennifer; Schneider, David</p> <p>2016-04-01</p> <p>Intra-cratonic regions are generally characterized by tectonic stability and low seismicity. In southern Ontario, Canada, moderate levels of seismicity have been recorded over the last few decades reaching magnitudes of 5 MN, indicating that the geosphere is not as stable as predicted. The stratigraphy of the region consists of Ordovician limestone with a thickness of ~200 m that unconformably overlays the Mesoproterozoic crystalline Grenville Province. Subsequent tectonism including repeated Paleozoic orogenies and rifting along the east coast of North America has reactivated Proterozoic structures that have propagated into the overlying carbonate platform forming mesoscopic-scale brittle structures. Exposed along the shores of Lake Ontario are decameter-scale fracture zones, with a fracture spacing of 0.5 to 10 meters. The dominant fracture set trends E-W, and often forms conjugate sets with less prominent NNE-oriented fractures. More locally, an older NW-oriented fracture set is cross cut by the E-W and NNE oriented fractures. Regionally, there have been six directions of maximum horizontal stress in southern Ontario since the Precambrian, with the current orientation of maximum stress oriented ENE as a consequence of far field Atlantic ridge-push forces generated at distant plate boundaries. <span class="hlt">Calcite</span> mineralization along fractured surfaces locally form sub-horizontal slickenside fabrics which are covered by a layer of euhedral <span class="hlt">calcite</span> <span class="hlt">crystals</span>, suggesting that fracture dilation (and fluid flow) occurred after fracture slip to allow the growth of <span class="hlt">calcite</span> <span class="hlt">crystals</span>. Due to the proximity of the carbonate units to the crystalline basement, we expect the <span class="hlt">calcitic</span> veins to be enriched in rare earth elements and are presently conducting geochemical analyses. The <span class="hlt">calcite</span> veins and surfaces vary from 2.5 cm to 1 mm thicknesses, often with larger <span class="hlt">calcite</span> <span class="hlt">crystals</span> in the center of the vein and smaller <span class="hlt">crystals</span> at the vein boundaries, likely representing nucleation on small</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/929930','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/929930"><span>Arsenate Uptake by <span class="hlt">Calcite</span>: Macroscopic and Spectroscopic Characterization of Adsorption and Incorporation Mechanisms</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Alexandratos,V.; Elzinga, E.; Reeder, R.</p> <p>2007-01-01</p> <p>Batch uptake experiments and X-ray element mapping and spectroscopic techniques were used to investigate As(V) (arsenate) uptake mechanisms by <span class="hlt">calcite</span>, including adsorption and coprecipitation. Batch sorption experiments in <span class="hlt">calcite</span>-equilibrated suspensions (pH 8.3; PCO{sub 2} = 10{sup -3.5} atm) reveal rapid initial sorption to <span class="hlt">calcite</span>, with sorption rate gradually decreasing with time as available sorption sites decrease. An As(V)-<span class="hlt">calcite</span> sorption isotherm determined after 24 h equilibration exhibits Langmuir-like behavior up to As concentrations of 300 {mu}M. Maximum distribution coefficient values (K{sub d}), derived from a best fit to a Langmuir model, are {approx}190 L kg{sup -1}. <span class="hlt">Calcite</span> single <span class="hlt">crystals</span> grown in the presence of As(V) show well-developed rhombohedral morphology with characteristic growth hillocks on (10{bar 1}4) surfaces at low As(V) concentrations ({<=}5 {mu}M), but habit modification is evident at As(V) concentrations {>=}30 {mu}M in the form of macrostep development preferentially on the - vicinal surfaces of growth hillocks. Micro-X-ray fluorescence element mapping of (10{bar 1}4) surfaces shows preferential incorporation of As in the - vicinal faces relative to + vicinals. EXAFS fit results for both adsorption and coprecipitation samples confirm that As occurs in the 5+ oxidation state in tetrahedral coordination with oxygen, i.e., as arsenate. For adsorption samples, As(V) forms inner-sphere surface complexes via corner-sharing with Ca octahedra. As(V) coprecipitated with <span class="hlt">calcite</span> substitutes in carbonate sites but with As off-centered, as indicated by two Ca shells, and with likely disruption of local structure. The results indicate that As(V) interacts strongly with the <span class="hlt">calcite</span> surface, similar to often-cited analog phosphate, and uptake can occur via both adsorption and coprecipitation reactions. Therefore, <span class="hlt">calcite</span> may be effective for partial removal of dissolved arsenate from aquatic and soil systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JCrGr.450..148N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JCrGr.450..148N"><span>Heterogeneous growth of <span class="hlt">calcite</span> at aragonite {001}- and vaterite {001}-melt interfaces: A molecular dynamics simulation study</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nada, Hiroki; Nishimura, Tatsuya; Sakamoto, Takeshi; Kato, Takashi</p> <p>2016-09-01</p> <p><span class="hlt">Crystal</span> growth at the interface between a calcium carbonate (CaCO3) <span class="hlt">crystal</span> and its melt at a high temperature of 1500 K is investigated by means of a molecular dynamics simulation. The simulation is performed for the interfaces of a <span class="hlt">calcite</span> {104} plane, aragonite {001}, {100}, and {010} planes, and vaterite {001}, {110}, and {100} planes. The growth from a pure melt and that from a melt containing Mg2+ are examined. <span class="hlt">Calcite</span> growth occurs on the <span class="hlt">calcite</span> {104} plane, aragonite growth occurs on the aragonite {100}, and {010} planes, and vaterite growth occurs on the vaterite {110} and {100} planes. However, the heterogeneous growth of <span class="hlt">calcite</span> occurs on the {001} plane of aragonite and vaterite, irrespective of the presence of Mg2+. The results advance our understanding of geological processes that occur at high temperature, such as the formation of CaCO3 <span class="hlt">crystals</span> from carbonatite magma and the formation of marble. Moreover, the results provide useful information for the control of CaCO3 <span class="hlt">crystal</span> formation in material design.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22642750','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22642750"><span>Atomistic simulations of calcium uranyl(VI) carbonate adsorption on <span class="hlt">calcite</span> and stepped-<span class="hlt">calcite</span> surfaces.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Doudou, Slimane; Vaughan, David J; Livens, Francis R; Burton, Neil A</p> <p>2012-07-17</p> <p>Adsorption of actinyl ions onto mineral surfaces is one of the main mechanisms that control the migration of these ions in environmental systems. Here, we present computational classical molecular dynamics (MD) simulations to investigate the behavior of U(VI) in contact with different <span class="hlt">calcite</span> surfaces. The calcium-uranyl-carbonate [Ca(2)UO(2)(CO(3))(3)] species is shown to display both inner- and outer-sphere adsorption to the flat {101̅4} and the stepped {314̅8} and {31̅2̅16} planes of <span class="hlt">calcite</span>. Free energy calculations, using the umbrella sampling method, are employed to simulate adsorption paths of the same uranyl species on the different <span class="hlt">calcite</span> surfaces under aqueous condition. Outer-sphere adsorption is found to dominate over inner-sphere adsorption because of the high free energy barrier of removing a uranyl-carbonate interaction and replacing it with a new uranyl-surface interaction. An important binding mode is proposed involving a single vicinal water monolayer between the surface and the sorbed complex. From the free energy profiles of the different <span class="hlt">calcite</span> surfaces, the uranyl complex was also found to adsorb preferentially on the acute-stepped {314̅8} face of <span class="hlt">calcite</span>, in agreement with experiment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeCoA.134..221X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeCoA.134..221X"><span>Kinetics and mechanisms of cadmium carbonate heteroepitaxial growth at the <span class="hlt">calcite</span> (10 1bar 4) surface</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xu, Man; Kovarik, Libor; Arey, Bruce W.; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien</p> <p>2014-06-01</p> <p>Elucidating the kinetics and mechanisms of heteroepitaxial nucleation and growth at mineral-water interfaces is essential to understanding surface reactivity in geochemical systems. In the present work, the formation of heteroepitaxial cadmium carbonate coatings at <span class="hlt">calcite</span>-water interfaces was investigated by exposing <span class="hlt">calcite</span> (10 1bar 4) surfaces to Cd-bearing aqueous solutions. In situ atomic force microscopy (AFM) was employed as the primary technique. The AFM results indicate that the heteroepitaxial growth of cadmium carbonate proceeds via three different mechanisms depending on the initial supersaturation of the aqueous solution: advancement of existing steps, nucleation and growth of three-dimensional (3D) islands, and nucleation and spread of two-dimensional (2D) nuclei. The 3D islands and 2D nuclei exhibit different morphologies and growth kinetics. The effects of supersaturation on heteroepitaxial growth mechanisms can be interpreted in terms of the free energy barrier for nucleation. At low initial supersaturation, where 3D nucleation dominates, it is hypothesized, from the growth rate and morphology of the 3D islands observed with AFM, that the <span class="hlt">crystallization</span> of the overgrowth follows a non-classical pathway involving the formation of a surface precursor that is not fully crystalline, whereas high supersaturation favors the formation of crystalline 2D nuclei whose morphology is based on the atomic structure of the <span class="hlt">calcite</span> substrate. Cross-sectional transmission electron microscopy (TEM) images reveal that the atomic structure of the interface between the cadmium carbonate coating and <span class="hlt">calcite</span> shows perfect, dislocation-free epitaxy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1130243','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1130243"><span>Kinetics and Mechanisms of Cadmium Carbonate Heteroepitaxial Growth at the <span class="hlt">Calcite</span> (101¯4) Surface</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Xu, Man; Kovarik, Libor; Arey, Bruce W.; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien N.</p> <p>2014-06-01</p> <p>Elucidating the kinetics and mechanisms of heteroepitaxial nucleation and growth at mineral-water interfaces is essential to understanding surface reactivity in geochemical systems. In the present work, the formation of heteroepitaxial cadmium carbonate coatings at <span class="hlt">calcite</span>-water interfaces was investigated by exposing <span class="hlt">calcite</span> (10-14) surfaces to Cd-bearing aqueous solutions. In situ atomic force microscopy (AFM) was employed as the primary technique. The AFM results indicate that the heteroepitaxial growth of cadmium carbonate proceeds via three different mechanisms depending on the initial supersaturation of the aqueous solution: advancement of existing steps, nucleation and growth of three-dimensional (3D) islands, and nucleation and spread of two-dimensional (2D) nuclei. The 3D islands and 2D nuclei exhibit different morphologies and growth kinetics. The effects of supersaturation on heteroepitaxial growth mechanisms can be interpreted in terms of the free energy barrier for nucleation. At low initial supersaturation, where 3D nucleation dominates, it is hypothesized, from the growth rate and morphology of the 3D islands observed with AFM, that the <span class="hlt">crystallization</span> of the overgrowth follows a non-classical pathway involving the formation of a surface precursor that is not fully crystalline, whereas high supersaturation favors the formation of crystalline 2D nuclei whose morphology is based on the atomic structure of the <span class="hlt">calcite</span> substrate. Cross-sectional transmission electron microscopy (TEM) images reveal that the atomic structure of the interface between the cadmium carbonate coating and <span class="hlt">calcite</span> shows perfect, dislocation-free epitaxy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20020024136&hterms=growth+characterization&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dgrowth%2Bcharacterization','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20020024136&hterms=growth+characterization&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dgrowth%2Bcharacterization"><span>Characterization and In-Situ Monitoring of ZnSe <span class="hlt">Crystal</span> Growth by <span class="hlt">Seeded</span> PVT for Microgravity Applications</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Feth, Shari T.</p> <p>2001-01-01</p> <p><span class="hlt">Crystal</span> growth from the vapor phase continues to play a significant role in the production of II-VI semiconductor compounds (ZnO, ZnTe, CdTe, etc.) and SiC. As compared to melt growth methods (where available) the advantages are: (1) lower growth temperature(s); (2) reduction in defect concentration; (3) additional purification; and (4) enhanced <span class="hlt">crystal</span> perfection. A powerful tool in determining the mechanism of PVT is microgravity. Under normal gravity conditions the transport mechanism is a superposition of diffusive and convective fluxes. Microgravity offers the possibility of studying the transport properties without the influence of convective effects. Research on the <span class="hlt">crystal</span> growth of ZnSe by PVT (P.I.: Su of NASA/MSFC) will help to clarify the effects of convection on <span class="hlt">crystal</span> growth. A <span class="hlt">crystal</span> growth furnace with in-situ and real time optical monitoring capabilities was constructed and used to monitor the vapor composition and growing <span class="hlt">crystal</span> surface morphology during the PVT growth of ZnSe. Using photoluminescence and SIMS, ex-situ, the incorporation of point defects (Zn vacancy) and impurities was found to be correlated to the gravity vector due to the influence of the convective flow. A summary of the results to date will be presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70024665','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70024665"><span>Physical and stable-isotope evidence for formation of secondary <span class="hlt">calcite</span> and silica in the unsaturated zone, Yucca Mountain, Nevada</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Whelan, J.F.; Paces, J.B.; Peterman, Z.E.</p> <p>2002-01-01</p> <p><span class="hlt">Calcite</span> and silica form coatings on fracture footwalls and cavity floors in the welded tuffs at Yucca Mountain, the potential site of a high-level radioactive waste repository. These secondary mineral deposits are heterogeneously distributed in the unsaturated zone (UZ) with fewer than 10% of possible depositional sites mineralized. The paragenetic sequence, compiled from deposits throughout the UZ, consists of an early-stage assemblage of <span class="hlt">calcite</span>??fluorite??zeolites that is frequently capped by chalcedony??quartz. Intermediate- and late-stage deposits consist largely of <span class="hlt">calcite</span>, commonly with opal on buried growth layers or outermost <span class="hlt">crystal</span> faces of the <span class="hlt">calcite</span>. Coatings on steep-dipping fractures usually are thin (??? 3 mm) with low-relief outer surfaces whereas shallow-dipping fractures and lithophysal cavities typically contain thicker, more coarsely crystalline deposits characterized by unusual thin, tabular <span class="hlt">calcite</span> blades up to several cms in length. These blades may be capped with knobby or corniced overgrowths of late-stage <span class="hlt">calcite</span> intergrown with opal. The observed textures in the fracture and cavity deposits are consistent with deposition from films of water fingering down fracture footwalls or drawn up faces of growing <span class="hlt">crystals</span> by surface tension and evaporated at the <span class="hlt">crystal</span> tips. Fluid inclusion studies have shown that most early-stage and some intermediate-stage <span class="hlt">calcite</span> formed at temperatures of 35 to 85??C. <span class="hlt">Calcite</span> deposition during the past several million years appears to have been at temperatures < 30??C. The elevated temperatures indicated by the fluid inclusions are consistent with temperatures estimated from <span class="hlt">calcite</span> ??18O values. Although others have interpreted the elevated temperatures as evidence of hydrothermal activity and flooding of the tuffs of the potential repository, the authors conclude that the temperatures and fluid-inclusion assemblages are consistent with deposition in a UZ environment that experienced prolonged heat input from</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3541355','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3541355"><span>Selectively increasing of polyunsaturated (18:2) and monounsaturated (18:1) fatty acids in Jatropha curcas <span class="hlt">seed</span> oil by <span class="hlt">crystallization</span> using D-optimal design</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p></p> <p>2012-01-01</p> <p>Background This study was done to obtain concentrated polyunsaturated fatty acid (PUFA) linoleic acid (LA; 18:2) and monounsaturated fatty acid (MUFA) oleic acid (OA; 18:1) from Jatropha curcas <span class="hlt">seed</span> oil by urea complexation. Urea complexation is a method used by researchers to separate fatty acids (FAs) based on their molecular structure. Effects the ratio of urea-to-FAs, <span class="hlt">crystallization</span> temperature and <span class="hlt">crystallization</span> time on the final products of urea complexation were examined. D-optimal Design was employed to study the significance of these factors and the optimum conditions for the technique were predicted and verified. Results Optimum conditions of the experiment to obtain maximum concentration of LA were predicted at urea-to-FAs ratio (w/w) of 5:1, <span class="hlt">crystallization</span> temperature of −10°C and 24 h of <span class="hlt">crystallization</span> time. Under these conditions, the final non-urea complex fraction (NUCF) was predicted to contain 92.81% of LA with the NUCF yield of 7.8%. The highest percentage of OA (56.01%) was observed for samples treated with 3:1 urea-to-FAs ratio (w/w) at 10°C for 16 h. The lowest percentage of LA (8.13%) was incorporated into urea complex fraction (UCF) with 1:1 urea-to-FAs ratio (w/w) at 10°C for 8 h. Conclusions The separation of PUFA (LA) and MUFA (OA) described here. Experimental variables should be carefully controlled in order to recover a maximum content of PUFA and MUFA of interest with reasonable yield% with a desirable purity of fatty acid of interest. PMID:22747574</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25790337','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25790337"><span>Adsorption of ethanol and water on <span class="hlt">calcite</span>: dependence on surface geometry and effect on surface behavior.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Keller, K S; Olsson, M H M; Yang, M; Stipp, S L S</p> <p>2015-04-07</p> <p>Molecular dynamics (MD) simulations were used to explore adsorption on <span class="hlt">calcite</span>, from a 1:1 mixture of ethanol and water, on planar {10.4} and stepped, i.e. vicinal, surfaces. Varying the surface geometry resulted in different adsorption patterns, which would directly influence the ability of ethanol to control <span class="hlt">calcite</span> <span class="hlt">crystal</span> growth, dissolution, and adsorption/desorption of other ions and molecules. Ethanol forms a well-ordered adsorbed layer on planar faces and on larger terraces, such as between steps and defects, providing little chance for water, with its weaker attachment, to displace it. However, on surfaces with steps, adsorption affinity depends on the length of the terraces between the steps. Long terraces allow ethanol to form a well-ordered, hydrophobic layer, but when step density is high, ethanol adsorption is less ordered, allowing water to associate at and near the steps and even displacing pre-existing ethanol. Water adsorbed at steps forms mass transport pathways between the bulk solution and the solid surface. Our simulations confirm the growth inhibiting properties of ethanol, also explaining how certain <span class="hlt">crystal</span> faces are more stabilized because of their surface geometry. The -O(H) functional group on ethanol forms tight bonds with <span class="hlt">calcite</span>; the nonpolar, -CH3 ends, which point away from the surface, create a hydrophobic layer that changes surface charge, thus wettability, and partly protects <span class="hlt">calcite</span> from precipitation and dissolution. These tricks could easily be adopted by biomineralizing organisms, allowing them to turn on and off <span class="hlt">crystal</span> growth. They undoubtedly also play a role in the wetting properties of mineral surfaces in commercial CaCO3 manufacture, oil production, and contamination remediation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6855095','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6855095"><span>Biological control of <span class="hlt">crystal</span> texture: A widespread strategy for adapting <span class="hlt">crystal</span> properties to function</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Berman, A.; Leiserowitz, L.; Weiner, S.; Addadi, L. ); Hanson, J.; Koetzle, T.F. )</p> <p>1993-02-05</p> <p>Textures of <span class="hlt">calcite</span> <span class="hlt">crystals</span> from a variety of mineralized tissues belong to organisms from four phyla were examined with high-resolution synchrotron x-ray radiation. Significant differences in coherence length and angular spread were observed between taxonomic groups. <span class="hlt">Crystals</span> from polycrystalline skeletal ensembles were more perfect than those that function as single-<span class="hlt">crystal</span> elements. Different anistropic effects on <span class="hlt">crystal</span> texture were observed for sea urchin and mollusk <span class="hlt">calcite</span> <span class="hlt">crystals</span>, whereas none was found for the foraminifer, Patellina, and the control <span class="hlt">calcite</span> <span class="hlt">crystals</span>. These results show that the manipulation of <span class="hlt">crystal</span> texture in different organisms is under biological control and that <span class="hlt">crystal</span> textures in some tissues are adapted to function. A better understanding of this apparently widespread biological phenomenon may provide new insights for improving synthetic <span class="hlt">crystal</span>-containing materials. 18 refs., 3 figs., 1 tab.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1168889','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1168889"><span>Tuning <span class="hlt">calcite</span> morphology and growth acceleration by a rational design of highly stable protein-mimetics</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Chen, Chunlong; Qi, Jiahui; Tao, Jinhui; Zuckermann, Ronald; De Yoreo, James J.</p> <p>2014-09-05</p> <p>In nature, proteins play a significant role in biomineral formation. One of the ultimate goals of bioinspired materials science is to develop highly stable synthetic molecules that mimic the function of these natural proteins by controlling <span class="hlt">crystal</span> formation. Here, we demonstrate that both the morphology and the degree of acceleration or inhibition observed during growth of <span class="hlt">calcite</span> in the presence of peptoids can be rationally tuned by balancing the electrostatic interactions (EI) and hydrophobic interactions (HI), with HI playing the dominant role. While either strong EI or HI inhibit growth and suppress (104) face expression, correlations between peptoid-<span class="hlt">crystal</span> binding energies and observed changes in <span class="hlt">calcite</span> growth indicate moderate EI allow peptoids to weakly adsorb while moderate HI cause disruption of surface-adsorbed water layers, leading to growth acceleration with retained expression of (104) faces. This study provides fundamental principles for designing peptoids as <span class="hlt">crystallization</span> promoters, and offers a straightforward screening method based on macroscopic <span class="hlt">crystal</span> morphology. Because peptoids are sequence-specific, highly stable, and easily synthesized, peptoid-enhanced <span class="hlt">crystallization</span> offers a broad range of potential applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1995Metic..30R.550M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1995Metic..30R.550M"><span>New Shocked <span class="hlt">Calcite</span> and Fe Grains from Noerdlingen Ries Impact Crater</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miura, Y.</p> <p>1995-09-01</p> <p>Shocked minerals with simple chemical composition of silica, carbon or iron material reveal high-pressure phase during compression process [1]. As <span class="hlt">calcite</span> mineral shows high-pressure phase of aragonite it should have the "shocked phase" formed from high-pressure phase mixed with quenched materials of gas-melt reaction [2,3,4]. The main purposes of this paper are (1) to discuss new shocked materials of <span class="hlt">calcite</span> found in the Noerdlingen Ries impact crater. Germany and artificial impact phases. and (2) to show new findings of fine Fe-grains and anomalous plagioclase in suevite. Single grains of anomalous <span class="hlt">calcite</span> for X-ray analysis were selected from limestone with wormy or bubble-included texture in Buschelberg Ries impact crater (sample R8) [3 4]. Powdered and single grain samples of anomalous <span class="hlt">calcites</span> show low X-ray intensity and high Bragg angle shift. compared with standard <span class="hlt">calcite</span> of Akiyoshi limestone as listed in Table 1 [2.3.4]. The unit-cell dimensions of the single grain measured with the four-axes X-ray diffractometer in Yamaguchi University were determined by the least square calculation from the "highest X-ray intensity peak" of each <span class="hlt">crystal</span> plane which is the same data of the powdered X-ray diffraction sample as an average structure . Both powdered and single grain data reveal high density of 2.76 g/cm^3 (between aragonite of density: rho=2.8g/cm^3, and normal <span class="hlt">calcite</span>: rho=2.71g/cm^3) of the <span class="hlt">calcite</span> cell which is the same characters of shocked phases of quartz or graphite [1,2,3,4] (Table 1). Anomalous <span class="hlt">calcite</span> contains minor amount of Si Fe Ti, though major cation is Ca of 99.4% in cation content. These foreign elements are mixed with during the formation in vapor plume [5]. Table 1, showing the x-ray density and unit-cell parameters of anomalous shocked <span class="hlt">calcite</span> with high density from Ries and artificial impact craters, appears here in the hard copy. Two types of shocked <span class="hlt">calcites</span> are found in artificial impact experiments of railgun of the ISAS. Japan. (a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012GeCoA..89..226B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012GeCoA..89..226B"><span>Removal of organic magnesium in coccolithophore <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Blanco-Ameijeiras, S.; Lebrato, M.; Stoll, H. M.; Iglesias-Rodriguez, M. D.; Méndez-Vicente, A.; Sett, S.; Müller, M. N.; Oschlies, A.; Schulz, K. G.</p> <p>2012-07-01</p> <p>Coccolithophore <span class="hlt">calcite</span> refers to the plates of calcium carbonate (CaCO3) produced by the calcifying phytoplankton, coccolithophores. The empirical study of the elemental composition has a great potential in the development of paleoproxies. However, the difficulties to separate coccolithophore carbonates from organic phases hamper the investigation of coccoliths magnesium to calcium ratios (Mg/Ca) in biogeochemical studies. Magnesium (Mg) is found in organic molecules in the cells at concentrations up to 400 times higher than in inorganically precipitated <span class="hlt">calcite</span> in present-day seawater. The aim of this study was to optimize a reliable procedure for organic Mg removal from coccolithophore samples to ensure reproducibility in measurements of inorganic Mg in <span class="hlt">calcite</span>. Two baseline methods comprising organic matter oxidations with (1) bleach and (2) hydrogen peroxide (H2O2) were tested on synthetic pellets, prepared by mixing reagent grade CaCO3 with organic matter from the non-calcifying marine algae Chlorella autotrophica and measured with an ICP-AES (inductively coupled plasma-atomic emission spectrometer). Our results show that treatments with a reductive solution [using hydroxylamine-hydrochloride (NH2OH·HCl + NH4OH)] followed by three consecutive oxidations (using H2O2) yielded the best cleaning efficiencies, removing >99% of organic Mg in 24 h. P/Ca and Fe/Ca were used as indicators for organic contamination in the treated material. The optimized protocol was tested in dried coccolithophore pellets from batch cultures of Emiliania huxleyi, Calcidiscus leptoporus and Gephyrocapsa oceanica. Mg/Ca of treated coccolithophores were 0.151 ± 0.018, 0.220 ± 0.040, and 0.064 ± 0.023 mmol/mol, respectively. Comparison with Mg/Ca literature coccolith values, suggests a tight dependence on modern seawater Mg/Ca, which changes as a consequence of different seawater origins (<10%). The reliable determination of Mg/Ca and Sr/Ca, and the low levels of organic contamination</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5343501','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5343501"><span>The origin of carbon isotope vital effects in coccolith <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>McClelland, H. L. O.; Bruggeman, J.; Hermoso, M.; Rickaby, R. E. M.</p> <p>2017-01-01</p> <p><span class="hlt">Calcite</span> microfossils are widely used to study climate and oceanography in Earth's geological past. Coccoliths, readily preserved <span class="hlt">calcite</span> plates produced by a group of single-celled surface-ocean dwelling algae called coccolithophores, have formed a significant fraction of marine sediments since the Late Triassic. However, unlike the shells of foraminifera, their zooplankton counterparts, coccoliths remain underused in palaeo-reconstructions. Precipitated in an intracellular chemical and isotopic microenvironment, coccolith <span class="hlt">calcite</span> exhibits large and enigmatic departures from the isotopic composition of abiogenic <span class="hlt">calcite</span>, known as vital effects. Here we show that the calcification to carbon fixation ratio determines whether coccolith <span class="hlt">calcite</span> is isotopically heavier or lighter than abiogenic <span class="hlt">calcite</span>, and that the size of the deviation is determined by the degree of carbon utilization. We discuss the theoretical potential for, and current limitations of, coccolith-based CO2 paleobarometry, that may eventually facilitate use of the ubiquitous and geologically extensive sedimentary archive. PMID:28262764</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_13 --> <div id="page_14" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="261"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017NatCo...814511M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017NatCo...814511M"><span>The origin of carbon isotope vital effects in coccolith <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McClelland, H. L. O.; Bruggeman, J.; Hermoso, M.; Rickaby, R. E. M.</p> <p>2017-03-01</p> <p><span class="hlt">Calcite</span> microfossils are widely used to study climate and oceanography in Earth's geological past. Coccoliths, readily preserved <span class="hlt">calcite</span> plates produced by a group of single-celled surface-ocean dwelling algae called coccolithophores, have formed a significant fraction of marine sediments since the Late Triassic. However, unlike the shells of foraminifera, their zooplankton counterparts, coccoliths remain underused in palaeo-reconstructions. Precipitated in an intracellular chemical and isotopic microenvironment, coccolith <span class="hlt">calcite</span> exhibits large and enigmatic departures from the isotopic composition of abiogenic <span class="hlt">calcite</span>, known as vital effects. Here we show that the calcification to carbon fixation ratio determines whether coccolith <span class="hlt">calcite</span> is isotopically heavier or lighter than abiogenic <span class="hlt">calcite</span>, and that the size of the deviation is determined by the degree of carbon utilization. We discuss the theoretical potential for, and current limitations of, coccolith-based CO2 paleobarometry, that may eventually facilitate use of the ubiquitous and geologically extensive sedimentary archive.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2040018','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2040018"><span>The effect of preincubation of <span class="hlt">seed</span> <span class="hlt">crystals</span> of uric acid and monosodium urate with undiluted human urine to induce precipitation of calcium oxalate in vitro : implications for urinary stone formation.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Grover, Phulwinder K.; Ryall, Rosemary L.</p> <p>2002-01-01</p> <p>BACKGROUND: Previous studies demonstrated that <span class="hlt">crystals</span> of uric acid (UA) and sodium urate (NaU) can induce the precipitation of calcium oxalate (CaOx) from its inorganic metastable solutions, but similar effects have not been unequivocally shown to occur in urine. The aim of this investigation was to determine whether preincubation of these <span class="hlt">seeds</span> with urine alter their ability to induce deposition of CaOx from solution and thus provide a possible explanation for discrepancy of results obtained from aqueous inorganic solutions and undiluted urine. MATERIALS AND METHODS: The effects of commercial <span class="hlt">seed</span> <span class="hlt">crystals</span> of UA, NaU and CaOx (6 mg/100 ml) on CaOx <span class="hlt">crystallization</span> were compared in a solution with the same <span class="hlt">crystals</span> that had been preincubated for 3 hours with healthy male urine. A Coulter Counter was used to follow the <span class="hlt">crystallization</span> and decrease in soluble (14) C-oxalate was measured to determine the deposition of CaOx. The precipitated particles were examined by scanning electron microscopy (SEM). The preincubated <span class="hlt">seeds</span> were demineralized and proteins released were analyzed by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE). RESULTS: Analysis of (14) C-oxalate data revealed that while treated UA <span class="hlt">seeds</span> did not affect CaOx deposition, those of NaU and CaOx inhibited the process by 51.9 (p<0.05) and 8.5% (p<0.05) relative to their respective untreated counterparts. Particle size analysis showed that the average modal sizes of particles precipitated in the presence of treated <span class="hlt">seed</span> <span class="hlt">crystals</span> of UA, NaU, and CaOx were very similar to those deposited in the presence of their respective untreated controls. These findings were confirmed by SEM which also showed that <span class="hlt">seed</span> <span class="hlt">crystals</span> of UA and NaU, untreated and treated, were attached like barnacles upon the surfaces of CaOx <span class="hlt">crystals</span> which themselves were bigger than those precipitated in the presence of CaOx <span class="hlt">seeds</span>. SDS-PAGE analysis of the demineralized treated <span class="hlt">seeds</span> showed that they all selectively</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1616010W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1616010W"><span>Impact of trace metals on the water structure at the <span class="hlt">calcite</span> surface</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wolthers, Mariette; Di Tommaso, Devis; De Leeuw, Nora</p> <p>2014-05-01</p> <p>Carbonate minerals play an important role in regulating the chemistry of aquatic environments, including the oceans, aquifers, hydrothermal systems, soils and sediments. Through mineral surface processes such as dissolution, precipitation and sorption, carbonate minerals affect the biogeochemical cycles of not only the constituent elements of carbonates, such as Ca, Mg, Fe and C, but also H, P and trace elements. Surface charging of the <span class="hlt">calcite</span> mineral-water interface, and its reactivity towards foreign ions can be quantified using a surface structural model that includes, among others, the water structure at the interface (i.e. hydrogen bridging) [1,2] in accordance with the CD-MUSIC formalism [3]. Here we will show the impact of foreign metals such as Mg and Sr on the water structure around different surface sites present in etch pits and on growth terraces at the <span class="hlt">calcite</span> (10-14) surface. We have performed Molecular Dynamics simulations of metal-doped <span class="hlt">calcite</span> surfaces, using different interatomic water potentials. Results show that the local environment around the structurally distinct sites differs depending on metal presence, suggesting that metal substitutions in <span class="hlt">calcite</span> affect its reactivity. The information obtained in this study will help in improving existing macroscopic surface model for the reactivity of <span class="hlt">calcite</span> [2] and give more general insight in mineral surface reactivity in relation to <span class="hlt">crystal</span> composition. [1] Wolthers, Charlet, & Van Cappellen (2008). Am. J. Sci., 308, 905-941. [2] Wolthers, Di Tommaso, Du, & de Leeuw (2012). Phys. Chem. Chem. Phys. 14, 15145-15157. [3] Hiemstra and Van Riemsdijk (1996) J. Colloid Interf. Sci. 179, 488-508.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4507537','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4507537"><span>Biomineralization processes of <span class="hlt">calcite</span> induced by bacteria isolated from marine sediments</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Wei, Shiping; Cui, Hongpeng; Jiang, Zhenglong; Liu, Hao; He, Hao; Fang, Nianqiao</p> <p>2015-01-01</p> <p>Biomineralization is a known natural phenomenon associated with a wide range of bacterial species. Bacterial-induced calcium carbonate precipitation by marine isolates was investigated in this study. Three genera of ureolytic bacteria, Sporosarcina sp., Bacillus sp. and Brevundimonas sp. were observed to precipitate calcium carbonate minerals. Of these species, Sporosarcina sp. dominated the cultured isolates. B. lentus CP28 generated higher urease activity and facilitated more efficient precipitation of calcium carbonate at 3.24 ± 0.25 × 10−4 mg/cell. X-ray diffraction indicated that the dominant calcium carbonate phase was <span class="hlt">calcite</span>. Scanning electron microscopy showed that morphologies of the minerals were dominated by cubic, rhombic and polygonal plate-like <span class="hlt">crystals</span>. The dynamic process of microbial calcium carbonate precipitation revealed that B. lentus CP28 precipitated <span class="hlt">calcite</span> <span class="hlt">crystals</span> through the enzymatic hydrolysis of urea, and that when ammonium ion concentrations reached 746 mM and the pH reached 9.6, that favored <span class="hlt">calcite</span> precipitation at a higher level of 96 mg/L. The results of this research provide evidence that a variety of marine bacteria can induce calcium carbonate precipitation, and may influence the marine carbonate cycle in natural environments. PMID:26273260</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26273260','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26273260"><span>Biomineralization processes of <span class="hlt">calcite</span> induced by bacteria isolated from marine sediments.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wei, Shiping; Cui, Hongpeng; Jiang, Zhenglong; Liu, Hao; He, Hao; Fang, Nianqiao</p> <p>2015-06-01</p> <p>Biomineralization is a known natural phenomenon associated with a wide range of bacterial species. Bacterial-induced calcium carbonate precipitation by marine isolates was investigated in this study. Three genera of ureolytic bacteria, Sporosarcina sp., Bacillus sp. and Brevundimonas sp. were observed to precipitate calcium carbonate minerals. Of these species, Sporosarcina sp. dominated the cultured isolates. B. lentus CP28 generated higher urease activity and facilitated more efficient precipitation of calcium carbonate at 3.24 ± 0.25 × 10(-4) mg/cell. X-ray diffraction indicated that the dominant calcium carbonate phase was <span class="hlt">calcite</span>. Scanning electron microscopy showed that morphologies of the minerals were dominated by cubic, rhombic and polygonal plate-like <span class="hlt">crystals</span>. The dynamic process of microbial calcium carbonate precipitation revealed that B. lentus CP28 precipitated <span class="hlt">calcite</span> <span class="hlt">crystals</span> through the enzymatic hydrolysis of urea, and that when ammonium ion concentrations reached 746 mM and the pH reached 9.6, that favored <span class="hlt">calcite</span> precipitation at a higher level of 96 mg/L. The results of this research provide evidence that a variety of marine bacteria can induce calcium carbonate precipitation, and may influence the marine carbonate cycle in natural environments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1007564','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1007564"><span>Basal slip and texture development in <span class="hlt">calcite</span>: new results from torsion experiments</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Barber, D. J.; Wenk, H.-R.; Gomez-Barreiro, J.; Rybacki, E.; Dresen, G.</p> <p>2008-06-09</p> <p>The deformation behavior of <span class="hlt">calcite</span> has been of longstanding interest. Through experiments on single <span class="hlt">crystals</span>, deformation mechanisms were established such as mechanical twinning on e = {l_brace}{bar 1}018{r_brace} <40{bar 4}1> in the positive sense and slip on r = {l_brace}10{bar 1}4{r_brace} <20{bar 2}{bar 1}> and f = {l_brace}{bar 1}012{r_brace} <0{bar 2}2{bar 1}> both in the negative sense. More recently it was observed that at higher temperatures f{l_brace}{bar 1}012{r_brace} <10{bar 1}1> slip in both senses becomes active and, based on slip line analysis, it was suggested that e(0001) <11{bar 2}0> slip may occur. So far there had been no direct evidence for basal slip, which is the dominant system in dolomite. With new torsion experiments on <span class="hlt">calcite</span> single <span class="hlt">crystals</span> at 900 K and transmission electron microscopy, this study identifies (0001) <11{bar 2}0> slip unambiguously by direct imaging of dislocations and diffraction contrast analysis. Including this slip system in polycrystal plasticity simulations, enigmatic texture patterns observed in compression and torsion of <span class="hlt">calcite</span> rocks at high temperature can now be explained, resolving a long-standing puzzle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SedG..345..103J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SedG..345..103J"><span>Mineralogical, crystallographic, and isotopic constraints on the precipitation of aragonite and <span class="hlt">calcite</span> at Shiqiang and other hot springs in Yunnan Province, China</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jones, Brian; Peng, Xiaotong</p> <p>2016-11-01</p> <p>Two active spring vent pools at Shiqiang (Yunnan Province, China) are characterized by a complex array of precipitates that coat the wall around the pool and the narrow ledges that surround the vent pool. These precipitates include arrays of aragonite <span class="hlt">crystals</span>, <span class="hlt">calcite</span> cone-dendrites, red spar <span class="hlt">calcite</span>, unattached dodecahedral and rhombohedral <span class="hlt">calcite</span> <span class="hlt">crystals</span>, and late stage <span class="hlt">calcite</span> that commonly coats and disguises the earlier formed precipitates. Some of the microbial mats that grow on the ledges around the pools have been partly mineralized by microspheres that are formed of Si and minor amounts of Fe. The <span class="hlt">calcite</span> and aragonite that are interspersed with each other at all scales are both primary precipitates. Some laminae, for example, change laterally from aragonite to <span class="hlt">calcite</span> over distances of only a few millimetres. The precipitates at Shiqiang are similar to precipitates found in and around the vent pools of other springs found in Yunnan Province, including those at Gongxiaoshe, Zhuyuan, Eryuan, and Jifei. In all cases, the δDwater and δ18Owater indicate that the spring water is of meteoric origin. These are thermogene springs with the carrier CO2 being derived largely from the mantle and reaction of the waters with bedrock. Variations in the δ13Ctravertine values indicate that the waters in these springs were mixed, to varying degrees, with cold groundwater and its soil-derived CO2. <span class="hlt">Calcite</span> and aragonite precipitation took place once the spring waters had become supersaturated with respect to CaCO3, probably as a result of rapid CO2 degassing. These precipitates, which were not in isotopic equilibrium with the spring water, are characterized by their unusual <span class="hlt">crystal</span> morphologies. The precipitation of <span class="hlt">calcite</span> and aragonite, seemingly together, can probably be attributed to microscale variations in the saturation levels that are, in turn, attributable to microscale variations in the rate of CO2 degassing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1817032W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1817032W"><span>Cyclic growth and branching phenomena of <span class="hlt">calcite</span> grown in Mg(2+) containing solutions and in natural systems</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wiethoff, Felix; Richter, Detlef K.; Neuser, Rolf D.; Immenhauser, Adrian; Gies, Hermann; Schreuer, Jürgen</p> <p>2016-04-01</p> <p>Undulosity in <span class="hlt">calcites</span> (radiaxial fibrous <span class="hlt">calcite</span> (RFC) and fascicular-optic fibrous <span class="hlt">calcite</span> (FOFC)) is a common phenomenon in paleozoic and mesozoic limestones. Despite their importance as archives for climate reconstruction the underlying mechanisms and processes of their formation are still poorly understood [1]. To improve the application of such archives for climate reconstruction a better knowledge of their formation and possible alteration scenarios is necessary. In Mg2+ containing gel based growth experiments <span class="hlt">calcite</span> <span class="hlt">crystals</span> develop pathological morphologies. The morphology can be described as a product of a geometrical selective branching process at the rhombohedral <span class="hlt">crystal</span> faces. Multiple sheet like building blocks evolve at the branching <span class="hlt">crystal</span> face; each slightly tilted in respect to their substrate. The product is a <span class="hlt">crystal</span> aggregate consisting out of several misoriented sub domains. In polarized light thin section microscopy the extinction behaviour of these sub units resemble the optical undulosity of radiaxial fibrous cements. In a multi method approach the local Mg2+ concentration was measured using EMPA and compared with maps of the local <span class="hlt">crystal</span> orientation (via electron backscatter diffraction (EBSD)) and thin section microscopy. We found that Mg2+ is enriched at the sub-domain boundaries and deduced that lattice misfit as a consequence of impurity incorporation causes the <span class="hlt">crystal</span> branching. We propose that this process is cyclic and each new misoriented sheet represents a growth period after a phase of inhibited growth caused by <span class="hlt">crystal</span> faces covered by Mg2+-ions. In comparison to natural systems we found that radiaxial-fibrous cave cements show a pathological morphology based on the same formation principles. [1] Richter et al. (2011) Sediment. Geol. 239, 23-36 [2] Reeder & Paquette (1989) Sediment. Geol. 65, 239-247 [3] Davis et al. (2004) Am. Min. 89, 714-720</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.A23B1257H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.A23B1257H"><span>Cloud Condensation Nucleus Activity of <span class="hlt">calcite</span> and <span class="hlt">calcite</span> coated with model humic and fulvic acids</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hatch, C. D.; Gierlus, K. M.; Schuttlefield, J. D.; Grassian, V. H.</p> <p>2007-12-01</p> <p>Many recent studies have shown that organics can alter the water adsorption and cloud condensation nuclei (CCN) activity of common deliquescent species in the Earth's atmosphere. However, very little is known about the effect of organics on water adsorption and CCN activity of common inactive cloud nuclei, such as mineral aerosol. As many studies have shown that a large fraction of unidentified organic material in aerosol particles is composed of polycarboxylic acids resembling humic substances, the presence of these large molecular weight Humic-Like Substances (HULIS) may also alter the water adsorption and CCN activity of mineral aerosol. Thus, we have measured the water adsorption and CCN activity of model humic and fulvic acids. Additionally, the water adsorption and CCN activity of mineral aerosol particles coated with humic and fulvic acids have been studied. We find that humic and fulvic acids show continual multilayer water adsorption as the relative humidity is raised. Additionally, we find that <span class="hlt">calcite</span> particles mixed with humic and fulvic acids take up more water by mass, by a factor of two, compared to the uncoated <span class="hlt">calcite</span> particles at approximately 70% RH. CCN measurements also indicate that internally mixed <span class="hlt">calcite</span>-humic or fulvic acid aerosols are more CCN active than the otherwise inactive, uncoated <span class="hlt">calcite</span> particles. Our results suggest that mineral aerosol particles coated with high molecular weight organic materials will take up more water and become more efficient CCN in the Earth's atmosphere than single-component mineral aerosol.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6118159','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6118159"><span>Fibrous <span class="hlt">calcite</span> from the Middle Ordovician Holston Formation (east Tennessee)</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Tobin, K.J.; Walker, K.R. . Dept. of Geological Sciences)</p> <p>1993-03-01</p> <p>Fibrous <span class="hlt">calcite</span> from buildups, which occur near the top of the Middle Ordovician Holston Formation, were examined from two localities near Knoxville, TN (Alcoa Highway and Deanne Quarry). Buildups at these localities were deposited under open-marine conditions, slightly down-slope from the platform edge. Fibrous <span class="hlt">calcite</span> (mainly radiaxial fibrous) occur most commonly as cements in mainly stromatactis structures present in bioherms and intergranular porosity in beds that flank bioherms. Fibrous <span class="hlt">calcite</span> is interpreted to have been precipitated in a marine setting. Fibrous <span class="hlt">calcite</span> is uniformly turbid or banded with interlayered turbid and clearer cement. Fibrous <span class="hlt">calcite</span> most commonly shows patchy or blotchy dull-non-luminescence under cathodoluminescence. Bands of uniformly non-luminescent and relatively bright luminescent <span class="hlt">calcite</span> are present. [delta][sup 13]C compositions of fibrous <span class="hlt">calcite</span> vary little (0.6 to 1.0%) but [delta][sup 18]O values are highly variable ([minus]4.8 to [minus]7.1%). Post-marine cement consists of ferroan and non-ferroan, dull luminescent equant <span class="hlt">calcite</span> ([delta][sup 13]C = 0.3 to 0.8; [delta][sup 18]O = [minus]8.6 to [minus]11.5) and is interpreted as precipitated in a deep meteoric or burial setting. Depleted [delta][sup 18]O compositions of fibrous <span class="hlt">calcite</span> reflect addition of post-depositional <span class="hlt">calcite</span> during stabilization. Most enriched [delta][sup 13]C and [delta][sup 18]O fibrous <span class="hlt">calcite</span> composition are similar to enriched values from other Middle Ordovician southern Appalachian buildups (other localities of Holston (TN) and Effna (VA) formations) ([delta][sup 13]C = 0.3 to 0.8; [delta][sup 18]O = [minus]3.9 to [minus]4.8) and may reflect fibrous <span class="hlt">calcite</span> precipitated in isotopic equilibrium with Middle Ordovician sea water.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14..582K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14..582K"><span>Carbonates in thrust faults: High temperature investigations into deformation processes in <span class="hlt">calcite</span>-dolomite systems</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kushnir, A.; Kennedy, L.; Misra, S.; Benson, P.</p> <p>2012-04-01</p> <p>The role of dolomite on the strength and evolution of <span class="hlt">calcite</span>-dolomite fold and thrust belts and nappes (as observed in the Canadian Rockies, the Swiss Alps, the Italian Apennines, and the Naukluft Nappe Complex) is largely unknown. Field investigations indicate that strain in natural systems is localized in <span class="hlt">calcite</span>, resulting in a ductile response, while dolomite deforms in a dominantly brittle manner. To date, experimental studies on polymineralic carbonate systems are limited to homogeneous, fine-grained, <span class="hlt">calcite</span>-dolomite composites of relatively low dolomite content. The effect of dolomite on limestone rheology, the onset of <span class="hlt">crystal</span>-plastic deformation in dolomite in composites, and the potential for strain localization in composites have not yet been fully quantified. Constant displacement rate (3x10-4 s-1and 10-4 s-1), high confining pressure (300 MPa) and high temperature (750° C and 800° C) torsion experiments were conducted to address the role of dolomite on the strength of <span class="hlt">calcite</span>-dolomite composites. Experiments were performed on samples produced by hot isostatic pressing (HIP) amalgams of a natural, pure dolomite and a reagent, pure <span class="hlt">calcite</span>. We performed experiments on the following mixtures (given as dolomite%): 25%, 35%, 50%, and 75%. These synthetic HIP products eliminated concerns of mineralogical impurities and textural anomalies due to porosity, structural fabrics (e.g., foliation) and fossil content. The samples were deformed up to a maximum finite shear strain of 5.0 and the experimental set up was unvented to inhibit sample decarbonation. Mechanical data shows a considerable increase in sample yield strength with increasing dolomite content. Experimental products with low starting dolomite content (dol%: 25% and 35%) display macroscopic strain localization along compositionally defined foliation. Experimental products with high dolomite content (dol%: 50% and 75%) demonstrate no macroscopic foliation. Post-deformation microstructure analysis</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AcSpA..68..656G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AcSpA..68..656G"><span>Spectroscopic characterization of natural <span class="hlt">calcite</span> minerals</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gunasekaran, S.; Anbalagan, G.</p> <p>2007-11-01</p> <p>The FT-IR, FT-Raman, NMR spectral data of ten different limestone samples have been compared. FT-IR and FT-Raman spectral data show that calcium carbonate in limestone, principally in the form of <span class="hlt">calcite</span>, as identified by its main absorption bands at 1426, 1092, 876 and 712 cm -1. The sharp diffractions at the d-spacings, 3.0348, 1.9166 and 1.8796 confirm the presence of <span class="hlt">calcite</span> structure and the calculated lattice parameters are: a = 4.9781 Å, c = 17.1188 Å. The range of 13C chemical shifts for different limestone samples is very small, varying from 198.38 to 198.42 ppm. The observed chemical shifts are consistent with the identical C-O bonding in different limestone samples. 27Al MAS NMR spectra of the samples exhibit a central line at 1 ppm and another line at 60 ppm corresponding to octahedral and tetrahedral Al ions, respectively. The five component resonances were observed in 29Si MAS NMR spectrum of limestone and these resonances were assigned to Si (4 Al), Si (3 Al), Si (2 Al), Si (1 Al) and Si (0 Al) from low field to high field.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006DPS....38.6106S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006DPS....38.6106S"><span>Search For Past Life On Mars: Physical And Chemical Characterization Of <span class="hlt">Calcite</span> Minerals Of Biotic And Abiotic Origin</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stalport, Fabien; Coll, P.; Cabane, M.; Person, A.; Navarro-Gonzales, R.; Raulin, F.; Valay, M.; Ausset, P.; Szopa, C.; McKay, C. P.</p> <p>2006-09-01</p> <p>Several lines of evidence suggest that early Mars once had liquid water on its surface, a denser atmosphere and a mild climate. Similar environmental conditions led to the origin of life on the Earth more than 3.5 billion years ago; consequently, life might also have originated on Mars. We contend that inorganic compounds could give us interesting clues as to the existence of possible biological activity in future astrobiological missions to Mars. Consequently, we have investigated the physical and chemical properties of <span class="hlt">calcite</span>, which could be expected on Mars because liquid water was certainly present on the surface of early Mars and carbon dioxide was abundant in its atmosphere. <span class="hlt">Calcite</span> is interesting because on Earth this mineral is produced by abiotic processes as well as by biological activity. One may suppose that crystalline defects and trace element in the <span class="hlt">crystal</span> lattice and the growth speed of biotic <span class="hlt">calcites</span> must indicate a difference between them and pure abiotic <span class="hlt">calcites</span>. We investigated twelve different terrestrial <span class="hlt">calcite</span> samples from various origins: biotic, diagenetic and abiotic. The minerals were studied by X-ray diffraction and electron scanning microscopy to determine their mineralogical and chemical composition, and differential thermal analysis coupled to thermogravimetric analysis (DTA-TG) to determine their thermal behavior. Our results show that the thermal degradation of abiotic <span class="hlt">calcite</span> starts at a temperature at least 40°C higher than the degradation temperature of any biotic <span class="hlt">calcite</span> investigated. Consequently, in the case of a Martian in-situ study or in a sample return mission, the analysis of Martian minerals by DTA-TG represents a promising approach to detect evidence of past biological activity on Mars.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005GeoRL..3223205S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005GeoRL..3223205S"><span>Search for past life on Mars: Physical and chemical characterization of minerals of biotic and abiotic origin: part 1 - <span class="hlt">Calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stalport, Fabien; Coll, Patrice; Cabane, Michel; Person, Alain; González, Rafael Navarro; Raulin, Francois; Vaulay, Marie Jo; Ausset, Patrick; McKay, Chris P.; Szopa, Cyril; Zarnecki, John</p> <p>2005-12-01</p> <p>Several lines of evidence suggest that early Mars once had liquid water on its surface, a denser atmosphere and a mild climate. Similar environmental conditions led to the origin of life on the Earth more than 3.5 billion years ago; consequently, life might also have originated on Mars. The Viking landers searched for evidence of organic molecules on the surface of Mars, and found that the Martian soil is depleted in organics at ppb levels at the landing sites. We contend that inorganic compounds could give us interesting clues as to the existence of possible biological activity in future astrobiological missions to Mars. Consequently, we have investigated the physical and chemical properties of <span class="hlt">calcite</span>, which could be expected on Mars because liquid water was certainly present on the surface of early Mars and carbon dioxide was abundant in its atmosphere. <span class="hlt">Calcite</span> is interesting because on Earth this mineral is produced by abiotic processes as well as by biological activity. One may suppose that crystalline defects and trace element in the <span class="hlt">crystal</span> lattice and the growth speed of biotic <span class="hlt">calcites</span> must indicate a difference between them and pure abiotic <span class="hlt">calcites</span>. We investigated twelve different terrestrial <span class="hlt">calcite</span> samples from various origins: biotic, diagenetic and abiotic. The minerals were studied by X-ray diffraction and electron scanning microscopy to determine their mineralogical and chemical composition, and differential thermal analysis coupled to thermogravimetric analysis (DTA-TG) to determine their thermal behavior. Our results show that the thermal degradation of abiotic <span class="hlt">calcite</span> starts at a temperature at least 40°C higher than the degradation temperature of any biotic <span class="hlt">calcite</span> investigated. Consequently, in the case of a Martian in-situ study or in a sample return mission, the analysis of Martian minerals by DTA-TG represents a promising approach to detect evidence of past biological activity on Mars.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/510301','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/510301"><span>Dissolution dynamics of the <span class="hlt">calcite</span>-water interface observed in situ by glancing-incidence X-ray scattering</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Sturchio, N.C.; Chiarello, R.P.</p> <p>1995-06-02</p> <p>Glancing-incidence X-ray scattering measurements made at the National Synchrotron Light Source were used to investigate dissolution dynamics in situ at the <span class="hlt">calcite</span>-water interface. The relation between <span class="hlt">calcite</span> saturation state and roughness of the <span class="hlt">calcite</span> (1014) cleavage surface as a function of time was examined during pH titrations of an initially <span class="hlt">calcite</span>-saturated solution. Systematic variations in roughness were observed as a function of saturation state as pH was titrated to values below that of <span class="hlt">calcite</span> saturation. Different steady-state values of roughness were evident at fixed values of {Delta}G{sub r}, and these were correlated with the extent of undersaturation. A significant increase in roughness begins to occur with increasing undersaturation at a {Delta}G{sub r} value of approximately {minus}2.0 kcal/mol. The dissolution rate corresponding to this increase is about 1.5 x 10{sup 7} mmol/cm {center_dot} sec. This increase in roughness is attributed to a transition in the principal rate-determining dissolution mechanism, and is consistent with both powder-reaction studies of dissolution kinetics and single-<span class="hlt">crystal</span> dissolution studies by atomic force microscopy. These data indicate some important potential applications of GIXS in the study of mineral-water interface geochemistry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18973965','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18973965"><span>Neptunium(V) adsorption to <span class="hlt">calcite</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Heberling, Frank; Brendebach, Boris; Bosbach, Dirk</p> <p>2008-12-12</p> <p>The migration behavior of the actinyl ions U(VI)O2(2+), Np(V)O2+ and Pu(V,VI)O2(+,2+) in the geosphere is to a large extend controlled by sorption reactions (inner- or outer-sphere adsorption, ion-exchange, coprecipitation/structural incorporation) with minerals. Here NpO2+ adsorption onto <span class="hlt">calcite</span> is studied in batch type experiments over a wide range of pH (6.0-9.4) and concentration (0.4 microM-40 microM) conditions. pH is adjusted by variation of CO2 partial pressure. Adsorption is found to be pH dependent with maximal adsorption at pH 8.3 decreasing with increasing and decreasing pH. pH dependence of adsorption decreases with increasing Np(V) concentration. EXAFS data of neptunyl adsorbed to <span class="hlt">calcite</span> and neptunyl in the supernatant shows differences in the Np(V)-O-yl distance, 1.85+/-0.01 angstroms for the adsorbed and 1.82+/-0.01 angstroms for the solution species. The equatorial environment of the neptunyl in solution shows about 5 oxygen neighbours at 2.45+/-0.02 angstroms. For adsorbed neptunyl there are also about 5 oxygen neighbours at 2.46+/-0.01 angstroms. An additional feature in the adsorbed species' R-space spectrum can be related to carbonate neighbours, 3 to 6 carbon backscatterers (C-eq) at 3.05+/-0.03 angstroms and 3 to 6 oxygen backscatterers (O-eq2) at 3.31+/-0.02 angstroms. The differences in the Np(V)-O-yl distance and the C-eq and O-eq2 backscatterers which are only present for the adsorbed species indicate inner-sphere bonding of the adsorbed neptunyl species to the <span class="hlt">calcite</span> surface. Experiments on adsorption kinetics indicate that after a fast surface adsorption process a continuous slow uptake occurs which may be explained by incorporation via surface dissolution and reprecipitation processes. This is also indicated by the part irreversibility of the adsorption as shown by increased KD values after desorption compared to adsorption.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MinPe.110..361C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MinPe.110..361C"><span><span class="hlt">Calcite</span> and dolomite in intrusive carbonatites. II. Trace-element variations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chakhmouradian, Anton R.; Reguir, Ekaterina P.; Couëslan, Christopher; Yang, Panseok</p> <p>2016-04-01</p> <p>The composition of <span class="hlt">calcite</span> and dolomite from several carbonatite complexes (including a large set of petrographically diverse samples from the Aley complex in Canada) was studied by electron-microprobe analysis and laser-ablation inductively-coupled-plasma mass-spectrometry to identify the extent of substitution of rare-earth and other trace elements in these minerals and the effects of different igneous and postmagmatic processes on their composition. Analysis of the newly acquired and published data shows that the contents of rare-earth elements (REE) and certain REE ratios in magmatic <span class="hlt">calcite</span> and dolomite are controlled by <span class="hlt">crystal</span> fractionation of fluorapatite, monazite and, possibly, other minerals. Enrichment in REE observed in some samples (up to ~2000 ppm in <span class="hlt">calcite</span>) cannot be accounted for by coupled substitutions involving Na, P or As. At Aley, the REE abundances and chondrite-normalized (La/Yb)cn ratios in carbonates decrease with progressive fractionation. Sequestration of heavy REE from carbonatitic magma by calcic garnet may be responsible for a steeply sloping "exponential" pattern and lowered Ce/Ce* ratios of <span class="hlt">calcite</span> from Magnet Cove (USA) and other localities. Alternatively, the low levels of Ce and Mn in these samples could result from preferential removal of these elements by Ce4+- and Mn3+-bearing minerals (such as cerianite and spinels) at increasing f(O2) in the magma. The distribution of large-ion lithophile elements (LILE = Sr, Ba and Pb) in rock-forming carbonates also shows trends indicative of <span class="hlt">crystal</span> fractionation effects (e.g., concomitant depletion in Ba + Pb at Aley, or Sr + Ba at Kerimasi), although the phases responsible for these variations cannot be identified unambiguously at present. Overall, element ratios sensitive to the redox state of the magma and its complexing characteristics (Eu/Eu*, Ce/Ce* and Y/Ho) are least variable and in both primary <span class="hlt">calcite</span> and dolomite, approach the average chondritic values. In consanguineous</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeCoA.200..310D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeCoA.200..310D"><span>Geochemistry of speleothems affected by aragonite to <span class="hlt">calcite</span> recrystallization - Potential inheritance from the precursor mineral</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Domínguez-Villar, David; Krklec, Kristina; Pelicon, Primož; Fairchild, Ian J.; Cheng, Hai; Edwards, Lawrence R.</p> <p>2017-03-01</p> <p>Formerly aragonite speleothems recrystallized to <span class="hlt">calcite</span> result from solutions subsaturated in aragonite and supersaturated in <span class="hlt">calcite</span> that infiltrate into the speleothem through the interconnected porosity. In most cases, the <span class="hlt">crystal</span> replacement takes place through a thin solution film. This diagenetic process can occur under open or semi-closed geochemical conditions. Thus, secondary <span class="hlt">calcite</span> <span class="hlt">crystals</span> record the composition of the fluid at the time of diagenesis affected by <span class="hlt">calcite</span> partition coefficients and fractionation factors (open system) or partly inherit the composition of the primary aragonite (semi-closed system). So, whether or not recrystallized aragonite speleothems can record reliable geochemical signals from the time of speleothem primary deposition still is an open debate. We studied a stalagmite from Eagle Cave (Spain) predominantly composed of secondary <span class="hlt">calcite</span> that replaced aragonite, although a core of primary aragonite extending 45 mm along the growth direction was preserved at the base of the sample. We obtained Mg and Sr compositional maps, paired U-Th dating and δ18O and δ13C profiles across the diagenetic front. Additionally, two parallel isotope records were obtained along the speleothem growth direction in the aragonite and <span class="hlt">calcite</span> sectors. Our results support that recrystallization of this speleothem took place in open system conditions for δ18O, δ13C, Mg and Sr, but in semi-closed system conditions for U and Th. The recrystallization of this sample took place during one or several events, likely after the Younger Dryas as a result of climate change influencing drip water composition. Based on compositional zoned patterns, we suggest that the advance of diagenetic fronts in this speleothem had an average rate of 50 ± 45 μm/yr. Such recrystallization rate can transform any aragonite speleothem into <span class="hlt">calcite</span> within a few centuries. We suggest that the volume of water interacting with the speleothem at the time of recrystallization is</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11738724','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11738724"><span>Urease activity in microbiologically-induced <span class="hlt">calcite</span> precipitation.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bachmeier, Keri L; Williams, Amy E; Warmington, John R; Bang, Sookie S</p> <p>2002-02-14</p> <p>The role of microbial urease in <span class="hlt">calcite</span> precipitation was studied utilizing a recombinant Escherichia coli HB101 containing a plasmid, pBU11, that encodes Bacillus pasteurii urease. The <span class="hlt">calcite</span> precipitation by E. coli HB101 (pBU11) was significant although its precipitation level was not as high as that by B. pasteurii. Addition of low concentrations (5-100 microM) of nickel, the cofactor of urease, to the medium further enhanced <span class="hlt">calcite</span> precipitation by E. coli (pBU11). <span class="hlt">Calcite</span> precipitation induced by both B. pasteurii and E. coli (pBU11) was inhibited in the presence of a urease inhibitor, acetohydroxamic acid (AHA). These observations on the recombinant urease have confirmed that urease activity is essential for microbiologically-induced <span class="hlt">calcite</span> precipitation. Partially purified B. pasteurii urease was immobilized in polyurethane (PU) foam to compare the efficacy of <span class="hlt">calcite</span> precipitation between the free and immobilized enzymes. The immobilized urease showed higher K(m) and lower V(max) values, which were reflected by a slower overall <span class="hlt">calcite</span> precipitation. However, scanning electron micrographs (SEM) identified that the <span class="hlt">calcite</span> precipitation occurred throughout the matrices of polyurethane. Furthermore, PU-immobilized urease retained higher enzymatic activities at high temperatures and in the presence of a high concentration of pronase, indicating that immobilization protects the enzyme activity from environmental changes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19720056937&hterms=calcite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dcalcite','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19720056937&hterms=calcite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dcalcite"><span>Emission polarization study on quartz and <span class="hlt">calcite</span>.</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Vincent, R. K.</p> <p>1972-01-01</p> <p>Calculation of the spectral emission polarization of quartz and <span class="hlt">calcite</span> polished plates for observation angles of 20 and 70 deg by the substitution of complex index of refraction values for each mineral into Fresnel's equations. The emission polarization is shown to be quite wavelength-dependent, demonstrating that selected narrow or medium-width spectral bands exhibit a significantly higher percentage of polarization than a broad spectral band for these two minerals. Field measurements with a broadband infrared radiometer yield polarizations on the order of 2% for a coarse-grained granite rock and beach sand (both quartz-rich). This implies that a more sensitive detector with a selected medium-width filter may be capable of measuring emission polarization accurately enough to make this parameter useful as a remote sensing tool for discrimination among rocks on the basis of texture.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_14 --> <div id="page_15" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="281"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999CoMP..134..217R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999CoMP..134..217R"><span>Comparison of garnet-biotite, <span class="hlt">calcite</span>-graphite, and <span class="hlt">calcite</span>-dolomite thermometry in the Grenville Orogen; Ontario, Canada</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rathmell, Mark A.; Streepey, Margaret M.; Essene, Eric J.; van der Pluijm, Ben A.</p> <p></p> <p>The Elzevir Terrane of the Grenville Orogen in southern Ontario contains metapelites and abundant graphitic marbles that were regionally metamorphosed from the upper greenschist to upper amphibolite facies. Comparative thermometry was undertaken with widely used calibrations for the systems garnet-biotite, <span class="hlt">calcite</span>-dolomite, and <span class="hlt">calcite</span>-graphite. Temperatures that are obtained from matrix biotites paired with prograde garnet near-rim analyses are usually consistent with those determined using <span class="hlt">calcite</span>-graphite thermometry. However, <span class="hlt">calcite</span>-graphite thermometry occasionally yields low temperatures due to lack of equilibration of anomalously light graphite. Application of <span class="hlt">calcite</span>-graphite and garnet-biotite systems may yield temperatures up to 70°C higher than <span class="hlt">calcite</span>-dolomite in amphibolite facies rocks. <span class="hlt">Calcite</span>-dolomite temperatures most closely approach those from <span class="hlt">calcite</span>-graphite and garnet-biotite when the samples contain a single generation of dolomite and <span class="hlt">calcite</span> grains contain no visible dolomite exsolution lamellae. However, some of these samples yield temperatures considerably lower than temperatures calculated from <span class="hlt">calcite</span>-graphite and garnet-biotite thermometry, indicating that the <span class="hlt">calcite</span>-dolomite thermometer may have been partially reset during retrogression. Estimated peak metamorphic temperatures of regional metamorphism between Madoc (upper greenschist facies) and Bancroft (upper amphibolite facies) range from 500 to 650°C. These results place the chlorite-staurolite isograd at 540°C, the kyanite-sillimanite isograd at 590°C, and the sillimanite-K-feldspar isograd at 650°C. Although each thermometer may have an absolute uncertainty of as much as +/-50°C, the 50 to 60°C temperature differences between the isograds are probably accurate to 10 to 20°C. An incomplete picture of the thermal gradients can result from the application of only one thermometer in a given area. Simultaneous application of several systems allows one to recognize and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1984JCrGr..66..639M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1984JCrGr..66..639M"><span>The influence of impurities on the growth rate of <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Meyer, H. J.</p> <p>1984-05-01</p> <p>The effects of 34 different additives on the growth rate of <span class="hlt">calcite</span> were investigated. An initial growth rate of about one <span class="hlt">crystal</span> monolayer (3 × 10 -8 cm) per minute was adjusted at a constant supersaturation which was maintained by a control circuit. Then the impurity was added step by step and the reduction of the growth rate was measured. The impurity concentration necessary to reduce the initial growth rate by a certain percentage increased in the order Fe 2+, ATP, P 3O 5-10, P 2O 4-7, (PO 3) 6-6, Zn 2+, ADP, Ce 3+, Pb 2+, carbamyl phosphate, Fe 3+, PO 3-4, Co 2+, Mn 2+, Be 2+, β-glycerophosphate, Ni 2+, Cd 2+, "Tris", phenylphosphate, chondroitine sulphate, Ba 2+, citrate, AMP, Sr 2+, tricarballylate, taurine, SO 2-4, Mg 2+ by 4 orders of magnitude. The most effective additives halved the initial growth rate in concentrations of 2 × 10 -8 mol/1. For Fe 2+ the halving concentration was nearly proportional to the initial rate. The mechanism of inhibition by adsorption of the impurities at growth sites (kinks) is discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22314443','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22314443"><span>Bent <span class="hlt">crystal</span> spectrometer for both frequency and wavenumber resolved x-ray scattering at a <span class="hlt">seeded</span> free-electron laser</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Zastrau, Ulf; Fletcher, Luke B.; Galtier, Eric Ch.; Gamboa, Eliseo; Glenzer, Siegfried H.; Heimann, Philipp; Nagler, Bob; Schropp, Andreas; Lee, Hae Ja; Förster, Eckhart; Marschner, Heike; Wehrhan, Ortrud</p> <p>2014-09-15</p> <p>We present a cylindrically curved GaAs x-ray spectrometer with energy resolution ΔE/E = 1.1 × 10{sup −4} and wave-number resolution of Δk/k = 3 × 10{sup −3}, allowing plasmon scattering at the resolution limits of the Linac Coherent Light Source (LCLS) x-ray free-electron laser. It spans scattering wavenumbers of 3.6 to 5.2/Å in 100 separate bins, with only 0.34% wavenumber blurring. The dispersion of 0.418 eV/13.5 μm agrees with predictions within 1.3%. The reflection homogeneity over the entire wavenumber range was measured and used to normalize the amplitude of scattering spectra. The proposed spectrometer is superior to a mosaic highly annealed pyrolytic graphite spectrometer when the energy resolution needs to be comparable to the LCLS <span class="hlt">seeded</span> bandwidth of 1 eV and a significant range of wavenumbers must be covered in one exposure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3331869','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3331869"><span>Evaluation of defects generation in crystalline silicon ingot grown by cast technique with <span class="hlt">seed</span> <span class="hlt">crystal</span> for solar cells</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Tachibana, Tomihisa; Sameshima, Takashi; Kojima, Takuto; Arafune, Koji; Kakimoto, Koichi; Miyamura, Yoshiji; Harada, Hirofumi; Sekiguchi, Takashi; Ohshita, Yoshio; Ogura, Atsushi</p> <p>2012-01-01</p> <p>Although crystalline silicon is widely used as substrate material for solar cell, many defects occur during <span class="hlt">crystal</span> growth. In this study, the generation of crystalline defects in silicon substrates was evaluated. The distributions of small-angle grain boundaries were observed in substrates sliced parallel to the growth direction. Many precipitates consisting of light elemental impurities and small-angle grain boundaries were confirmed to propagate. The precipitates mainly consisted of Si, C, and N atoms. The small-angle grain boundaries were distributed after the precipitation density increased. Then, precipitates appeared at the small-angle grain boundaries. We consider that the origin of the small-angle grain boundaries was lattice mismatch and/or strain caused by the high-density precipitation. PMID:22536006</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20863834','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20863834"><span><span class="hlt">Crystal</span> structure of an essential enzyme in <span class="hlt">seed</span> starch degradation: barley limit dextrinase in complex with cyclodextrins.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Vester-Christensen, Malene Bech; Abou Hachem, Maher; Svensson, Birte; Henriksen, Anette</p> <p>2010-11-12</p> <p>Barley limit dextrinase [Hordeum vulgare limit dextrinase (HvLD)] catalyzes the hydrolysis of α-1,6 glucosidic linkages in limit dextrins. This activity plays a role in starch degradation during germination and presumably in starch biosynthesis during grain filling. The <span class="hlt">crystal</span> structures of HvLD in complex with the competitive inhibitors α-cyclodextrin (CD) and β-CD are solved and refined to 2.5 Å and 2.1 Å, respectively, and are the first structures of a limit dextrinase. HvLD belongs to glycoside hydrolase 13 family and is composed of four domains: an immunoglobulin-like N-terminal eight-stranded β-sandwich domain, a six-stranded β-sandwich domain belonging to the carbohydrate binding module 48 family, a catalytic (β/α)(8)-like barrel domain that lacks α-helix 5, and a C-terminal eight-stranded β-sandwich domain of unknown function. The CDs are bound at the active site occupying carbohydrate binding subsites +1 and +2. A glycerol and three water molecules mimic a glucose residue at subsite -1, thereby identifying residues involved in catalysis. The bulky Met440, a unique residue at its position among α-1,6 acting enzymes, obstructs subsite -4. The steric hindrance observed is proposed to affect substrate specificity and to cause a low activity of HvLD towards amylopectin. An extended loop (Asp513-Asn520) between β5 and β6 of the catalytic domain also seems to influence substrate specificity and to give HvLD a higher affinity for α-CD than pullulanases. The <span class="hlt">crystal</span> structures additionally provide new insight into cation sites and the concerted action of the battery of hydrolytic enzymes in starch degradation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012GeCoA..91..202Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012GeCoA..91..202Y"><span>Differences in the immobilization of arsenite and arsenate by <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yokoyama, Yuka; Tanaka, Kazuya; Takahashi, Yoshio</p> <p>2012-08-01</p> <p>The sorption and coprecipitation experiments of arsenic (As) with <span class="hlt">calcite</span> coupled with determinations of the chemical state of As both in the reaction fluid and in <span class="hlt">calcite</span> were conducted to investigate the influence of the As oxidation state on its immobilization into <span class="hlt">calcite</span>. The oxidation states of As in <span class="hlt">calcite</span> and water were determined via As K-edge XANES and HPLC-ICP-MS analysis, respectively. The results of the sorption experiments at pH 8.2 show that only As(V) is distributed to <span class="hlt">calcite</span> regardless of the As oxidation state in the solution. In coprecipitation experiments, As(V) is preferentially incorporated into <span class="hlt">calcite</span> over a wide range of pH (7-12). On the other hand, the incorporation of As(III) into <span class="hlt">calcite</span> is not observed at circumneutral pH. This difference between As(III) and As(V) is attributed to the fact that their dissolved species are neutral vs. negatively charged, respectively, at circumneutral pH (arsenite as H3AsO3; arsenate as H2AsO4- or HAsO42-). As the pH increases (>9), up to 33% of As(III)/Astotal ratio is partitioned into <span class="hlt">calcite</span> or a precursor of <span class="hlt">calcite</span> (metastable vaterite formed during the early stage of precipitation). The higher interaction of As with <span class="hlt">calcite</span> at an alkaline pH compared with circumneutral pH is due to the negative charge of As(III) at alkaline pH. However, the As(III)/Astotal ratio decreases as time progresses and only As(V) can be found finally in <span class="hlt">calcite</span>. The ratio of distribution coefficients of As(III) and As(V) into <span class="hlt">calcite</span> (KAs(V)/KAs(III)) at pH ˜7 is larger than 2.1 × 103, suggesting that the oxidation state of As is a significant issue in considering the interaction between As and <span class="hlt">calcite</span> in groundwater. Moreover, low KAs(III) shows that the sequestration of As via coprecipitation with <span class="hlt">calcite</span> is not an important chemical process under reducing conditions, such as in the groundwaters in Bangladesh and other As-contaminated areas where As(III) is the dominant dissolved species of As. In the system spiked</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3273019','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3273019"><span><span class="hlt">Calcite</span> Biomineralization by Bacterial Isolates from the Recently Discovered Pristine Karstic Herrenberg Cave</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Rusznyák, Anna; Akob, Denise M.; Nietzsche, Sándor; Eusterhues, Karin; Totsche, Kai Uwe; Neu, Thomas R.; Frosch, Torsten; Popp, Jürgen; Keiner, Robert; Geletneky, Jörn; Katzschmann, Lutz; Schulze, Ernst-Detlef</p> <p>2012-01-01</p> <p>Karstic caves represent one of the most important subterranean carbon storages on Earth and provide windows into the subsurface. The recent discovery of the Herrenberg Cave, Germany, gave us the opportunity to investigate the diversity and potential role of bacteria in carbonate mineral formation. <span class="hlt">Calcite</span> was the only mineral observed by Raman spectroscopy to precipitate as stalactites from seepage water. Bacterial cells were found on the surface and interior of stalactites by confocal laser scanning microscopy. Proteobacteria dominated the microbial communities inhabiting stalactites, representing more than 70% of total 16S rRNA gene clones. Proteobacteria formed 22 to 34% of the detected communities in fluvial sediments, and a large fraction of these bacteria were also metabolically active. A total of 9 isolates, belonging to the genera Arthrobacter, Flavobacterium, Pseudomonas, Rhodococcus, Serratia, and Stenotrophomonas, grew on alkaline carbonate-precipitating medium. Two cultures with the most intense precipitate formation, Arthrobacter sulfonivorans and Rhodococcus globerulus, grew as aggregates, produced extracellular polymeric substances (EPS), and formed mixtures of <span class="hlt">calcite</span>, vaterite, and monohydrocalcite. R. globerulus formed idiomorphous <span class="hlt">crystals</span> with rhombohedral morphology, whereas A. sulfonivorans formed xenomorphous globular <span class="hlt">crystals</span>, evidence for taxon-specific <span class="hlt">crystal</span> morphologies. The results of this study highlighted the importance of combining various techniques in order to understand the geomicrobiology of karstic caves, but further studies are needed to determine whether the mineralogical biosignatures found in nutrient-rich media can also be found in oligotrophic caves. PMID:22179248</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22179248','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22179248"><span><span class="hlt">Calcite</span> biomineralization by bacterial isolates from the recently discovered pristine karstic herrenberg cave.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rusznyák, Anna; Akob, Denise M; Nietzsche, Sándor; Eusterhues, Karin; Totsche, Kai Uwe; Neu, Thomas R; Frosch, Torsten; Popp, Jürgen; Keiner, Robert; Geletneky, Jörn; Katzschmann, Lutz; Schulze, Ernst-Detlef; Küsel, Kirsten</p> <p>2012-02-01</p> <p>Karstic caves represent one of the most important subterranean carbon storages on Earth and provide windows into the subsurface. The recent discovery of the Herrenberg Cave, Germany, gave us the opportunity to investigate the diversity and potential role of bacteria in carbonate mineral formation. <span class="hlt">Calcite</span> was the only mineral observed by Raman spectroscopy to precipitate as stalactites from seepage water. Bacterial cells were found on the surface and interior of stalactites by confocal laser scanning microscopy. Proteobacteria dominated the microbial communities inhabiting stalactites, representing more than 70% of total 16S rRNA gene clones. Proteobacteria formed 22 to 34% of the detected communities in fluvial sediments, and a large fraction of these bacteria were also metabolically active. A total of 9 isolates, belonging to the genera Arthrobacter, Flavobacterium, Pseudomonas, Rhodococcus, Serratia, and Stenotrophomonas, grew on alkaline carbonate-precipitating medium. Two cultures with the most intense precipitate formation, Arthrobacter sulfonivorans and Rhodococcus globerulus, grew as aggregates, produced extracellular polymeric substances (EPS), and formed mixtures of <span class="hlt">calcite</span>, vaterite, and monohydrocalcite. R. globerulus formed idiomorphous <span class="hlt">crystals</span> with rhombohedral morphology, whereas A. sulfonivorans formed xenomorphous globular <span class="hlt">crystals</span>, evidence for taxon-specific <span class="hlt">crystal</span> morphologies. The results of this study highlighted the importance of combining various techniques in order to understand the geomicrobiology of karstic caves, but further studies are needed to determine whether the mineralogical biosignatures found in nutrient-rich media can also be found in oligotrophic caves.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.B43G..06W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.B43G..06W"><span>Investigating the Physical Basis of Amorphous Precursor Transformation to <span class="hlt">Calcite</span> Using Patterned Alkanethiol Surfaces</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, D.; Wallace, A.; Han, T. Y.; Lee, J. R.; Hailey, P. D.; de Yoreo, J. J.; Dove, P. M.</p> <p>2007-12-01</p> <p>Increasing evidence from X-ray Absorption Spectroscopy and Environmental Scanning Electron Microscopy (ESEM) studies of biominerals extracted from calcifying organisms show that amorphous calcium carbonate (ACC) plays a key role in the initial formation of carbonate minerals and in shaping them into complex morphologies. Echinoderms and possibly a wide variety of other organisms, use ACC as a precursor phase. The ACC is first formed within spatial and temporally controlled environments such as vesicles, followed by a subsequent onset of mineralization that transforms the precursor into a fully crystalline material. Recent studies on sea urchin embryos have shown that during this transformation, ACC develops short-range order that resembles <span class="hlt">calcite</span> before fully <span class="hlt">crystallizing</span>. While this "non-traditional" process is recognized, the mechanisms and factors that govern this transformation remain poorly understood. Of particular interest are the roles of water, and the functional group chemistry of surfaces and macromolecules within mineralization environments. To investigate these questions, we have developed an experimental approach using ESEM that allows us to control impurity concentration, surface functionality and water content through the degree of water condensation. Patterned self-assembled monolayers (SAM) of hydrophilic moieties with domains of approximately 25 microns in diameter are used to form an array of micro-reactors. ACC particles with known composition are then deposited on the patterns. Condensing water in the ESEM initializes the transformation of ACC to <span class="hlt">calcite</span>. Our results show that in saturated water vapor, ACC swells, but no obvious faceting of the material occurs. It is only in bulk water, via dissolution/<span class="hlt">crystallization</span>, where the <span class="hlt">calcite</span> grown on carboxyl-terminated surfaces is found with the often-observed \\{013\\} nucleation face. We use this insight to understand the role of the different chemical moieties on ACC to <span class="hlt">calcite</span> transformation</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/7079128','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/7079128"><span><span class="hlt">Calcitization</span> and silicification of evaporites in Guadalupian back-reef carbonates of the Delaware basin, west Texas and New Mexico</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ulmer, D.S.; Scholle, P.A. )</p> <p>1991-03-01</p> <p>Outcrop of the Seven Rivers, Yates, and Tansill formations contain numerous examples of evaporites that have been replaced by both quartz and <span class="hlt">calcite</span>. The original evaporites consisted of discrete horizons, scattered nodules, enterolithic layers, and individual <span class="hlt">crystal</span> laths of gypsum and/or anhydrite within a predominantly dolomitic matrix. Based on field and petrographic observations, evaporite replacement proceeded from the exterior to the interior of the nodules. The earliest replacement was by euhedral, black megaquartz containing abundant hydrocarbon inclusions. <span class="hlt">Calcite</span> replacement followed silicification and consists of coarse, equant, blocky spar. Isotopic analyses of these <span class="hlt">calcites</span> form two distinct groups: the first group ranges from -10.9 to -20.1{per thousand} (average -16.4{per thousand}) {delta}{sup 13}C and -6.4 to -13.8{per thousand} (average -10.9{per thousand}) {delta}{sup 18}O; the second group ranges from +1.4 to 5.8{per thousand} (average -2.4{per thousand}) {delta}{sup 13}C and -6.2 to 14.1{per thousand} (average -9.2{per thousand}) {delta}{sup 18}O. Evaporite silicification was coeval with hydrocarbon migration as indicated by the inclusion data. <span class="hlt">Calcitization</span>, however, was associated with mid-Tertiary block faulting that uplifted the area causing deep groundwater circulation. The isotopically very light <span class="hlt">calcites</span> resulted from the mixing of meteoric fluids and hydrocarbon-rich pore fluids, probably during early uplift while these strata were still at significant depth. The <span class="hlt">calcites</span> with heavier isotopic values were produced somewhat later by meteoric fluids that had little or no contact with hydrocarbons. Evaporite diagenesis in the Delaware basin is an ongoing process that started during hydrocarbon migration, continued over millions of years, and has the potential to significantly change the porosity of these units.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AnRMS..41...21W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AnRMS..41...21W"><span><span class="hlt">Crystallization</span> Pathways in Biomineralization</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Weiner, Steve; Addadi, Lia</p> <p>2011-08-01</p> <p>A <span class="hlt">crystallization</span> pathway describes the movement of ions from their source to the final product. Cells are intimately involved in biological <span class="hlt">crystallization</span> pathways. In many pathways the cells utilize a unique strategy: They temporarily concentrate ions in intracellular membrane-bound vesicles in the form of a highly disordered solid phase. This phase is then transported to the final mineralization site, where it is destabilized and <span class="hlt">crystallizes</span>. We present four case studies, each of which demonstrates specific aspects of biological <span class="hlt">crystallization</span> pathways: seawater uptake by foraminifera, <span class="hlt">calcite</span> spicule formation by sea urchin larvae, goethite formation in the teeth of limpets, and guanine <span class="hlt">crystal</span> formation in fish skin and spider cuticles. Three representative <span class="hlt">crystallization</span> pathways are described, and aspects of the different stages of <span class="hlt">crystallization</span> are discussed. An in-depth understanding of these complex processes can lead to new ideas for synthetic <span class="hlt">crystallization</span> processes of interest to materials science.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/912209','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/912209"><span>Strontium Incorporation into <span class="hlt">Calcite</span> Generated by Bacterial Ureolysis</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Yoshiko Fujita; George D. Redden; Jani C. Ingram; Marnie M. Cortez; Robert W. Smith</p> <p>2004-08-01</p> <p>Strontium incorporation into <span class="hlt">calcite</span> generated by bacterial ureolysis was investigated as part of an assessment of a proposed remediation approach for 90Sr contamination in groundwater. Urea hydrolysis produces ammonium and carbonate and elevates pH, resulting in the promotion of calcium carbonate precipitation. Urea hydrolysis by the bacterium Bacillus pasteurii in a medium designed to mimic the chemistry of the Snake River Plain Aquifer in Idaho resulted in a pH rise from 7.5 to 9.1. Measured average distribution coefficients (DEX) for Sr in the <span class="hlt">calcite</span> produced by ureolysis (0.5) were up to an order of magnitude higher than values reported in the literature for natural and synthetic <span class="hlt">calcites</span> (0.02–0.4). They were also higher than values for <span class="hlt">calcite</span> produced abiotically by ammonium carbonate addition (0.3). The precipitation of <span class="hlt">calcite</span> in these experiments was verified by X-ray diffraction. Time-of-flight secondary ion mass spectrometry (ToF SIMS) depth profiling (up to 350 nm) suggested that the Sr was not merely sorbed on the surface, but was present at depth within the particles. X-ray absorption near edge spectra showed that Sr was present in the <span class="hlt">calcite</span> samples as a solid solution. The extent of Sr incorporation appeared to be driven primarily by the overall rate of <span class="hlt">calcite</span> precipitation, where faster precipitation was associated with greater Sr uptake into the solid. The presence of bacterial surfaces as potential nucleation sites in the ammonium carbonate precipitation treatment did not enhance overall precipitation or the Sr distribution coefficient. Because bacterial ureolysis can generate high rates of <span class="hlt">calcite</span> precipitation, the application of this approach is promising for remediation of 90Sr contamination in environments where <span class="hlt">calcite</span> is stable over the long term.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/878670','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/878670"><span>Magnesium inhibition of <span class="hlt">calcite</span> dissolution kinetics</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Arvidson, Rolf S.; Collier, Martin; Davis, Kevin J.; Vinson, Michael D.; Amonette, James E.; Luttge, Andreas</p> <p>2006-02-01</p> <p>We present evidence of inhibition of <span class="hlt">calcite</span> dissolution by dissolved magnesium through direct observations of the (104) surface using atomic force microscopy (AFM) and vertical scanning interferometry (VSI). Far from equilibrium, the pattern of magnesium inhibition is dependent on solution composition and specific to surface step geometry. In CO2-free solutions (pH 8.8), dissolved magnesium brings about little inhibition even at concentrations of 0.8 x 10-3 molal. At the same pH, magnesium concentrations of less than 0.05 x 10-3 molal in carbonate-buffered solutions generate significant inhibition, although no changes in surface and etch pit morphology are observed. As concentrations exceed magnesite saturation, the dissolution rate shows little additional decrease; however, selective pinning of step edges results in unique etch-pit profiles, seen in both AFM and VSI datasets. Despite the decreases in step velocity, magnesium addition in carbonated solutions also appears to activate the surface by increasing the nucleation rate of new defects. These relationships suggest that the modest depression of the bulk rate measured by VSI reflects a balance between competing reaction mechanisms that simultaneously depress the rate through selective inhibition of step movement, but also enhance reactivity on terraces by lowering the energy barrier to new etch-pit formation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70017468','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70017468"><span>High-pressure deformation of <span class="hlt">calcite</span> marble and its transformation to aragonite under non-hydrostatic conditions</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hacker, B.R.; Kirby, S.H.</p> <p>1993-01-01</p> <p>We conducted deformation experiments on Carrara marble in the aragonite and <span class="hlt">calcite</span> stability fields to observe the synkinematic transformation of <span class="hlt">calcite</span> to aragonite, and to identify any relationships between transformation and deformation or sample strength. Deformation-induced microstructures in <span class="hlt">calcite</span> <span class="hlt">crystals</span> varied most significantly with temperature, ranging from limited slip and twinning at 400??C, limited recrystallization at 500??C, widespread recrystallization at 600 and 700??C, to grain growth at 800-900??C. Variations in confining pressure from 0.3 to 2.0 GPa have no apparent effect on <span class="hlt">calcite</span> deformation microstructures. Aragonite grew in 10-6-10-7 s-1strain rate tests conducted for 18-524 h at confining pressures of 1.7-2.0 GPa and temperatures of 500-600??C. As in our previously reported hydrostatic experiments on this same transformation, the aragonite nucleated on <span class="hlt">calcite</span> grain boundaries. The extent of transformation varied from a few percent conversion near pistons at 400??C, 2.0 GPa and 10-4 s-1 strain rate in a 0.8 h long experiment, to 98% transformation in a 21-day test at a strain rate of 10-7 s-7, a temperature of 600??C and a pressure of 2.0 GPa. At 500??C, porphyroblastic 100-200 ??m aragonite <span class="hlt">crystals</span> grew at a rate faster than 8 ?? 10-1m s-1. At 600??C, the growth of aragonite neoblasts was slower, ???6 ?? 10-1 m s -1, and formed 'glove-and-finger' cellularprecipitation-like textures identical to those observed in hydrostatic experiments. The transformation to aragonite is not accompanied by a shear instability or anisotropic aragonite growth, consistent with its relatively small volume change and latent heat in comparison with compounds that do display those features. ?? 1993.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/7159007','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/7159007"><span>Subaerial meteoric <span class="hlt">calcitization</span> and lithification of high-magnesian <span class="hlt">calcite</span> muds, Belize</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mazzullo, S.J.; Bischoff, W.D. )</p> <p>1991-03-01</p> <p>Holocene ({lt}1000-1500 yrs old) high-magnesian <span class="hlt">calcite</span>-dominated muddy sediments (1 m thick) on subaerially exposed cays in northern Belize are in the process of being converted to low-magnesian <span class="hlt">calcite</span> micrite. Mineralogic stabilization and attendant lithification result from interaction of the sediments with meteoric fluids believed to be derived from seasonal upward discharge through subjacent Pleistocene limestones. The initial marine-derived sediments, composed of {gt}85% HMC (and minor skeletal aragonite), consist of mud and associated soritid and miliolid foraminifera both with MgCO{sub 3} content of 11-15 mol%, and isotopic compositions of -1.0 to -2.5{per thousand} PDB (O), 0 to +1.5{per thousand} PDB (C). With depth, lithified LMC crusts appear in the section, and the Mg concentration of the sediments and associated crusts decreases rapidly to 3 mol% or less, with a corresponding isotopic depletion to values approaching -7.0{per thousand} (O) and -5.8{per thousand} (C). Concomitantly there is progressive dissolution of skeletal aragonite in the sediments, reduction of porosity due to cementation by LMC, and in the muds, a decrease in Sr and increase in Mn contents. The resultant petrofabric of these lithified LMC deposits, derived from the alteration of HMC-dominated muds, is characterized by micrite with patches of pore-filling micritic and microsparitic LMC cements. Such a fabric is similar to and can be confused easily with <span class="hlt">calcitized</span> aragonite-dominated precursor muds, except for the relative rarity in the samples examined of aragonite relicts in component microspar and/or pseudospar.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012GeCoA..92...23W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012GeCoA..92...23W"><span>Climate and cave control on Pleistocene/Holocene <span class="hlt">calcite</span>-to-aragonite transitions in speleothems from Morocco: Elemental and isotopic evidence</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wassenburg, Jasper A.; Immenhauser, Adrian; Richter, Detlev K.; Jochum, Klaus Peter; Fietzke, Jan; Deininger, Michael; Goos, Manuela; Scholz, Denis; Sabaoui, Abdellah</p> <p>2012-09-01</p> <p>The occurrence of aragonite in speleothems has commonly been related to high dripwater Mg/Ca ratios, because Mg is known to be a growth inhibitor for <span class="hlt">calcite</span>. Laboratory aragonite precipitation experiments, however, suggested a more complex array of controlling factors. Here, we present data from Pleistocene to Holocene speleothems collected from both a dolostone and a limestone cave in northern Morocco. These stalagmites exhibit both lateral and stratigraphic <span class="hlt">calcite</span>-to-aragonite transitions. Aragonite fabrics are well-preserved and represent primary features. In order to shed light on the factors that control alternating <span class="hlt">calcite</span> and aragonite precipitation, elemental (Mg, Sr, Ba, U, P, Y, Pb, Al, Ti and Th) abundances were measured using LA-ICP-MS, and analysed with Principal Component Analysis. Samples were analyzed at 100-200 μm resolution across stratigraphic and lateral transitions. Carbon and oxygen isotope ratios were analysed at 100 μm resolution covering stratigraphic <span class="hlt">calcite</span>-to-aragonite transitions. Results show that the precipitation of aragonite was driven by a decrease in effective rainfall, which enhanced prior <span class="hlt">calcite</span> precipitation. Different geochemical patterns are observed between <span class="hlt">calcite</span> and aragonite when comparing data from the Grotte de Piste and Grotte Prison de Chien. This may be explained by the increased dripwater Mg/Ca ratio and enhanced prior aragonite precipitation in the dolostone cave versus lower dripwater Mg/Ca ratio and prior <span class="hlt">calcite</span> precipitation in the limestone cave. A full understanding for the presence of lateral <span class="hlt">calcite</span>-to-aragonite transitions is not reached. Trace elemental analysis, however, does suggest that different crystallographic parameters (ionic radius, amount of <span class="hlt">crystal</span> defect sites, adsorption potential) may have a direct effect on the incorporation of Sr, Mg, Ba, Al, Ti, Th and possibly Y and P.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012GeCoA..84..217D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012GeCoA..84..217D"><span>Trace metal distribution and isotope variations in low-temperature <span class="hlt">calcite</span> and groundwater in granitoid fractures down to 1 km depth</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Drake, Henrik; Tullborg, Eva-Lena; Hogmalm, K. Johan; Åström, Mats E.</p> <p>2012-05-01</p> <p> methods used depended on the <span class="hlt">crystal</span> homogeneity (one or several <span class="hlt">calcite</span> generations), discerned by detailed SEM-investigations (back-scatter and cathodo-luminescence). 87Sr/86Sr ratios as well as δ18O signatures in <span class="hlt">calcite</span> are in the range expected for the precipitates from present-day groundwater, or older groundwater with similar composition (except in sections with a considerable portion of glacial water, where <span class="hlt">calcite</span> definitely is older than the latest glaciation). Stable carbon isotopes in <span class="hlt">calcite</span> generally show values typically associated with HCO3- originating from soil organic matter but at intermediate depth frequently with HCO3- originating from in situ microbial anaerobic oxidation of methane (highly depleted δ13C). For one of the studied metals - manganese - there was a strong correlation between the sampled <span class="hlt">calcite</span> coatings and hypothetical <span class="hlt">calcite</span> predicted by applying laboratory-based partition coefficients (literature data) on groundwater chemistry for sections corresponding to those where the <span class="hlt">calcites</span> were sampled. This points to temporal and spatial stability in groundwater Mn/Ca ratios over millions of years, or even more, and show that it is possible to assess, based on laboratory-derived data on Mn partitioning, past groundwater Mn-composition from fracture <span class="hlt">calcites</span>. For other metals - Fe, Sr, and Mg - which are expected to interact with co-precipitating minerals to a higher degree than Mn, the correlations between measured and predicted <span class="hlt">calcite</span> were weaker for various reasons.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/60996','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/60996"><span>Paleoclimatic and paleohydrologic records from secondary <span class="hlt">calcite</span>: Yucca Mountain, Nevada</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Whelan, J.F.; Stuckless, J.S.; Moscati, R.J.; Vaniman, D.T.</p> <p>1994-12-31</p> <p>Stable isotope analyses of <span class="hlt">calcite</span> and opal, fluid inclusion formation conditions and gas compositions, Sr isotope ratios, and REE compositions all support formation of secondary <span class="hlt">calcite</span> in the unsaturated zone of Yucca Mountain from infiltration of surface-derived (and soil zone buffered) waters of meteoric origin. Detailed sampling of growth-banding preserved by the secondary <span class="hlt">calcite</span> should provide a record of past variations in the stable isotope chemistry of these infiltrating waters, and, hence, of precipitation at Yucca Mountain, i.e., a proxy of past climate at Yucca Mountain. The precision of this record depends on how well it can be dated. The distribution and texture of secondary <span class="hlt">calcite</span> occurrences, if mapped in careful detail from existing bore hole samples and underground workings (as exposures become accessible), could provide a time/space map of fracture and fault unsaturated-zone ground water flow-paths during past wetter climates which might prevail in the future with change in climate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20090012293','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20090012293"><span>Relative Shock Effects in Mixed Powders of <span class="hlt">Calcite</span>, Gypsum, and Quartz: A Calibration Scheme from Shock Experiments</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bell, Mary S.</p> <p>2009-01-01</p> <p>The shock behavior of <span class="hlt">calcite</span> and gypsum is important in understanding the Cretaceous/Tertiary event and other terrestrial impacts that contain evaporite sediments in their targets. Most interest focuses on issues of devolatilization to quantify the production of CO2 or SO2 to better understand their role in generating a temporary atmosphere and its effects on climate and biota [e.g., papers in 1,2,3,4]. Devolatilization of carbonate is also important because the dispersion and fragmentation of ejecta is strongly controlled by the expansion of large volumes of gas during the impact process as well [5,6]. Shock recovery experiments for <span class="hlt">calcite</span> yield seemingly conflicting results: early experimental devolatilization studies [7,8,9] suggested that <span class="hlt">calcite</span> was substantially outgassed at 30 GPa (> 50%). However, the recent petrographic work of [10,11,12] presented evidence that essentially intact <span class="hlt">calcite</span> is recovered from 60 GPa experiments. [13] reported results of shock experiments on anhydrite, gypsum, and mixtures of those phases with silica. Their observations indicate little or no devolatilization of anhydrite shocked to 42 GPa and that the fraction of sulfur, by mass, that degassed is approx.10(exp -2) of theoretical prediction. In another (preliminary) report of shock experiments on <span class="hlt">calcite</span>, anhydrite, and gypsum, [14] observe <span class="hlt">calcite</span> recrystallization when shock loaded at 61 GPa, only intensive plastic deformation in anhydrite shock loaded at 63 GPa, and gypsum converted to anhydrite when shock loaded at 56 GPa. [15] shock loaded anhydrite and quartz to a peak pressure of 60 GPa. All of the quartz grains were trans-formed to glass and the platy anhydrite grains were completely pseudomorphed by small <span class="hlt">crystallized</span> anhydrite grains. However, no evidence of interaction between the two phases could be observed and they suggest that recrystallization of anhydrite grains is the result of a solid state transformation. [16] reanalyzed the <span class="hlt">calcite</span> and anhydrite shock</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EGUGA..1112962R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..1112962R"><span>An AFM study of <span class="hlt">calcite</span> dissolution in concentrated electrolyte solutions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ruiz Agudo, E.; Putnis, C. V.; Putnis, A.; Rodriguez-Navarro, C.</p> <p>2009-04-01</p> <p><span class="hlt">Calcite</span>-solution interactions are of a paramount importance in a range of processes such as the removal of heavy metals, carbon dioxide sequestration, landscape modeling, weathering of building stone and biomineralization. Water in contact with minerals often carries significant amounts of solutes; additionally, their concentration may vary due to evaporation and condensation. It is well known that <span class="hlt">calcite</span> dissolution is affected dramatically by the presence of such solutes. Here we present investigations on the dissolution of <span class="hlt">calcite</span> in the presence of different electrolytes. Both bulk (batch reactors) experiments and nanoscale (in situ AFM) techniques are used to study the dissolution of <span class="hlt">calcite</span> in a range of solutions containing alkaly cations balanced by halide anions. Previous works have indicated that the ionic strength has little influence in <span class="hlt">calcite</span> dissolution rates measured from bulk experiments (Pokrovsky et al. 2005; Glendhill and Morse, 2004). Contrary to these results, our quantitative analyses of AFM observations show an enhancement of the <span class="hlt">calcite</span> dissolution rate with increasing electrolyte concentration. Such an effect is concentration-dependent and it is most evident in concentrated solutions. AFM experiments have been carried out in a fluid cell using <span class="hlt">calcite</span> cleavage surfaces in contact with solutions of simple salts of the alkaly metals and halides at different undersaturations with respect to <span class="hlt">calcite</span> to try to specify the effect of the ionic strength on etch pit spreading rate and <span class="hlt">calcite</span> dissolution rate. These results show that the presence of soluble salts may critically affect the weathering of carbonate rocks in nature as well as the decay of carbonate stone in built cultural heritage. References: Pokrosky, O.S.; Golubev, S.V.; Schott, J. Dissolution kinetics of <span class="hlt">calcite</span>, dolomite and magnesite at 25°C and 0 to 50 atm pCO2. Chemical Geology, 2005, 217 (3-4) 239-255. Glendhill, D.K.; Morse, J.W. Dissolution kinetics of <span class="hlt">calcite</span> in Na</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/992616','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/992616"><span>Kinetics and Mechanisms of <span class="hlt">Calcite</span> Reactions with Saline Waters</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Chapman, Piers; *Morse, John W.</p> <p>2010-11-15</p> <p>1. Objective The general objective of this research was to determine the kinetics and mechanisms of <span class="hlt">calcite</span> reactions with saline waters over a wide range of saline water composition, carbon dioxide partial pressure (pCO2), and modest ranges of T and P. This would be done by studying both reaction rates and solubility from changes in solution chemistry. Also, nanoscale observations of <span class="hlt">calcite</span> surface morphology and composition would be made to provide an understanding of rate controlling mechanisms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMMR33B2657M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMMR33B2657M"><span>Microstructure and frictional properties of sheared <span class="hlt">calcite</span> speleothems: natural vs. experimental investigation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mitrovic, I.; Tesei, T.; Grasemann, B.; Collettini, C.; Plan, L.; Baron, I.</p> <p>2015-12-01</p> <p>Several alpine caves in Austria preserve evidences related to active faulting, such as broken and scratched speleothems. Here, in order to better understand fault slip behavior and related potential earthquake hazards, microstructures of experimentally deformed speleothems are presented and compared with naturally deformed ones. Speleothems are monomineralitic rocks precipitated in caves, composed of columnar centimeter-scale <span class="hlt">calcite</span> <span class="hlt">crystals</span> with strong growth orientation. In order to better study the origin and evolution of deformation in faulted speleothems we performed sliding experiments using a rock deformation biaxial apparatus. In order to recreate the faulting conditions observed in Austrian caves, speleothems were cut into rectangular blocks and sheared against each other, with long growth axes of <span class="hlt">calcite</span> perpendicular to the shearing direction. The experiments were performed under room conditions, sliding velocity in the range of 0.001-0.01 mm/s, and constant effective normal stress of 3 MPa. The mechanical data show fairly high friction coefficient (0.7-0.95) accompanied by the production of <span class="hlt">calcite</span>-rich fault gouge which displays Riedel shears within a foliated cataclasite and drastic grain size reduction (nano-scale). The transition from the fault gouge towards the undeformed <span class="hlt">crystals</span> is characterized first by a series of in situ jigsaw puzzle fracturing, then dense mechanical twin network, which is decreasing in its intensity away from the gouge (i.e. principal slip surface). The similarity between laboratory induced and naturally formed microstructures reinforce the tectonic interpretation of the damaged speleothems. Detailed microstructure investigations, including electron backscattered diffraction technique combined with electron microprobe and cathodoluminescence, are on the way to help distinguishing between seismic slip and/or aseismic creep.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016E%26PSL.442...13P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016E%26PSL.442...13P"><span>Palaeotemperature reconstruction during the Last Glacial from δ18O of earthworm <span class="hlt">calcite</span> granules from Nussloch loess sequence, Germany</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Prud'homme, Charlotte; Lécuyer, Christophe; Antoine, Pierre; Moine, Olivier; Hatté, Christine; Fourel, François; Martineau, François; Rousseau, Denis-Didier</p> <p>2016-05-01</p> <p>The Nussloch loess-palaeosol sequence (Rhine Valley, Germany) is considered to be one of the most complete records of the last glacial period in Western Europe due to its very high sedimentation rate and its good chronological control. This sequence is therefore a good framework in which to develop new proxies for palaeoenvironmental reconstructions. In this study, we explore, for the first time, the potential of earthworm <span class="hlt">calcite</span> granules as a new bio-indicator and climatic proxy of absolute air and soil temperature in the context of Last Glacial loess. These granules are composed of rhomboedric <span class="hlt">calcite</span> <span class="hlt">crystals</span>, organized in a radial crystalline structure. As these granules are individually generated by earthworms at a relative fast rate, they are expected to record intra-annual variations in the available sources of oxygen: percolating waters of meteoric origin. We extracted thirty earthworm <span class="hlt">calcite</span> granules from 11 of 5 cm layers thick from tundra gley and brown soil horizons previously, dated at 45 to 23 ka. Oxygen isotope ratios were measured on each individual granule. The δ18O of <span class="hlt">calcite</span> granules and interlinked transfer functions between water cycle, air and soil temperatures allowed us to estimate air temperatures ranging from 10 to 12 ± 4°C, which most likely reflect the warm periods of the year when earthworms were the most active.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1028603','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1028603"><span>The differnces between bond lengths in biogenic and geologocal <span class="hlt">calcite</span>.</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Zlotoyabko, E.; Caspi, E. N.; Fieramosca, J. S.; Von Dreele, R. B.; Marin, F.; Mor, G.; Politi, Y.; Addadi, L.; Weiner, S.</p> <p>2010-01-01</p> <p>We used high-resolution neutron powder diffraction to accurately measure the atomic positions and bond lengths in biogenic and geological <span class="hlt">calcite</span>. A special procedure for data analysis was developed in order to take into account the considerable amounts of magnesium present in all the investigated samples. As a result, in biogenic <span class="hlt">calcite</span> we found some atomic bonds to have significantly different lengths as compared to those in geological <span class="hlt">calcite</span>, after the contribution of magnesium is accounted for. The maximum effect (elongation up to 0.7%) was found for the C-O bonds. We also analyzed changes in frequencies and spectral widths of normal vibrations of carbonate groups in biogenic <span class="hlt">calcite</span> (as compared to geological <span class="hlt">calcite</span>) measured by Raman and Fourier transform IR techniques. Surprisingly, the frequency shifts after subtracting the magnesium contribution are close to zero. At the same time, substantial spectral broadening (up to 1.2%) in biogenic <span class="hlt">calcite</span> as compared to geological samples was detected. Possible explanations for the experimental findings are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeCoA.170...51S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeCoA.170...51S"><span>A novel determination of <span class="hlt">calcite</span> dissolution kinetics in seawater</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Subhas, Adam V.; Rollins, Nick E.; Berelson, William M.; Dong, Sijia; Erez, Jonathan; Adkins, Jess F.</p> <p>2015-12-01</p> <p>We present a novel determination of the dissolution kinetics of inorganic <span class="hlt">calcite</span> in seawater. We dissolved 13 C -labeled <span class="hlt">calcite</span> in unlabeled seawater, and traced the evolving δ13 C composition of the fluid over time to establish dissolution rates. This method provides sensitive determinations of dissolution rate, which we couple with tight constraints on both seawater saturation state and surface area of the dissolving minerals. We have determined dissolution rates for two different abiotic <span class="hlt">calcite</span> materials and three different grain sizes. Near-equilibrium dissolution rates are highly nonlinear, and are well normalized by geometric surface area, giving an empirical dissolution rate dependence on saturation state (Ω) of: This result substantiates the non-linear response of <span class="hlt">calcite</span> dissolution to undersaturation. The bulk dissolution rate constant calculated here is in excellent agreement with those determined in far from equilibrium and dilute solution experiments. Plots of dissolution versus undersaturation indicates the presence of at least two dissolution mechanisms, implying a criticality in the <span class="hlt">calcite</span>-seawater system. Finally, our new rate determination has implications for modeling of pelagic and seafloor dissolution. Nonlinear dissolution kinetics in a simple 1-D lysocline model indicate a possible transition from kinetic to diffusive control with increasing water depth, and also confirm the importance of respiration-driven dissolution in setting the shape of the <span class="hlt">calcite</span> lysocline.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1817458S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1817458S"><span><span class="hlt">Calcite</span> precipitation on glass substrates and active stalagmites in Katerloch Cave (Austria): Constraints from environmental monitoring</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sakoparnig, Marlene; Boch, Ronny; Wang, Xianfeng; Lin, Ke; Spötl, Christoph; Leis, Albrecht; Gollowitsch, Anna; Dietzel, Martin</p> <p>2016-04-01</p> <p>Located near Graz at the SE-rim of the Alps Katerloch is well-known for its impressive dripstone decoration, e.g. several metres tall and relatively fast growing (0.2-0.7 mm/yr on average) candle-stick-type stalagmites. In the course of an ongoing multi-annual and partially high-resolution cave monitoring program we study modern (active) sites of carbonate deposition focusing on the site-specific growth dynamics and connection of modern regional and cave environmental conditions with petrographic, chemical and stable isotopic information captured in the speleothems. Fresh <span class="hlt">calcite</span> precipitates on artificial (glass) substrates underneath active drip sites were collected continuously from 2006 to 2014 (eight years!). The samples (up to 7 mm thick) represent cave sections of different temperature and drip sites of partially different characteristics (e.g. drip rate). We also recovered short drill cores (up to 3 cm length, 1 cm diameter) from the top of active stalagmites probably representing the last decades to centuries of <span class="hlt">calcite</span> <span class="hlt">crystallization</span>. Moreover, an actively growing stalagmite (K10) comprising both modern and past <span class="hlt">calcite</span> deposition was collected. 238U-234U-230Th dating using MC-ICP-MS of K10 (71 cm long) revealed several distinct growth intervals (separated by growth interruptions) starting at 129.1 ±1.2 kyr BP (Last Interglacial) up to now, mostly reflecting warm and humid climate intervals. High-resolution (100 μm) isotope profiles micromilled from the multi-annual modern <span class="hlt">calcite</span> precipitates on artificial substrates revealed low δ13C values of -12.8 to -8.3 ‰ (VPDB) and relatively high δ18O of -6.9 to -4.9 ‰Ṫhe δ18O curves from all collection sites (different growth rate) record a pronounced decrease during their most recent growth period most likely corresponding to a significant decrease towards lower oxygen isotope values observed in drip waters collected in the year 2014 compared with samples from 2005 to 2007. Drip water δ2H /δ18O</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/publication/?seqNo115=245683','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/publication/?seqNo115=245683"><span><span class="hlt">Seed</span> Germination</span></a></p> <p><a target="_blank" href="http://www.ars.usda.gov/services/TekTran.htm">Technology Transfer Automated Retrieval System (TEKTRAN)</a></p> <p></p> <p></p> <p>Initiation of <span class="hlt">seed</span> germination is a critical decision for plants. It is important for <span class="hlt">seed</span> populations under natural conditions to spread the timing of germination of individual <span class="hlt">seeds</span> to maximize the probability of species survival. Therefore, <span class="hlt">seeds</span> have evolved the multiple layers of mechanisms tha...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V21B3036M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V21B3036M"><span>Controls on <span class="hlt">Calcite</span> Solubility in Metamorphic and Magmatic Fluids</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Manning, C. E.; Eguchi, J.; Galvez, M.</p> <p>2015-12-01</p> <p><span class="hlt">Calcite</span> is an important hydrothermal alteration product in a wide range of environments. The role of <span class="hlt">calcite</span> in hydrothermal alteration depends on its solubility in geologic fluids, especially H2O. At ambient T and P, <span class="hlt">calcite</span> solubility is low and it exhibits well-known declining, or "reverse", solubility with rising T. However, experimental and theoretical studies show that increasing P yields higher solubility and restricts the region of reverse solubility behavior to higher temperature. At 0.2 GPa the reverse solubility region lies at T>600°C; at 0.5 GPa, >800°C. Thus, whereas <span class="hlt">calcite</span> possesses relatively low solubility in pure H2O in shallow hydrothermal systems (typically <10 ppm C), it is substantially more soluble at conditions of middle and lower crustal metamorphism and magmatism, reaching concentrations ≥1000 ppm. At the higher P of subduction zones, aragonite solubility in H2O is even greater. Thus, neglecting other solubility controls, <span class="hlt">calcite</span> precipitation is favored as crustal fluids cool and/or decompress. However, the solubility of <span class="hlt">calcite</span> in H2O also depends strongly on other solutes, pH, and fO2. Sources of alkalinity decrease <span class="hlt">calcite</span> solubility. In contrast, sources of acidity such as CO2 and Cl increase solubility. Crustal fluids can be enriched in alkali halides such as NaCl. <span class="hlt">Calcite</span> solubility increases with increasing salt content at a given P and T. From approximately seawater salinity to salt saturation, the fluid behaves as a dilute molten salt and <span class="hlt">calcite</span> solubility increases as the square of the salt mole fraction regardless of the alkali (Li, Na, K, Cs) or halogen (F, Cl, Br, I) considered. Similar behavior is seen in mixed salt solutions. At lower salinities, solubility behavior is as expected in dilute electrolyte solutions. The transition from dilute electrolyte to molten salt is fundamental to the properties of crustal fluids. Reduction of carbonate species or CO2 in the fluid to CH4, which is common during serpentinization of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/12399694','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/12399694"><span>Defluoridation of drinking water by boiling with brushite and <span class="hlt">calcite</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Larsen, M J; Pearce, E I F</p> <p>2002-01-01</p> <p>Existing methods for defluoridating drinking water involve expensive high technology or are slow, inefficient and/or unhygienic. A new method is now suggested, encompassing brushite and <span class="hlt">calcite</span> suspension followed by boiling. Our aim was to examine the efficiency of the method and the chemical reactions involved. Brushite, 0.3-0.5 g, and an equal weight of <span class="hlt">calcite</span> were suspended in 1 litre water containing 5-20 ppm fluoride. The suspensions were boiled in an electric kettle, left to cool and the calcium salts to sediment. Solution ion concentrations were determined and sediments were examined by X-ray diffraction. In distilled water initially containing 5, 10 and 20 ppm fluoride the concentration was reduced to 0.06, 0.4 and 5.9 ppm, respectively. Using Aarhus tap water which contained 2.6 mmol/l calcium the final concentrations were 1.2, 2.5 and 7.7 ppm, respectively, and runs without <span class="hlt">calcite</span> gave results similar to those with <span class="hlt">calcite</span>. Without boiling the fluoride concentration remained unaltered, as did the brushite and <span class="hlt">calcite</span> salts, despite occasional agitation by hand. All solutions were supersaturated with respect to fluorapatite and hydroxyapatite and close to saturation with respect to brushite. Boiling produced well-crystallised apatite and traces of <span class="hlt">calcite</span>, while boiling of brushite alone left a poorly crystallised apatite. We conclude that boiling a brushite/<span class="hlt">calcite</span> suspension rapidly converts the two salts to apatite which incorporates fluoride if present in solution, and that this process may be exploited to defluoridate drinking water.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.B53D0700N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.B53D0700N"><span>The Thermodynamics Of <span class="hlt">Calcite</span> Nucleation On Organic Surfaces: Classical Vs. Non-Classical Pathways</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nielsen, M.; Hu, Q.; Hamm, L. M.; Lee, J. R.; Becker, U.; Dove, P. M.; De Yoreo, J.</p> <p>2012-12-01</p> <p>Nucleation in the natural world often occurs at organic surfaces. During biomineralization, living organisms use macromolecular matrices to direct nucleation of a variety of inorganic materials by controlling the timing, polymorphism, morphology, and crystallographic orientation of mineral nuclei. In geochemical settings, mineral surfaces, which are often covered with organic layers or biofilms, surround the volume within which nucleation occurs. Despite the importance of nucleation phenomena in these natural settings, our understanding of the reaction dynamics and energetics of the process is limited. Issues such as the role of pre-nucleation clusters, formation of amorphous precursors, and polymorph selection during the initial stages of nucleation, as well as the structural relationships between the organic matrix and the emerging nucleus are poorly understood. Using self-assembled monolayers (SAMs) of alkanethiols as simple models for macromolecular matrices and organic films, we address the gaps in our understanding by employing a suite of in situ methods to investigate CaCO3 nucleation. From optical measurements of <span class="hlt">calcite</span> nucleation rates on alkanethiol SAMs, we find that for two carboxyl-terminated alkanethiol SAMs with odd (mercaptoundecanoic acid) and even (mercaptohexadecanoic acid) carbon chains, the rate exhibits the supersaturation dependence expected from classical theory and the effective interfacial energy is reduced from about 109 mJ/m2 in bulk solution to 81 mJ/m2 and 72 mJ/m2, respectively. Theoretical analysis shows that the corresponding free energy barrier is reduced from 105kT for homogeneous nucleation in bulk solution to 27KT and 19kT, respectively. The results demonstrate that <span class="hlt">calcite</span> nucleation on these carboxyl SAMs is described well in purely classical terms through a reduction in the thermodynamic barrier due to decreased interfacial free energy. In addition, although amorphous particles form prior to <span class="hlt">crystal</span> nucleation on hydroxyl</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003GeCoA..67.3859P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003GeCoA..67.3859P"><span>Uptake of dissolved Cd by biogenic and abiogenic aragonite: a comparison with sorption onto <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Prieto, Manuel; Cubillas, Pablo; Fernández-Gonzalez, Ángeles</p> <p>2003-10-01</p> <p>The uptake of Cd 2+ by aragonite and <span class="hlt">calcite</span> is investigated by combining macroscopic measurements with some qualitative sorption experiments performed in a hydrogel medium. Both biogenic and abiogenic aragonites were studied in order to evaluate the process on materials with different textures. Assuming that sorption occurs by surface precipitation of metal-bearing solids, the gel produces a drastic decrease in the nucleation density, which allows for the precipitation of crystallites that are large enough to be analysed by scanning electron microscopy and characterized by glancing-incidence X-ray techniques. The macroscopic study reveals that aragonite is a powerful sorbent for cadmium in aqueous environments. Microscopic observations indicate that cadmium is sorbed onto aragonite by surface precipitation of (Cd, Ca)CO 3 solid solutions with a <span class="hlt">calcite</span>-type structure. The precipitating individuals grow randomly oriented on the surface to reach sizes in the micrometre range. As a consequence, the concentration of cadmium in the aqueous solution decreases dramatically to values controlled by the low solubility of the cadmium-rich end member. This mechanism involves simultaneous dissolution-<span class="hlt">crystallization</span> and is the same for both abiogenic and biogenic aragonites, the only difference being a result of the higher specific surface area of the biogenic starting material. Long-term uptake of cadmium by <span class="hlt">calcite</span> occurs through a similar dissolution-<span class="hlt">crystallization</span> mechanism, the final outcome being virtually the same, that is, surface precipitation of (Cd,Ca)CO 3 solid solutions. In this case, however, substrate and precipitate are isostructural and the process occurs by oriented overgrowth of thin lamellar crystallites, which spread to quickly cover the surface by a layer a few nanometers thick. This epitaxial layer armors the substrate from further dissolution, so that the process stops when only a small amount of cadmium has been removed from the fluid. As a result</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JCrGr.419...79N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JCrGr.419...79N"><span>Photoinduced synthesis of single-digit micrometer-size spheroidal <span class="hlt">calcite</span> composites in the presence of partially hydrolyzed poly(vinyl alcohol)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nishio, Takashi; Naka, Kensuke</p> <p>2015-06-01</p> <p>Photoinduced <span class="hlt">crystallization</span> of calcium carbonate (CaCO3), which was based on the photodecarboxylation of ketoprofen (KP, 2-(3-benzoylphyenyl)propionic acid) under alkaline conditions of pH 8.4 and 10 was studied for preparation of CaCO3 composite particles in single-digit micrometer-sizes. In this method, a homogeneous solution comprising KP, calcium chloride, ammonia, and partially hydrolyzed poly(vinyl alcohol) (PVAPS, degree of saponification: 86.5-89.0 mol%) was used as a precursor solution and was exposed to ultraviolet (UV) irradiation for different time periods. After the UV irradiation for 50 min, <span class="hlt">calcite</span> spheroids in single-digit micrometer-sizes were obtained as major products at pH 8.4. The obtained <span class="hlt">calcite</span> spheroids contained organic components of about 10 wt%. The comparison of the characteristics of the CaCO3 obtained at pH 8.4 and 10 suggests that the nucleation and <span class="hlt">crystallization</span> of both vaterite and <span class="hlt">calcite</span> continuously took place in a moderated supersaturation owing to the CO2 hydration equilibrium as long as the photodecarboxylation of KP continued. Consequently, the aggregation-based <span class="hlt">crystal</span> growth in the presence of PVAPS seemed to enable the formation of the spheroidal composites of <span class="hlt">calcite</span> in single-digit micrometer-sizes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4334277','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4334277"><span>Effect of Otoconial Proteins Fetuin A, Osteopontin, and Otoconin 90 on the Nucleation and Growth of <span class="hlt">Calcite</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p></p> <p>2015-01-01</p> <p>We investigated the roles of three proteins associated with the formation of otoconia including fetuin A, osteopontin (OPN), and otoconin 90 (OC90). In situ atomic force microscopy (AFM) studies of the effects of these proteins on the growth of atomic steps on <span class="hlt">calcite</span> surfaces were performed to obtain insight into their effects on the growth kinetics. We also used scanning electron microscopy to examine the effects of these proteins on <span class="hlt">crystal</span> morphology. All three proteins were found to be potent inhibitors of <span class="hlt">calcite</span> growth, although fetuin A promoted growth at concentrations below about 40 nM and only became an inhibitor at higher concentrations. We then used in situ optical microscopy to observe <span class="hlt">calcite</span> nucleation on films of these proteins adsorbed onto mica surfaces. By measuring the <span class="hlt">calcite</span> nucleation rate as a function of supersaturation, the value of the interfacial energy that controls the free energy barrier to heterogeneous nucleation was determined for each protein. OPN and OC90 films led to significantly reduced interfacial energies as compared to the value for homogeneous <span class="hlt">calcite</span> nucleation in bulk solution. The value for fetuin A was equal to that for bulk solution within experimental error. Zeta potential measurements showed all of the proteins possessed negative surface charge and varied in magnitude according to sequence fetuin A > OC90 > OPN. In addition, the interfacial energies exhibited an inverse scaling with the zeta potential. In analogy to previous measurements on polysaccharide films, this scaling indicates the differences between the proteins arise from the effect of protein surface charge on the solution–substrate interfacial energy. PMID:25709560</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1257637-effect-otoconial-proteins-fetuin-osteopontin-otoconin-nucleation-growth-calcite','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1257637-effect-otoconial-proteins-fetuin-osteopontin-otoconin-nucleation-growth-calcite"><span>Effect of otoconial proteins fetuin A, osteopontin, and otoconin 90 on the nucleation and growth of <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Hong, Mina; Moreland, K. Trent; Chen, Jiajun; ...</p> <p>2014-10-30</p> <p>Here, we investigated the roles of three proteins associated with the formation of otoconia including fetuin A, osteopontin (OPN), and otoconin 90 (OC90). In situ atomic force microscopy (AFM) studies of the effects of these proteins on the growth of atomic steps on <span class="hlt">calcite</span> surfaces were performed to obtain insight into their effects on the growth kinetics. We also used scanning electron microscopy to examine the effects of these proteins on <span class="hlt">crystal</span> morphology. All three proteins were found to be potent inhibitors of <span class="hlt">calcite</span> growth, although fetuin A promoted growth at concentrations below about 40 nM and only became anmore » inhibitor at higher concentrations. We then used in situ optical microscopy to observe <span class="hlt">calcite</span> nucleation on films of these proteins adsorbed onto mica surfaces. By measuring the <span class="hlt">calcite</span> nucleation rate as a function of supersaturation, the value of the interfacial energy that controls the free energy barrier to heterogeneous nucleation was determined for each protein. OPN and OC90 films led to significantly reduced interfacial energies as compared to the value for homogeneous <span class="hlt">calcite</span> nucleation in bulk solution. The value for fetuin A was equal to that for bulk solution within experimental error. Zeta potential measurements showed all of the proteins possessed negative surface charge and varied in magnitude according to sequence fetuin A > OC90 > OPN. In addition, the interfacial energies exhibited an inverse scaling with the zeta potential. In analogy to previous measurements on polysaccharide films, this scaling indicates the differences between the proteins arise from the effect of protein surface charge on the solution–substrate interfacial energy.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1257637','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1257637"><span>Effect of otoconial proteins fetuin A, osteopontin, and otoconin 90 on the nucleation and growth of <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hong, Mina; Moreland, K. Trent; Chen, Jiajun; Teng, Henry H.; Thalmann, Ruediger; De Yoreo, James J.</p> <p>2014-10-30</p> <p>Here, we investigated the roles of three proteins associated with the formation of otoconia including fetuin A, osteopontin (OPN), and otoconin 90 (OC90). In situ atomic force microscopy (AFM) studies of the effects of these proteins on the growth of atomic steps on <span class="hlt">calcite</span> surfaces were performed to obtain insight into their effects on the growth kinetics. We also used scanning electron microscopy to examine the effects of these proteins on <span class="hlt">crystal</span> morphology. All three proteins were found to be potent inhibitors of <span class="hlt">calcite</span> growth, although fetuin A promoted growth at concentrations below about 40 nM and only became an inhibitor at higher concentrations. We then used in situ optical microscopy to observe <span class="hlt">calcite</span> nucleation on films of these proteins adsorbed onto mica surfaces. By measuring the <span class="hlt">calcite</span> nucleation rate as a function of supersaturation, the value of the interfacial energy that controls the free energy barrier to heterogeneous nucleation was determined for each protein. OPN and OC90 films led to significantly reduced interfacial energies as compared to the value for homogeneous <span class="hlt">calcite</span> nucleation in bulk solution. The value for fetuin A was equal to that for bulk solution within experimental error. Zeta potential measurements showed all of the proteins possessed negative surface charge and varied in magnitude according to sequence fetuin A > OC90 > OPN. In addition, the interfacial energies exhibited an inverse scaling with the zeta potential. In analogy to previous measurements on polysaccharide films, this scaling indicates the differences between the proteins arise from the effect of protein surface charge on the solution–substrate interfacial energy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22253024','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22253024"><span>The Raman spectrum of CaCO{sub 3} polymorphs <span class="hlt">calcite</span> and aragonite: A combined experimental and computational study</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>De La Pierre, Marco E-mail: marco.delapierre@unito.it; Maschio, Lorenzo; Orlando, Roberto; Dovesi, Roberto; Carteret, Cédric E-mail: marco.delapierre@unito.it; André, Erwan</p> <p>2014-04-28</p> <p>Powder and single <span class="hlt">crystal</span> Raman spectra of the two most common phases of calcium carbonate are calculated with ab initio techniques (using a “hybrid” functional and a Gaussian-type basis set) and measured both at 80 K and room temperature. Frequencies of the Raman modes are in very good agreement between calculations and experiments: the mean absolute deviation at 80 K is 4 and 8 cm{sup −1} for <span class="hlt">calcite</span> and aragonite, respectively. As regards intensities, the agreement is in general good, although the computed values overestimate the measured ones in many cases. The combined analysis permits to identify almost all the fundamental experimental Raman peaks of the two compounds, with the exception of either modes with zero computed intensity or modes overlapping with more intense peaks. Additional peaks have been identified in both <span class="hlt">calcite</span> and aragonite, which have been assigned to {sup 18}O satellite modes or overtones. The agreement between the computed and measured spectra is quite satisfactory; in particular, simulation permits to clearly distinguish between <span class="hlt">calcite</span> and aragonite in the case of powder spectra, and among different polarization directions of each compound in the case of single <span class="hlt">crystal</span> spectra.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3677451','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3677451"><span>Polysaccharide chemistry regulates kinetics of <span class="hlt">calcite</span> nucleation through competition of interfacial energies</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Hamm, Laura M.; Han, Nizhou; De Yoreo, James J.; Dove, Patricia M.</p> <p>2013-01-01</p> <p>Calcified skeletons are produced within complex assemblages of proteins and polysaccharides whose roles in mineralization are not well understood. Here we quantify the kinetics of <span class="hlt">calcite</span> nucleation onto a suite of high-purity polysaccharide (PS) substrates under controlled conditions. The energy barriers to nucleation are PS-specific by a systematic relationship to PS charge density and substrate structure that is rooted in minimization of the competing substrate–<span class="hlt">crystal</span> and substrate–liquid interfacial energies. Chitosan presents a low-energy barrier to nucleation because its near-neutral charge favors formation of a substrate–<span class="hlt">crystal</span> interface, thus reducing substrate interactions with water. Progressively higher barriers are measured for negatively charged alginates and heparin that favor contact with the solution over the formation of new substrate–<span class="hlt">crystal</span> interfaces. The findings support a directing role for PS in biomineral formation and demonstrate that substrate–<span class="hlt">crystal</span> interactions are one end-member in a larger continuum of competing forces that regulate heterogeneous <span class="hlt">crystal</span> nucleation. PMID:23690577</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFM.B21G..08D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFM.B21G..08D"><span><span class="hlt">Calcite</span> and Picocyanobacteria in Lakes: Factors Affecting Their Interaction</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dittrich, M.; Obst, M.; Mavrocordatos, D.</p> <p>2003-12-01</p> <p><span class="hlt">Calcites</span> build large deposits which have been observed in the rock record throughout geological time at various localities around the globe. Carbonate deposits have affected atmospheric carbon dioxide concentration. As it has been generally accepted, inorganic precipitation represents a source of carbon dioxide on short geological time scales and a sink of inorganic carbon at long time scales from millions to thousands of millions years. However, recent research indicates that <span class="hlt">calcite</span> deposits may result from microbial calcification instead of inorganic precipitation. In this case the process may reduce atmospheric carbon dioxide on geologically short time scales. Thus the effect of carbonate sediment deposition on global carbon cycling depends on the origin of carbonate. Thus it is essential to understand the cause and the key parameters affecting <span class="hlt">calcite</span> precipitation. The role of algae and bacteria in <span class="hlt">calcite</span> formation in lakes has not been evaluated in detail. Some evidence, however, exists supporting precipitation of calcium carbonate by microbes as the origin of whiting. Several field studies on lakes have also produced puzzling results: The peaks of algal blooms were often not found at the same time as precipitation events of <span class="hlt">calcite</span>. We suspect that parts of the discrepancies in the interpretation of field observations are due to the activity of autotrophic picoplankton. The unicellular autotrophic picoplankton (APP) is a ubiquitous component of pelagic ecosystems. But it has often been overlooked due to its small cell size of 0.2 - 2 μ m in diameter. Coccoid picocyanobacteria of the Synechococcus-type dominate the picoplankton community in most oligotrophic systems. Recently, laboratory experiments and field observations suggested that APP may play an important role in <span class="hlt">calcite</span> precipitation. The aim of this study was to examine the influence of environmental factors such as saturation state, concentration of different dissolved ions and characteristics of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeCoA.192...70R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeCoA.192...70R"><span>Hydrochemical controls on aragonite versus <span class="hlt">calcite</span> precipitation in cave dripwaters</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rossi, Carlos; Lozano, Rafael P.</p> <p>2016-11-01</p> <p>Despite the paleoclimatic relevance of primary <span class="hlt">calcite</span> to aragonite transitions in stalagmites, the relative role of fluid Mg/Ca ratio, supersaturation and CO32- concentration in controlling such transitions is still incompletely understood. Accordingly, we have monitored the hydrochemistry of 50 drips and 8 pools that are currently precipitating <span class="hlt">calcite</span> and/or aragonite in El Soplao and Torca Ancha Caves (N. Spain), investigating the mineralogy and geochemistry of the CaCO3 precipitates on the corresponding natural speleothem surfaces. The data reveal that, apart from possible substrate effects, dripwater Mg/Ca is the only obvious control on CaCO3 polymorphism in the studied stalagmites and pools, where <span class="hlt">calcite</span>- and aragonite-precipitating dripwaters are separated by an initial (i.e. at stalactite tips) Mg/Ca threshold at ≈1.1 mol/mol. Within the analyzed ranges of pH (8.2-8.6), CO32- concentration (1-6 mg/L), supersaturation (SIaragonite: 0.08-1.08; SIcalcite: 0.23-1.24), drip rate (0.2-81 drops/min) and dissolved Zn (6-90 μg/L), we observe no unequivocal influence of these parameters on CaCO3 mineralogy. Despite the almost complete overlapping supersaturations of <span class="hlt">calcite</span>- and aragonite-precipitating waters, the latter are on average less supersaturated because the waters having Mg/Ca above ∼1.1 have mostly achieved such high ratios by previously precipitating <span class="hlt">calcite</span>. Both <span class="hlt">calcite</span> and aragonite precipitated at or near oxygen isotopic equilibrium, and Mg incorporation into <span class="hlt">calcite</span> was consistent with literature-based predictions, indicating that in the studied cases CaCO3 precipitation was not significantly influenced by strong kinetic effects. In the studied cases, the <span class="hlt">calcites</span> that precipitate at ∼11 °C from dripwaters with initial Mg/Ca approaching ∼1.1 incorporate ∼5 mol% MgCO3, close to the published value above which <span class="hlt">calcite</span> solubility exceeds aragonite solubility, suggesting that aragonite precipitation in high-relative-humidity caves is</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1065524','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1065524"><span>Surface kinetic model for isotopic and trace element fractionation during precipitation of <span class="hlt">calcite</span> from aqueous solution</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>DePaolo, Donald J.</p> <p>2011-01-01</p> <p>A surface reaction kinetic model is developed for predicting Ca isotope fractionation and metal/Ca ratios of <span class="hlt">calcite</span> as a function of rate of precipitation from aqueous solution. The model is based on the requirements for dynamic equilibrium; i.e. proximity to equilibrium conditions is determined by the ratio of the net precipitation rate (R<sub>p</sub>) to the gross forward precipitation rate (R<sub>f</sub>), for conditions where ionic transport to the growing <span class="hlt">crystal</span> surface is not rate-limiting. The value of R<sub>p</sub> has been experimentally measured under varying conditions, but the magnitude of R<sub>f</sub> is not generally known, and may depend on several factors. It is posited that, for systems with no trace constituents that alter the surface chemistry, R<sub>f</sub> can be estimated from the bulk far-from-equilibrium dissolution rate of <span class="hlt">calcite</span> (R<sub>b</sub> or k<sub>b</sub>), since at equilibrium R<sub>f </sub>= R<sub>b</sub>, and R<sub>p</sub> = 0. Hence it can be inferred that R<sub>f</sub> ≈ R<sub>p</sub> + R<sub>b</sub>. The dissolution rate of pure <span class="hlt">calcite</span> is measureable and is known to be a function of temperature and pH. At given temperature and pH, equilibrium precipitation is approached when R<sub>p</sub> (=R<sub>f</sub> - R<sub>b</sub>) « R<sub>b</sub>. For precipitation rates high enough that R<sub>p</sub> » R<sub>b</sub>, both isotopic and trace element partitioning are controlled by the kinetics of ion attachment to the mineral surface, which tend to favor more rapid incorporation of the light isotopes of Ca and discriminate weakly between trace metals and Ca. With varying precipitation rate, a transition region between equilibrium and kinetic control occurs near R<sub>p</sub> ≈ R<sub>b</sub> for Ca isotopic fractionation. According to this model, Ca isotopic data can be used to estimate R<sub>f</sub> for <span class="hlt">calcite</span> precipitation. Mechanistic models for <span class="hlt">calcite</span> precipitation indicate that the molecular exchange rate is not constant</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1005174','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1005174"><span>Surface kinetic model for isotopic and trace element fractionation during precipitation of <span class="hlt">calcite</span> from aqueous solution</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>DePaolo, D.</p> <p>2010-10-15</p> <p>A surface reaction kinetic model is developed for predicting Ca isotope fractionation and metal/Ca ratios of <span class="hlt">calcite</span> as a function of rate of precipitation from aqueous solution. The model is based on the requirements for dynamic equilibrium; i.e. proximity to equilibrium conditions is determined by the ratio of the net precipitation rate (R{sub p}) to the gross forward precipitation rate (R{sub f}), for conditions where ionic transport to the growing <span class="hlt">crystal</span> surface is not rate-limiting. The value of R{sub p} has been experimentally measured under varying conditions, but the magnitude of R{sub f} is not generally known, and may depend on several factors. It is posited that, for systems with no trace constituents that alter the surface chemistry, R{sub f} can be estimated from the bulk far-from-equilibrium dissolution rate of <span class="hlt">calcite</span> (R{sub b} or k{sub b}), since at equilibrium R{sub f} = R{sub b}, and R{sub p} = 0. Hence it can be inferred that R{sub f} {approx} R{sub p} + R{sub b}. The dissolution rate of pure <span class="hlt">calcite</span> is measureable and is known to be a function of temperature and pH. At given temperature and pH, equilibrium precipitation is approached when R{sub p} (= R{sub f} - R{sub b}) << R{sub b}. For precipitation rates high enough that R{sub p} >> R{sub b}, both isotopic and trace element partitioning are controlled by the kinetics of ion attachment to the mineral surface, which tend to favor more rapid incorporation of the light isotopes of Ca and discriminate weakly between trace metals and Ca. With varying precipitation rate, a transition region between equilibrium and kinetic control occurs near R{sub p} {approx} R{sub b} for Ca isotopic fractionation. According to this model, Ca isotopic data can be used to estimate R{sub f} for <span class="hlt">calcite</span> precipitation. Mechanistic models for <span class="hlt">calcite</span> precipitation indicate that the molecular exchange rate is not constant at constant T and pH, but rather is dependent also on solution saturation state and hence R{sub p</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AcSpA.117..158S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AcSpA.117..158S"><span>A Raman spectroscopic comparison of <span class="hlt">calcite</span> and dolomite</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sun, Junmin; Wu, Zeguang; Cheng, Hongfei; Zhang, Zhanjun; Frost, Ray L.</p> <p>2014-01-01</p> <p>Raman spectroscopy was used to characterize and differentiate the two minerals <span class="hlt">calcite</span> and dolomite and the bands related to the mineral structure. The (CO3)2- group is characterized by four prominent Raman vibrational modes: (a) the symmetric stretching, (b) the asymmetric deformation, (c) asymmetric stretching and (d) symmetric deformation. These vibrational modes of the <span class="hlt">calcite</span> and dolomite were observed at 1440, 1088, 715 and 278 cm-1. The significant differences between the minerals <span class="hlt">calcite</span> and dolomite are observed by Raman spectroscopy. <span class="hlt">Calcite</span> shows the typical bands observed at 1361, 1047, 715 and 157 cm-1, and the special bands at 1393, 1098, 1069, 1019, 299, 258 and 176 cm-1 for dolomite are observed. The difference is explained on the basis of the structure variation of the two minerals. <span class="hlt">Calcite</span> has a trigonal structure with two molecules per unit cell, and dolomite has a hexagonal structure. This is more likely to cause the splitting and distorting of the carbonate groups. Another cause for the difference is the cation substituting for Mg in the dolomite mineral.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23988531','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23988531"><span>A Raman spectroscopic comparison of <span class="hlt">calcite</span> and dolomite.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Sun, Junmin; Wu, Zeguang; Cheng, Hongfei; Zhang, Zhanjun; Frost, Ray L</p> <p>2014-01-03</p> <p>Raman spectroscopy was used to characterize and differentiate the two minerals <span class="hlt">calcite</span> and dolomite and the bands related to the mineral structure. The (CO3)(2-) group is characterized by four prominent Raman vibrational modes: (a) the symmetric stretching, (b) the asymmetric deformation, (c) asymmetric stretching and (d) symmetric deformation. These vibrational modes of the <span class="hlt">calcite</span> and dolomite were observed at 1440, 1088, 715 and 278 cm(-1). The significant differences between the minerals <span class="hlt">calcite</span> and dolomite are observed by Raman spectroscopy. <span class="hlt">Calcite</span> shows the typical bands observed at 1361, 1047, 715 and 157 cm(-1), and the special bands at 1393, 1098, 1069, 1019, 299, 258 and 176 cm(-1) for dolomite are observed. The difference is explained on the basis of the structure variation of the two minerals. <span class="hlt">Calcite</span> has a trigonal structure with two molecules per unit cell, and dolomite has a hexagonal structure. This is more likely to cause the splitting and distorting of the carbonate groups. Another cause for the difference is the cation substituting for Mg in the dolomite mineral.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/20003897','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/20003897"><span>Novel TEM approaches to imaging of microstructures in carbonates: Clues to growth mechanisms in <span class="hlt">calcite</span> and dolomite</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Paquette, J.; Vali, H.; Mountjoy, E.</p> <p>1999-12-01</p> <p>Relating microstructures imaged by transmission electron microscopy (TEM) to specific growth mechanisms requires imaging of both the surface microtopography on <span class="hlt">crystal</span> faces and its corresponding microstructure in the bulk <span class="hlt">crystal</span>. Pt-C replicas of as-grown surfaces are ideally suited to this task, as they provide a high-resolution, nearly three-dimensional image of surface topography that can be correlated with microstructures visible in sections at high angle to the as-grown surface. Ultramicrotomy enables the preparation of ultrathin sections more quickly than conventional ion-thinning and can be used to investigate chemical heterogeneities by analytical electron microscopy (AEM). The authors evaluate the potential of both techniques for the study of microstructures in <span class="hlt">calcite</span> and dolomite. (1) TEM images were obtained from Pt-C replicas of synthetic <span class="hlt">calcite</span>. The as-grown (10{bar 1}4) face of a Mg/Mn-doped <span class="hlt">crystal</span> growth showed growth hillocks aligned along preferred orientations. In Pb/Mn/Sr-doped <span class="hlt">calcite</span>, sections at high angle to as-grown faces showed a uniform microstructure in {l{underscore}brace}10{bar 1}4{r{underscore}brace} sectors. The {l{underscore}brace}01{bar 1}2{r{underscore}brace} sectors contained concentric zones that alternated from striated to uniform microstructures, suggesting periodic variations in growth rate and possibly in the growth mechanism. An oscillatory-zoned Mn-doped <span class="hlt">calcite</span> showed fine-scale banding (30--150 mm) and periodic roughening of (10{bar 1}4) surfaces that suggest repetitive transitions between growth mechanisms.(2) In sedimentary dolomites, Pt-C replicas of surfaces cleaved parallel to a (10{bar 1}4) face showed a hillocky topography or smooth (10{bar 1}4) surfaces modified by non-equivalent facets. Surfaces produced by cleavage at high angle to a (10{bar 1}4) face exposed sectors with fine-scale banding crosscut by sharp boundaries, suggestive of closely spaced growth hillocks intercalated with non-equivalent subsectors</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.B41B0027B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.B41B0027B"><span>Geochemical Proxy Distribution at the Atomic-Scale: Atom Probe Tomography of Foraminiferal <span class="hlt">Calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Branson, O.; Perea, D. E.; Winters, M. A.; Fehrenbacher, J. S.; Russell, A. D.; Spero, H. J.; Gagnon, A. C.</p> <p>2014-12-01</p> <p>Biomineral composition reflects a complex interplay between minute-scale biological control, mineral growth processes, and the influence of environmental conditions. For this reason, the mechanisms responsible for the formation of these minerals, as well as the incorporation of trace elements during biomineral growth, are poorly understood. Potential mechanisms governing the production and composition of biominerals can be organized into two distinct groups: a) biological mechanisms controlling the calcifying environment and b) mineral growth processes from this controlled environment. Despite significant advances in both these areas, critical gaps remain in our understanding of biomineral production and geochemical tracer incorporation. We are adapting Atom Probe Tomography (APT), a technique that maps the arrangement and identity of individual atoms within a bulk material, to analyze foraminiferal <span class="hlt">calcite</span> for the first time. These data-rich atom-scale chemical maps provide a unique opportunity to deconvolve the effects of biological and <span class="hlt">crystal</span> growth processes in the incorporation of geochemical tracers. Our first experiments have examined the influence of the biological-mineral interface on geochemical proxy element incorporation. Preliminary measurements show that (1) we can successfully map impurities in <span class="hlt">calcite</span> biominerals, while also distinguishing between mineral and organic zones, overcoming a major technical hurdle; and (2) that elements like sodium appear to be recruited to the organic-mineral interface. The high-resolution chemical data from the APT will further allow us to investigate the fundamental basis for geochemical proxy behavior. For example, we can determine for a certain set of conditions whether the substitution of trace elements into the <span class="hlt">calcite</span> follows ideal solid-solution behavior, as tacitly assumed in many geochemical proxy systems, or is modulated by intra-shell organics, or coupled-substitution interactions. Collectively, the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002GeCoA..66..927S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002GeCoA..66..927S"><span>Climate proxies from Sr/Ca of coccolith <span class="hlt">calcite</span>: calibrations from continuous culture of Emiliania huxleyi</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stoll, Heather M.; Rosenthal, Yair; Falkowski, Paul</p> <p>2002-03-01</p> <p>Continuous culture of the coccolithophorid Emiliania huxleyi reveals that coccolith Sr/Ca ratios depend on temperature and growth rate. At a constant temperature of 18°C, coccolith Sr/Ca ratios increased nearly 15% as growth rate increased from 0.1 to 1.5 divisions per day and calcification rate increased from 1.5 to 50 pg <span class="hlt">calcite</span> per cell per day. When temperature increased from 7 to 26°C, Sr/Ca ratios increased by more than 25% (i.e., 1%/1°C), although the range in growth and calcification rates was the same as for experiments at constant temperature. The temperature dependence of Sr/Ca ratios in coccoliths is consistent with that observed in planktonic foraminifera and abiogenic <span class="hlt">calcites</span>, suggesting that it is controlled by thermodynamic processes. However, the positive correlation of coccolith Sr/Ca with temperature contrasts with field studies in the equatorial Pacific, where Sr/Ca ratios are highest at the locus of maximum upwelling and productivity despite depressed temperatures. This paradox may reflect different calcification rate effects between E. huxleyi and the other species dominating assemblages in the equatorial Pacific sediments, which may be resolved by new techniques for separation of monospecific coccolith samples from sediments. Models of <span class="hlt">crystal</span> growth indicate that kinetic effects on Sr partitioning in <span class="hlt">calcite</span> due to surface enrichment could explain the Sr/Ca variations observed in constant temperature experiments but not the larger amplitude calcification rate effects observed in equatorial Pacific sediments. Despite the dual influence of temperature and growth rate on coccolith Sr/Ca, coccolith Sr/Ca correlates with "b," the slope of the dependence of carbon isotope fractionation in biomarkers (ɛ p) on CO 2(aq) at a range of growth rates and temperatures. Consequently, using coccolith Sr/Ca in combination with alkenone ɛ p may improve paleo-CO 2 determinations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/20026848','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/20026848"><span>Chemistry and kinetics of <span class="hlt">calcite</span> dissolution in passive treatment systems</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Rose, A.W.</p> <p>1999-07-01</p> <p>Reaction of <span class="hlt">calcite</span> with AMD is a key remediation process in anoxic limestone drains, (ALD), SAPS, and many wetlands, but predictions of effluent quality are currently based mainly on rules of thumb and prior experience. The PHREEQC computer program can be used to calculate the progress of this and similar reactions, and aid in understanding, design and evaluation of these systems. At pH values less than 5, <span class="hlt">calcite</span> dissolution rates are strongly influenced by transport parameters such as flow velocity. Estimated <span class="hlt">calcite</span> dissolution rates from ALD's and column experiments indicate little change in rate with pH, in contrast to published data for well stirred lab experiments. The dissolution rate is affected by concentration of SO{sub 4}, Fe, Al, Ca, P, and other trace solutes. The optimum contact time and sizing of ALD's will be dependent on these and possibly other parameters. Additional experiments are needed to evaluate these dependencies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1817255R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1817255R"><span>Small scale shear zone in <span class="hlt">calcite</span>: AMS and microstructure</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Roxerová, Zuzana; Machek, Matěj; Kusbach, Vladimír; Racek, Martin; Silva, Pedro F.</p> <p>2016-04-01</p> <p>Two structural profiles across thin shear zone in <span class="hlt">calcite</span> from quarry in Estremoz (Portugal) were studied to find a relationship between AMS and strain in natural rocks. The mesoscopic fabric is characterized by the change from the subhorizontal coarse-grained foliation towards the ~2cm-wide shear zone center with subvertical fine-grained foliation. In microstructure, the shear zone records dynamic recrystallization of <span class="hlt">calcite</span> aggregate which resulted in development of porphyroclastic microstructure with increasing proportion of fine-grained recrystallized matrix towards the shear zone center. Two distinct crystallographic preferred orientations of <span class="hlt">calcite</span> were recorded. One related with porphyroclasts, characterized by subvertical orientation of <span class="hlt">calcite</span> <c> axes and another associated with recrystallized matrix showing subhorizontal <span class="hlt">calcite</span> <c> axes orientation. The magnetic susceptibility ranges from -8e-6SI to 9e-6SI, with the average -4e-6SI. The majority of the rock mass is diamagnetic, corresponding well with the thermomagnetic curves, with local paramagnetic accumulations in form of thin bands. The AMS of the both profiles exhibits stable subvertical foliation bearing vertical lineation which is locally alternated by the medium-angle foliation. We interpret the AMS fabric pattern which is perpendicular to the mineral one as a type of inverse AMS fabric, due to high iron content in major part of <span class="hlt">calcite</span> grains The magnetic and microstructural description of the shear zone is accompanied by numerical modeling of AMS based on CPO and different proportion of porphyroclasts, matrix and mica for purposes of deciphering the influence of present microstructural features on AMS.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.H21A1051S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.H21A1051S"><span>Microbially Induced <span class="hlt">Calcite</span> Precipitation for Subsurface Immobilization of Contaminants</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smith, R. W.; Fujita, Y.; Ginn, T. R.; Hubbard, S. S.; Dafflon, B.; Delwiche, M.; Gebrehiwet, T.; Henriksen, J. R.; Peterson, J.; Taylor, J. L.</p> <p>2011-12-01</p> <p>Subsurface radionuclide and metal contaminants throughout the U.S. Department of Energy (DOE) complex pose one of the greatest challenges for long-term stewardship. One promising stabilization mechanism for divalent trace ions, such as the short-lived radionuclide 90Sr, is co-precipitation in <span class="hlt">calcite</span>. We have found that <span class="hlt">calcite</span> precipitation and co-precipitation of Sr can be accelerated by the activity of urea hydrolyzing microorganisms, that higher <span class="hlt">calcite</span> precipitation rates can result in increased Sr partitioning, and that nutrient additions can stimulate ureolytic activity. To extend our understanding of microbially induced <span class="hlt">calcite</span> precipitation (MICP) in an aquifer setting a continuous recirculation field experiment evaluating MICP was conducted at the Integrated Field Research Challenge (IFRC) site located at Rifle, CO. In this experiment, groundwater extracted from an onsite well was amended with urea (total mass of 42.5 kg) and molasses (a carbon and electron donor) and re-injected into a well approximately 4 meters up-gradient for a period of 12 days followed by 10 months of groundwater sampling and monitoring. Crosshole radar and electrical tomographic data were collected prior, during, and after the MICP treatment. The urea and molasses treatment resulted in an enhanced population of sediment associated urea hydrolyzing organisms as evidenced by increases in the number of ureC gene copies, increases in 14C urea hydrolysis rates, and long-term observations of ammonium (a urea hydrolysis product) in the injection, extraction and down gradient monitoring wells. Permeability changes and increases in the <span class="hlt">calcite</span> saturation indexes in the well field suggest that mineral precipitation has occurred; ongoing analysis of field samples seeks to confirm this. Changes in dielectric constant and electrical conductivity were used to interpret the spatiotemporal distribution of the injectate and subsequent <span class="hlt">calcite</span> precipitation. Modeling activities are underway to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeCoA.176..198A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeCoA.176..198A"><span>Is bicarbonate stable in and on the <span class="hlt">calcite</span> surface?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Andersson, M. P.; Rodriguez-Blanco, J. D.; Stipp, S. L. S.</p> <p>2016-03-01</p> <p>We have used density functional theory with the COSMO-RS implicit solvent model to predict the pKa for the deprotonation of bicarbonate to carbonate, i.e. HCO3- <=> CO32- + H+, when HCO3- is included in, and adsorbed on, a <span class="hlt">calcite</span> surface. We have used cluster models (80-100 atoms) to represent the flat {10.4} surface, acute steps, obtuse steps, two types of kinks on the acute step and two types of kinks on the obtuse steps. Based on the predicted pKa values, which range from -6.0 to 2.4 depending on the surface site, we conclude that bicarbonate deprotonates to carbonate when it is in <span class="hlt">calcite</span> even when pH in solution is very low. This is true for all surface sites, even for solutions where 2.4 < pH < 6.35, where H2CO30 is the dominant dissolved species. When bicarbonate is adsorbed on <span class="hlt">calcite</span>, the predicted pKa for deprotonation is 7.5, which is ∼3 pH units lower than in aqueous solution, 10.35. This means that adsorbed carbonate is stable even when the concentration of dissolved CO32- is several orders of magnitude lower. This has a significant effect on surface charge and thus the behaviour of the <span class="hlt">calcite</span> surface. Our results help explain the potential determining behaviour of the carbonate species in <span class="hlt">calcite</span>-water systems, particularly in the pH range where the bicarbonate species dominates in water and where the carbonate species dominates at the surface, i.e. when 7.5 < pH < 10.35. Our atomic scale data for the various <span class="hlt">calcite</span> surface sites provide the needed input to improve and constrain surface complexation modelling and are especially useful for predicting behaviour in systems where experiments are difficult or impossible, such as at high temperature and pressure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1995Geo....23..535D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1995Geo....23..535D"><span>Paleozoic Mg <span class="hlt">calcite</span> preserved: Implications for the Carboniferous ocean</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dickson, J. A. D.</p> <p>1995-06-01</p> <p>Modern Mg <span class="hlt">calcite</span> echinoderm skeletons are thought to lose Mg so rapidly that no pre-Pleistocene ossicles retain their original Mg concentrations; however, Carboniferous echinoderm skeletons from the Imo Formation of Arkansas and the Holder Formation of New Mexico are reported herein that are still composed of Mg <span class="hlt">calcite</span> (7.8 to 14.5 mol% MgCO3). Their Sr concentration is also high (620 to 3710 ppm). The pore system in these echinoderm skeletons is filled with ferroan <span class="hlt">calcite</span> or siderite that has not grown in optical continuity with the skeleton. The discovery of Carboniferous Mg <span class="hlt">calcite</span> confirms an interpretation already made from their diagenetic replacements. Marine Mg <span class="hlt">calcite</span> has been associated with proposed icehouse conditions, and although the Carboniferous echinoderm skeletons are compatible with this as they formed during Gondwana glaciation, they are too few to be of significance. Also they are organic secretions and so can override secular mineral trends based on inorganic precipitates. The Carboniferous echinoderm skeletons, produced in tropical waters, have a concentration of Mg similar to values for modern echinoderms. The simplest explanation for this similarity is that both precipitated by similar processes from oceans of similar composition. This does not support predictions, based on mass-balance modeling, that the Mg/Ca ratio of the Carboniferous ocean was half that of today's. The Sr content of Carboniferous echinoderms is less than that for modern echinoderms, leading to a prediction of 6 ppm Sr concentration for the Carboniferous ocean. Further examples of Mg <span class="hlt">calcite</span> are required to substantiate these interpretations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5880302','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5880302"><span>Radiaxial-fibrous <span class="hlt">calcites</span> of shallow subsurface diagenetic origin</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mazzullo, S.J.; Bischoff, W.D.; Lobitzer, H.</p> <p>1989-03-01</p> <p>Radiaxial-fibrous <span class="hlt">calcites</span> (RFC) in marine carbonates are generally considered syndepositional cements. In Upper Triassic and basal Liassic reef and platform limestones in Austria (Steinplatte complex), however, isopachous RFC is demonstrably a postdepositional diagenetic component that precipitated in shallow-burial phreatic environments during a time of periodic meteoric exposure. Isopachous RFC occurs solely within solution cavities and is interlayered with internal red sediment; discontinuities due to leaching separate sequential generations of RFC in the rocks. Accordingly, one possibility is that the RFC was originally low-magnesium <span class="hlt">calcite</span> that precipitated in the meteoric phreatic zone during lowstands. Such <span class="hlt">calcites</span> contain relatively low magnesium concentrations (average 0.87 mole % MgCO/sub 3/) and are /sup 18/O depleted (average - 5.81 /per thousand/ PDB). However, most other RFC cements in the sequence average slightly higher magnesium comparable to crinoidal <span class="hlt">calcites</span> (1.13 mole % MgCO/sub 3/), are less depleted in /sup 18/O (average - 1.88 /per thousand/ PDB), and are partly dolomitized. Additionally, all the RFC cements are enriched in /sup 13/C to values similar to that of Triassic and Jurassic seawater (+ 2.86 /per thousand/ PDB) and are nonluminescent. Trace element studies indicate alteration of the rocks in partly closed, rock-dominated diagenetic systems. By these facts, the authors favor a precursor high-magnesium <span class="hlt">calcite</span> mineralogy for the RFC cements, which possibly precipitated during highstands when meteoric pore waters were replaced by marine fluids. Thus, the geochemical trends observed are likely due to variations in the degree of meteoric alteration of high-magnesium <span class="hlt">calcite</span> RFC rather than to differences in original mineralogy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.4788M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.4788M"><span>Magnesium incorporation in <span class="hlt">calcite</span> in the presence of organic ligands</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mavromatis, Vasileios; Baldermann, Andre; Purgstaller, Bettina; Dietzel, Martin</p> <p>2015-04-01</p> <p>The formation of authigenic Mg-<span class="hlt">calcites</span> in marine early diagenetic environments is commonly driven by a bio-induced process, the anaerobic oxidation of methane (AOM), which provides inorganic carbon required for the precipitation of such authigenic carbonates. In such settings the availability of major and/or trace divalent metal cations (Me2+) incorporated in <span class="hlt">calcite</span> and their aqueous speciation are controlled by the presence of aqueous organic molecules that are produced either as (by-)products of biological activity (i.e. exopolymeric substances) or during degradation of allochthonous organic matter in the sediments. Despite the fact that the presence of aqueous organic ligands strongly affects the growth rates and the mineralogy of precipitating CaCO3 polymorphs, till now no study addresses the role of Me2+-ligand aqueous complexes on the extent of Mg and/or other trace element content of Mg-<span class="hlt">calcites</span>. In order to shed light on this process, relevant to authigenic <span class="hlt">calcite</span> formation in organic-rich marine sediments and continental soils, we precipitated <span class="hlt">calcite</span> in the presence of aqueous Mg and a variety of low molecular weight carboxylic- and aminoacids. Our experimental data indicate that the presence of organic ligands augments significantly the saturation state of <span class="hlt">calcite</span> in the parent fluid during its precipitation. Moreover, they suggest that the higher the ligand concentration, the higher the obtained distribution coefficient of Mg in <span class="hlt">calcite</span>. The latter is directly proportional to the ratio of Mg2+/Ca2+ aqueous ions for all ligands used. Hydrogeochemical modelling of the aqueous fluids indicate that the observed correlation can be explained by the stronger complexation of Ca2+ with organic ligands compared to Mg2+, which results in higher availability of Mg2+ vs. Ca2+ aqueous ions. Overall the obtained results suggest that the higher the organic ligand aqueous concentration the higher the Mg content of <span class="hlt">calcite</span> forming from this fluid. These findings are</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26067036','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26067036"><span>Structure and properties of Bi(Zn0.5Ti0.5)O3- Pb(Zr(1-x)Ti(x))O3 ferroelectric single <span class="hlt">crystals</span> grown by a top-<span class="hlt">seeded</span> solution growth technique.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wang, Bixia; Wu, Xiaoqing; Ren, Wei; Ye, Zuo-Guang</p> <p>2015-06-01</p> <p>Bi(Zn0.5Ti0.5)O3 (BZT)-modified Pb(Zr(1-x)Ti(x))O3 (PZT) single <span class="hlt">crystals</span> have been grown using a top-<span class="hlt">seeded</span> solution growth technique and characterized by various methods. The <span class="hlt">crystal</span> structure is found to be rhombohedral by means of X-ray powder diffraction. The composition and homogeneity of the as-grown single <span class="hlt">crystals</span> are studied by laser ablation inductively coupled plasma mass spectrometry and X-ray photoelectron spectroscopy. The domain structure of a (001)(cub) platelet is investigated by polarized light microscopy (PLM), which confirms the rhombohedral symmetry. The paraelectric-to-ferroelectric phase transition temperature T(C) is found to be 313°C with the absence of rhombohedral-tetragonal phase transition. The ferroelectric properties of the ternary <span class="hlt">crystals</span> are enhanced by the BZT substitution with a remanent polarization of 28 μC/cm(2) and a coercive field E(C) of 22.1 kV/cm.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6819502','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6819502"><span>Field test of a <span class="hlt">calcite</span> dissolution rate law: Fort's Funnel Cave, Mammoth Cave National Park</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Slunder, J.S. ); Groves, C.G. . Center for Cave and Karst Studies)</p> <p>1994-03-01</p> <p>The laboratory-derived <span class="hlt">calcite</span> dissolution rate law of Plummer et al. (1978) is the most widely used and mechanistically detailed expression currently available for predicting dissolution rates as a function of water chemistry. Such rate expressions are of great use in understanding timescales associated with limestone karst development. Little work has gone into the field testing of the rate law under natural conditions. This work measured dissolution rates by a <span class="hlt">crystal</span> weight loss experiment in Buffalo Creek within Fort's funnel Cave, which lies within a pristine, forested catchment of Mammoth Cave National Park. Continuous water chemistry sampling over the same period allowed a time-integrated prediction of the dissolution based on the Plummer et al. (1978) expression. Results indicate that the rate law overpredicted dissolution by a factor of about ten. This concurs with earlier laboratory work suggesting that the law tends to overpredict rates in solutions close to equilibrium with respect to <span class="hlt">calcite</span>, as were the waters within this part of the groundwater flow system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1712557N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1712557N"><span>Chalk-<span class="hlt">calcite</span>-microfluidic experiments: construction and flooding of microsystems with reactive fluids</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Neuville, Amélie; Thuy Luu, Thi; Dysthe, Dag Kristian; Vinningland, Jan Ludvig; Hiorth, Aksel</p> <p>2015-04-01</p> <p>Direct in situ observation of the pore structure changes that occur when chalk is flooded with brines could resolve many of the open questions that remain about the interactions between mineralogical alterations and oil-liberating mechanisms. Experiments on core scale and field tests that have been carried out the last decade have clearly shown that water chemistry affects the final oil recovery. However, there is generally no consensus in the scientific community of why additional oil is released. In this work, our aim is to focus on in-situ observations of single phase flow and interactions at the pore scale. To do so, we create several types of custom-made microsystems with chalk and <span class="hlt">calcite</span> <span class="hlt">crystals</span>. We then do experiments with reacting fluids in these microsystems. During these experiments, we realize in-situ observations (geometrical characteristics, reaction rate) using microsopy techniques (white light vertical/phase shift interferometric microscopy, and classical microscopy), and show how they vary as function as the water chemistry. In simple systems made of <span class="hlt">calcite</span>, we obtain reactive rates that are coherent with the litterature and with numerical simulations based on Lattice-Boltzmann methods.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24154609','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24154609"><span>Molecular tectonics: from <span class="hlt">crystals</span> to <span class="hlt">crystals</span> of <span class="hlt">crystals</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Marinescu, Gabriela; Ferlay, Sylvie; Kyritsakas, Nathalie; Hosseini, Mir Wais</p> <p>2013-12-11</p> <p>The in situ combination of M(II) cations (Co, Ni, Cu or Zn) with 2,4,6-pyridinetricarboxylic acid as a ligand, a bisamidinium dication as a H-bond donor tecton and NaOH leads to the formation of anionic metal complexes ML2(2-) and their interconnection into isomorphous 3D H-bonded networks displaying different colours which were used as preformed <span class="hlt">seed</span> <span class="hlt">crystals</span> for the formation of <span class="hlt">crystals</span> of <span class="hlt">crystals</span> by 3D epitaxial growth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.4829P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.4829P"><span>Inversion of <span class="hlt">calcite</span> twin data for stress (2) : EBSD as a tool for data measurements</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Parlangeau, Camille; Lacombe, Olivier; Brisset, Francois; Kohler, Eric; Daniel, Jean-Marc; Schueller, Sylvie</p> <p>2015-04-01</p> <p>Inversion of <span class="hlt">calcite</span> twin data are known to be a powerful tool to reconstruct the past state(s) of stress in carbonate rocks of the crust, especially in fold-and-thrust belts and sedimentary basins. Twin data measurements have been for long carried out optically using a Universal-Stage. This data collection is time-consuming and suffers from limitations and bias related to measurements of twin planes oblique at low angle or parallel to the thin section, or the unambiguous evaluation of the twinned/untwinned character of collected twin data. EBSD (electron backscatter diffraction) is a well-known technique applied to characterize textures and microstructures of metals or deformed fine-grained rocks. The challenge is to define a strategy for measuring <span class="hlt">calcite</span>-twin orientations that should be fast, without any loss of information, and which must reconcile (1) the need for a large amount of <span class="hlt">calcite</span> twin data (3 mutually perpendicular thin sections and at least 30 <span class="hlt">crystals</span> per thin section), (2) the spacing between EBSD spots, that should take into account (3) the small width of twin lamellae within grains deformed at low pressure and temperature and (4) the large size (usually several hundreds of microns) of twinned <span class="hlt">calcite</span> grains used for stress analysis. To date, these multiple requirements preclude any (classical) automatic twin data acquisition but instead imply a preliminary definition of the areas of the thin section to be scanned by the EBSD spots, including grain boundaries, because the stress inversion technique requires to know for each grain the orientations of the C axis and of the 3 potential e twin planes. In order to reconcile a perfectly polished surface as required by EBSD and the recognition of grain boundaries, we adopted the double etching technique (Herwegh, 2000) to first reveal grain and twin boundaries. Then, with a SEM and a very fine coating sample, the section is scanned using secondary electrons bin; each spot of interest is visually defined</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S11C4359S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S11C4359S"><span>Shock Waves Trigger Fault Weakening in <span class="hlt">Calcite</span>-bearing Rocks During Earthquakes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Spagnuolo, E.; Plumper, O.; Violay, M.; Cavallo, A.; Di Toro, G.</p> <p>2014-12-01</p> <p>The weakening mechanism of <span class="hlt">calcite</span>-bearing rocks is still poorly understood though many major earthquakes stroke within carbonate sequences. Insights derive from the laboratory: in experiments performed on <span class="hlt">calcite</span>-bearing gouges, up to 90% drop in friction is associated to grain size reduction to the nanoscale and the formation of <span class="hlt">crystal</span>-plastic microstructures suggesting the activation of debated weakening mechanisms (e.g., grain boundary sliding and diffusion creep; nanopowder lubrication). Whatever the case, it is unclear how nanoparticles form and what their role is at the initiation of sliding. To investigate initial fault instability we sheared with a rotary shear apparatus SHIVA pre-cut ring-shaped solid cylinders (50/30 mm ext/int diameter) of Carrara marble (99.9% CaCO3). Rock cylinders were slid for few millimetres(0, 1.5 mm and 5mm) at accelerations (6.5 ms-2) and normal stresses (10 MPa) approaching seismic deformation conditions. Initial slip (<2 mm) was concomitant with large frictional weakening (up to 30% of static friction) and CO2emission. Microanalytical observations (FE-SEM, FIB-SEM and TEM) showed that the experimental slipping zones consisted of (1) defects structures, including dislocations, cleavage surfaces and deformation features such as mechanical twins, partially burden beneath (2) a 2-10 micrometer thick layer of nanograins where pervasive nano-fracturing have occurred preserving the grain shape (pulverization) and (3) reaction products attributable to high pressure and high temperature conditions (i.e. <span class="hlt">calcite</span> decomposition into amorphous carbon rimming the nanograins). All the above features are typical of shock-induced changes in minerals. We interpret the above observations as follows: pre-existing grain boundaries or newly formed defects are the nuclei for the generation of dislocations and for their pile-up; the fast release of those piles-up in avalanches under rapid stress loading (fast moving dislocations) may explain the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMPP21C1917W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMPP21C1917W"><span>Origin of authigenic <span class="hlt">calcite</span> and aragonite in pelagic sediments of the Mendeleev Ridge (Arctic Ocean) and their paleoceanographicimplications</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Woo, K. S.; Ji, H. S.; Nam, S.; Stein, R. H.; Mackensen, A.; Matthiessen, J. J.</p> <p>2013-12-01</p> <p>Carbonate minerals were discovered from the giant box core (PS72/410-1) of the pelagic sediments recovered from the Canadian Arctic across the central Mendeleev Ridge (Station location= Lat. 80°30.37"N, Long. 175°44.38"W) during the Arctic cruise by Polarstern in 2008. The core was 39 cm long and was collected from the water depth of 1802 meters. The sediments show various colours from grey to brown as previously reported in other Arctic pelagic sediments. The sediments include planktonic foraminifers together with carbonate minerals. The contents of planktonic foraminifers and carbonate minerals vary with core depth, however these carbonate minerals are present through the whole sequence except for a few centimetres. After wet sieving, coarse fractions were texturally examined with binocular microscope and SEM, and stable isotope and trace element contents were obtained. Mineralogy of carbonate minerals were determined using <span class="hlt">crystal</span> shapes and qualitative Sr contents by EDAX together with trace element analysis. The carbonates are composed of high Mg-<span class="hlt">calcite</span>, low Mg-<span class="hlt">calcite</span> and aragonite. Aragonite <span class="hlt">crystals</span> show (1) radiating fibrous texture, (2) randomly oriented fibrous texture, (3) spherulitic fibrous texture, and (4) bladed texture, and <span class="hlt">calcite</span> <span class="hlt">crystals</span> show (1) foliated texture, (2) randomly bladed texture, (3) spherulitic fibrous texture, and (4) equant texture. Various <span class="hlt">crystal</span> shapes of aragonite and <span class="hlt">calcite</span> together with clear growth shapes of the <span class="hlt">crystals</span> suggest that they are inorganic in origin. Highly enriched carbon isotope compositions (δ13C = 0 ~ +5‰ vs. PDB) strongly indicate that they formed in methanogenic zone below sediment/water interface by the reaction between anoxic pore fluids and host sediments induced by methanogenic bacteria. However, a wide range of oxygen isotope values (δ18O = -5 ~ +5‰ vs. PDB) may indicate that porewater has been changed due to reaction between residual seawater and volcanic sediments. Four types of stable</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMPP31E..03B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMPP31E..03B"><span>Reconstructing Cambro-Ordovician Seawater Composition using Clumped Isotope Paleothermometry on <span class="hlt">Calcitic</span> and Phosphatic Brachiopods</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bergmann, K.; Robles, M.; Finnegan, S.; Hughes, N. C.; Eiler, J. M.; Fischer, W. W.</p> <p>2012-12-01</p> <p>A secular increase in δ18O values of marine fossils through early Phanerozoic time raises questions about the evolution of climate and the water cycle. This pattern suggests two end-member hypotheses 1) surface temperatures during early Paleozoic time were very warm, in excess of 40°C (tropical MAT), or 2) the isotopic composition of seawater increased by up to 7-8‰. It has been difficult to evaluate these hypotheses because the δ18O composition of fossils depends on both temperature and the δ18O of water. Furthermore, primary isotopic signatures can be overprinted by diagenetic processes that modify geological materials. This too could explain the decrease in δ18O values of marine fossils with age. Carbonate clumped isotope thermometry can constrain this problem by providing an independent measure of <span class="hlt">crystallization</span> temperature and, when paired with classical δ18O paleothermometry, can determine the isotopic composition of the fluid the mineral last equilibrated with. Combined with traditional tools, this method has the potential to untangle primary isotopic signatures from diagenetic signals. We measured the isotopic ordering of CO3 groups (Δ47) substituted into the phosphate lattice of phosphatic brachiopods in Cambrian strata. Phosphatic fossils are generally less soluble than carbonates in surface and diagenetic environments, and so are hypothesized to provide a more robust record of primary growth conditions. They also provide an archive prior to the rise of thick shelled <span class="hlt">calcitic</span> fossils during the Ordovician Radiation. Additionally, measurements of the δ18O of the CO3 groups can be compared with the δ18O of PO4 groups to test whether their mutual fractionation is consistent with primary growth and the apparent temperature recorded by carbonate clumped isotope measurements. We are constructing a phosphatic brachiopod calibration for carbonate clumped isotope thermometry, and Δ47 values of CO2 extracted from modern phosphatic brachiopods suggest</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.6047B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.6047B"><span>Aragonite / <span class="hlt">Calcite</span> seas and the evolution of biomineralization</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Balthasar, Uwe</p> <p>2015-04-01</p> <p>The vast majority of marine invertebrate skeletons are composed of the CaCO3 polymorphs aragonite and <span class="hlt">calcite</span>, yet the influence of seawater composition on the evolution of calcareous skeletal composition is poorly understood. The main theoretical framework in which the evolution of CaCO3 shell mineralogy is assessed is the aragonite-<span class="hlt">calcite</span> sea hypothesis with conventional thinking suggesting that a threshold in the marine Mg:Ca ratio determines CaCO3 polymorph formation. I present data from CaCO3 precipitation experiments to show that the concept of a distinct threshold is misleading because Mg:Ca ratio and temperature combined result in a Phanerozoic continuum of co-existing aragonite-<span class="hlt">calcite</span> seas with aragonite-facilitating conditions existing throughout the Phanerozoic in shallow warm-water (>20° C) environments. The stable reservoir of aragonite-favouring conditions in shallow warm water environments potentially explains the trend of increasing occurrences of skeletal aragonite throughout the Phanerozoic, particularly in the context of the 'out of the tropics' hypothesis. By contrast, the most prominent fluctuations with respect to aragonite-<span class="hlt">calcite</span> sea conditions can be expected to have occurred in mid- to high latitudes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20050000477&hterms=Amphibians&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DAmphibians','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20050000477&hterms=Amphibians&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DAmphibians"><span>Utricular otoconia of some amphibians have <span class="hlt">calcitic</span> morphology</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Pote, K. G.; Ross, M. D.</p> <p>1993-01-01</p> <p>This report concerns the morphological features of otoconia removed from the inner ear of four amphibian species. Results from scanning electron microscopic examination are compared based on the site of origin. These results show that utricular otoconia have a mineral structure that mimics <span class="hlt">calcite</span>, rather than the widely accepted idea that they are mineralized by calcium carbonate of the aragonite polymorph.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009GeCoA..73.6218R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009GeCoA..73.6218R"><span>Kinetics of gypsum nucleation and <span class="hlt">crystal</span> growth from Dead Sea brine</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Reznik, Itay J.; Gavrieli, Ittai; Ganor, Jiwchar</p> <p>2009-10-01</p> <p>The Dead Sea brine is supersaturated with respect to gypsum ( Ω = 1.42). Laboratory experiments and evaluation of historical data show that gypsum nucleation and <span class="hlt">crystal</span> growth kinetics from Dead Sea brine are both slower in comparison with solutions at a similar degree of supersaturation. The slow kinetics of gypsum precipitation in the Dead Sea brine is mainly attributed to the low solubility of gypsum which is due to the high Ca 2+/SO 42- molar ratio (115), high salinity (˜280 g/kg) and to Na + inhibition. Experiments with various clay minerals (montmorillonite, kaolinite) indicate that these minerals do not serve as <span class="hlt">crystallization</span> <span class="hlt">seeds</span>. In contrast, <span class="hlt">calcite</span> and aragonite which contain traces of gypsum impurities do prompt precipitation of gypsum but at a considerable slower rate than with pure gypsum. This implies that transportation inflow of clay minerals, <span class="hlt">calcite</span> and local <span class="hlt">crystallization</span> of minerals in the Dead Sea does not prompt significant heterogeneous precipitation of gypsum. Based on historical analyses of the Dead Sea, it is shown that over the last decades, as inflows to the lake decreased and its salinity increased, gypsum continuously precipitated from the brine. The increasing salinity and Ca 2+/SO 42- ratio, which results from the precipitation of gypsum, lead to even slower kinetics of nucleation and <span class="hlt">crystal</span> growth, which resulted in an increasing degree of supersaturation with respect to gypsum. Therefore, we predict that as the salinity of the Dead Sea brine continues to increase (accompanied by Dead Sea water level decline), although gypsum will continuously precipitate, the degree of supersaturation will increase furthermore due to progressively slower kinetics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20449036','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20449036"><span>Proton/calcium ion exchange behavior of <span class="hlt">calcite</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Villegas-Jiménez, Adrián; Mucci, Alfonso; Paquette, Jeanne</p> <p>2009-10-21</p> <p>The characterization of the proton sorptive properties of <span class="hlt">calcite</span> in aqueous solutions at 25 +/- 1 degrees C over a relatively wide range of chemical conditions (7.16 <or= pH <or= 9.7; 3 x 10(-5) M <or=SigmaCa <or= 5 x 10(-3) M; 10(-4) M <or=SigmaCO(2)<or= 1.7 x 10(-3) M) and solid : solution ratios (0.4 to 12.3 g L(-1)) was performed using a novel surface titration technique. A large net proton uptake, coupled with a significant release of Ca(2+) ions is consistently observed, greatly exceeding the theoretical number of reactive surface sites. These observations are interpreted as a fast proton/calcium exchange equilibrium between the solution and "exchangeable cation sites" (e.g., lattice positions) at and/or beneath the <span class="hlt">calcite</span> surface (species identified by "(exc)"), , that leads to a transient, "apparent" incongruent dissolution regime and the formation of a stable calcium-deficient, proton-enriched layer within the <span class="hlt">calcite</span> lattice under circum-neutral and alkaline regimes at standard conditions. The 2H(+)/Ca(2+) ion exchange is quantitatively described by the Langmuir-power exchange function under the Vanselow convention: where n = 1 and log(10)K(ex) = 13.0 +/- 0.3. This <span class="hlt">calcite</span> behavior, never reported before, masks surface equilibria and directly impacts the aqueous speciation of carbonate-rock systems with poor CO(2)(g) ventilation (e.g., aquifers, pore and deep sea waters, industrial reactors) via the buffering of pH and <span class="hlt">calcite</span> dissolution. In contrast, at fixed pCO(2) conditions, aqueous speciation remains unaffected upon CO(2)(g) sequestration resulting from ion exchange-induced <span class="hlt">calcite</span> precipitation: ([triple bond]CaCO3)2(exc) + CO2(g) + H2O <==> [triple bond]Ca(HCO3)2(exc) + CaCO3(s). Accordingly, reliable predictions of aqueous speciation in natural or engineered <span class="hlt">calcite</span>-containing systems at variable pCO(2) conditions must consider this exchange reaction and the associated K(ex). The postulated proton/calcium exchange may have far</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001GeCoA..65.4131H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001GeCoA..65.4131H"><span>The behavior of Ni 2+ on <span class="hlt">calcite</span> surfaces</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hoffmann, U.; Stipp, S. L. S.</p> <p>2001-11-01</p> <p>Transport of Ni 2+ in the geosphere plays a role in the formation of ore deposits as well as in the dispersion of contaminants in the environment. Some elements (Cd 2+, Zn 2+, Na +, K +, and Cl -) are known to diffuse in <span class="hlt">calcite</span> at the rate of nanometers in months, so questions arose about the ability of Ni 2+ to move away from adsorption sites at the surface into the bulk. Nickel incorporation into <span class="hlt">calcite</span> is limited by its high dehydration enthalpy and by its ligand field hindrance to entering the distorted octahedra of <span class="hlt">calcite</span>, but evidence exists that <span class="hlt">calcite</span> can tolerate several percent Ni 2+ in the structure. Cleaved samples of Iceland spar were exposed for 1 minute to solutions of 10 -3 M and 10 -2 M Ni(ClO 4) 2, the solution was physically removed and the samples were examined using the surface sensitive techniques: X-ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS) and Atomic Force Microscopy (AFM). XPS and TOF-SIMS showed that Ni 2+ was adsorbed while AFM confirmed that dissolution was taking place. The sample was stored in air and relative surface concentration and physical morphology were monitored for 2 years. Trends in the chemical data suggested statistically significant loss of surface Ni 2+ with time, but the decrease was very close to the limits for significance. AFM images demonstrated that surface topography of the Ni-exposed samples is modified by spontaneous recrystalization in the water layer adsorbed from air in exactly the same way that clean <span class="hlt">calcite</span> surfaces typically rearrange. This process could bury a small amount of Ni 2+ in the bulk, explaining the very weak loss. Limited burial of Ni 2+ within the near-surface could renew <span class="hlt">calcite</span> adsorption sites, thus increasing uptake capacity. Evidence indicates that surface recrystalization occurs even in very dry environments (<5% humidity). This means that burial could play a role in Ni 2+ mobility in unsaturated groundwater regimes or in fractures</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16678843','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16678843"><span>The inhibition of calcium carbonate <span class="hlt">crystal</span> growth by the cysteine-rich Mdm2 peptide.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Dalas, E; Chalias, A; Gatos, D; Barlos, K</p> <p>2006-08-15</p> <p>The <span class="hlt">crystal</span> growth of <span class="hlt">calcite</span>, the most stable calcium carbonate polymorph, in the presence of the cysteine-rich Mdm2 peptide (containing 48 amino acids in the ring finger configuration), has been investigated by the constant composition technique. <span class="hlt">Crystallization</span> took place exclusively on well-characterized <span class="hlt">calcite</span> <span class="hlt">crystals</span> in solutions supersaturated only with respect to this calcium carbonate salt. The kinetic results indicated a surface diffusion spiral growth mechanism. The presence of the Mdm2 peptide inhibited the <span class="hlt">crystal</span> growth of <span class="hlt">calcite</span> by 22-58% in the concentration range tested, through adsorption onto the active growth sites of the <span class="hlt">calcite</span> <span class="hlt">crystal</span> surface. The kinetic results favored a Langmuir-type adsorption model, and the value of the calculated affinity constant was k(aff)=147x10(4) dm(3)mol(-1), a(ads)=0.29.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeCoA.144..126L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeCoA.144..126L"><span>Aragonite, breunnerite, <span class="hlt">calcite</span> and dolomite in the CM carbonaceous chondrites: High fidelity recorders of progressive parent body aqueous alteration</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Martin R.; Lindgren, Paula; Sofe, Mahmood R.</p> <p>2014-11-01</p> <p>Carbonate minerals in CM carbonaceous chondrite meteorites, along with the silicates and sulphides with which they are intergrown, provide a detailed record of the nature and evolution of parent body porosity and permeability, and the chemical composition, temperature and longevity of aqueous solutions. Fourteen meteorites were studied that range in petrologic subtype from mildly aqueously altered CM2.5 to completely hydrated CM2.0. All of them contain <span class="hlt">calcite</span>, whereas aragonite occurs only in the CM2.5-CM2.2 meteorites and dolomite in the CM2.2-CM2.0. All of the aragonite <span class="hlt">crystals</span>, and most of the <span class="hlt">calcite</span> and dolomite grains, formed during early stages of parent body aqueous alteration by cementation of pores produced by the melting of tens of micrometre size particles of H2O-rich ice. Aragonite was the first carbonate to precipitate in the CM2.5 to CM2.2 meteorites, and grew from magnesium-rich solutions. In the least altered of these meteorites the aragonite <span class="hlt">crystals</span> formed in clusters owing to physical restriction of aqueous fluids within the low permeability matrix. The strong correlation between the petrologic subtype of a meteorite, the abundance of its aragonite <span class="hlt">crystals</span> and the proportion of them that have preserved <span class="hlt">crystal</span> faces, is because aragonite was dissolved in the more altered meteorites on account of their higher permeability, and/or greater longevity of the aqueous solutions. Dolomite and breunnerite formed instead of aragonite in some of the CM2.1 and CM2.2 meteorites owing to higher parent body temperatures. The pore spaces that remained after precipitation of aragonite, dolomite and breunnerite cements were occluded by <span class="hlt">calcite</span>. Following completion of cementation, the carbonates were partially replaced by phyllosilicates and sulphides. <span class="hlt">Calcite</span> in the CM2.5-CM2.2 meteorites was replaced by Fe-rich serpentine and tochilinite, followed by Mg-rich serpentine. In the CM2.1 and CM2.0 meteorites dolomite, breunnerite and <span class="hlt">calcite</span> were replaced by Fe</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeCoA.156...75R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeCoA.156...75R"><span>Experimental study of the replacement of <span class="hlt">calcite</span> by calcium sulphates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ruiz-Agudo, E.; Putnis, C. V.; Hövelmann, J.; Álvarez-Lloret, P.; Ibáñez-Velasco, A.; Putnis, A.</p> <p>2015-05-01</p> <p>Among the most relevant mineral replacement reactions are those involving sulphates and carbonates, which have important geological and technological implications. Here it is shown experimentally that during the interaction of <span class="hlt">calcite</span> (CaCO3) cleavage surfaces with sulphate-bearing acidic solutions, <span class="hlt">calcite</span> is ultimately replaced by gypsum (CaSO4 2H2O) and anhydrite (CaSO4), depending on the reaction temperature. Observations suggest that this occurs most likely via an interface-coupled dissolution-precipitation reaction, in which the substrate is replaced pseudomorphically by the product. At 120 and 200 °C gypsum and/or bassanite (CaSO4·0.5H2O) form as precursor phases for the thermodynamically stable anhydrite. Salinity promotes the formation of less hydrated precursor phases during the replacement of <span class="hlt">calcite</span> by anhydrite. The reaction stops before equilibrium with respect to <span class="hlt">calcite</span> is reached and during the course of the reaction most of the bulk solutions are undersaturated with respect to the precipitating phase(s). A mechanism consisting of the dissolution of small amounts of solid in a thin layer of fluid at the mineral-fluid interface and the subsequent precipitation of the product phase from this layer is in agreement with these observations. PHREEQC simulations performed in the framework of this mechanism highlight the relevance of transport and surface reaction kinetics on the volume change associated with the CaCO3-CaSO4 replacement. Under our experimental conditions, this reaction occurs with a positive volume change, which ultimately results in passivation of the unreacted substrate before <span class="hlt">calcite</span> attains equilibrium with respect to the bulk solution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1339818','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1339818"><span>Nanometer-Scale Chemistry of a <span class="hlt">Calcite</span> Biomineralization Template: Implications for Skeletal Composition and Nucleation</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Branson, Oscar; Bonnin, Elisa A.; Perea, Daniel E.; Spero, Howard J.; Zhu, Zihua; Winters, Maria; Hönisch, Bärbel; Russell, Ann D.; Fehrenbacher, Jennifer S.; Gagnon, Alexander C.</p> <p>2016-10-28</p> <p>Biomineralizing organisms exhibit exquisite control over skeletal morphology and composition. The promise of understanding and harnessing this feat of natural engineering has motivated an intense search for the mechanisms that direct in vivo mineral self-assembly. We used atom probe tomography, a sub-nanometer 3D chemical mapping technique, to examine the chemistry of a buried organic-mineral interface in biomineral <span class="hlt">calcite</span> from a marine foraminifer. The chemical patterns at this interface capture the processes of early biomineralization, when the shape, mineralogy, and orientation of skeletal growth are initially established. Sodium is enriched by a factor of nine on the organic side of the interface. Based on this pattern, we suggest that sodium plays an integral role in early biomineralization, potentially altering interfacial energy to promote <span class="hlt">crystal</span> nucleation, and that interactions between organic surfaces and electrolytes other than calcium or carbonate could be a crucial aspect of CaCO3 biomineralization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA254905','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA254905"><span>Surface Analysis of Ln(2-x)Ce(x)CuO4 (Ln = Pr and Nd) Single <span class="hlt">Crystals</span> Grown by the Top <span class="hlt">Seeded</span> Solution Method</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1992-05-01</p> <p>crystalline structure was probed by ion beam channeling. The orientation and lattice parameters of the <span class="hlt">crystals</span> were determined by X-ray diffraction and the superconductivity of the specimens was monitored using a SQUID magnetometer. The results indicate that the <span class="hlt">crystals</span> grown by the TSSG</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AtmEn..42.5672H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AtmEn..42.5672H"><span>Water adsorption and cloud condensation nuclei activity of <span class="hlt">calcite</span> and <span class="hlt">calcite</span> coated with model humic and fulvic acids</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hatch, Courtney D.; Gierlus, Kelly M.; Schuttlefield, Jennifer D.; Grassian, Vicki H.</p> <p></p> <p>Recent studies have shown that organics can alter the water adsorption and cloud condensation nuclei (CCN) activity of common deliquescent species in the Earth's atmosphere. However, very little is known about the effect of organics on water adsorption and CCN activity of insoluble nuclei, such as mineral dust aerosol. A large fraction of unidentified organic material in aerosol particles is composed of poly-acidic compounds resembling humic substances. The presence of these humic-like substances (HULIS) can alter the water adsorption and CCN activity of mineral dust aerosol. We have measured the CCN activity of model humic and fulvic acids and of mineral dust particles coated with these substances in the laboratory. We find that coatings of humic and fulvic acids on <span class="hlt">calcite</span> particles significantly increases water adsorption compared to uncoated particles. CCN measurements indicate that humic- or fulvic acid-coated <span class="hlt">calcite</span> particles are more CCN active than uncoated <span class="hlt">calcite</span> particles. Additionally, thicker coatings of humic or fulvic acids appear to result in more efficient CCN activity. Thus, mineral dust particles coated with high molecular weight organic materials will take up more water and become more efficient CCN in the atmosphere than uncoated mineral dust particles, potentially altering the effect of mineral dust on the Earth's climate. In addition to the experimental results, we have explored a newly modified Köhler theory for predicting the CCN activity of insoluble, wettable particles based on multi layer water adsorption measurements of <span class="hlt">calcite</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100035124','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100035124"><span>Stability of Basalt plus Anhydrite plus <span class="hlt">Calcite</span> at HP-HT: Implications for Venus, the Earth and Mars</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Martin, A. M.; Righter, K.; Treiman, A. H.</p> <p>2010-01-01</p> <p>"Canali" observed at Venus surface by Magellan are evidence for very long melt flows, but their composition and origin remain uncertain. The hypothesis of water-rich flow is not reasonable regarding the temperature at Venus surface. The length of these channels could not be explained by a silicate melt composition but more likely, by a carbonate-sulfate melt which has a much lower viscosity (Kargel et al 1994). One hypothesis is that <span class="hlt">calcite</span> CaCO3 and anhydrite CaSO4 which are alteration products of basalts melted during meteorite impacts. A famous example recorded on the Earth (Chicxulub) produced melt and gas rich in carbon and sulfur. <span class="hlt">Calcite</span> and sulfate evaporites are also present on Mars surface, associated with basalts. An impact on these materials might release C- and S-rich melt or fluid. Another type of planetary phenomenon (affecting only the Earth) might provoke a high pressure destabilization of basalt+anhydrite+<span class="hlt">calcite</span>. Very high contents of C and S are measured in some Earth s magmas, either dissolved or in the form of <span class="hlt">crystals</span> (Luhr 2008). As shown by the high H content and high fO2 of primary igneous anhydrite-bearing lavas, the high S content in their source may be explained by subduction of an anhydrite-bearing oceanic crust, either directly (by melting followed by eruption) or indirectly (by release of S-rich melt or fluid that metasomatize the mantle) . <span class="hlt">Calcite</span> is a major product of oceanic sedimentation and alteration of the crust. Therefore, sulfate- and <span class="hlt">calcite</span>-rich material may be subducted to high pressures and high temperatures (HP-HT) and release S- and C-rich melts or fluids which could influence the composition of subduction zone lavas or gases. Both phenomena - meteorite impact and subduction - imply HP-HT conditions - although the P-T-time paths are different. Some HP experimental/theoretical studies have been performed on basalt/eclogite, <span class="hlt">calcite</span> and anhydrite separately or on a combination of two. In this study we performed piston</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.P53B1520M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.P53B1520M"><span>Stability of basalt+anhydrite+<span class="hlt">calcite</span> at HP-HT: implications for Venus, the Earth and Mars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Martin, A. M.; Righter, K.; Treiman, A. H.</p> <p>2010-12-01</p> <p>“Canali” observed at Venus’ surface by Magellan are evidence for very long melt flows, but their composition and origin remain uncertain. The hypothesis of water-rich flow is not reasonable regarding Venus’ surface temperature. The length of these channels could not be explained by a silicate melt composition but more likely, by a carbonate-sulfate melt which has a much lower viscosity (Kargel et al 1994). One hypothesis is that <span class="hlt">calcite</span> CaCO3 and anhydrite CaSO4 - which are alteration products of basalts - melted during meteorite impacts. A famous example recorded on the Earth (Chicxulub) produced melt and gas rich in carbon and sulfur. <span class="hlt">Calcite</span> and sulfate evaporites are also present on Mars surface, associated with basalts. An impact on these materials may release C- and S-rich melt or fluid. Another type of planetary phenomenon (affecting only the Earth) might provoke a high pressure destabilization of basalt+anhydrite+<span class="hlt">calcite</span>. Very high contents of C and S are measured in some Earth’s magmas, either dissolved or in the form of <span class="hlt">crystals</span> (Luhr 2008). As shown by the high H content and high fO2 of primary igneous anhydrite-bearing lavas, the high S content in their source may be explained by the subduction of an anhydrite-bearing oceanic crust, either directly (by melting followed by eruption) or indirectly (by release of S-rich melt or fluid that metasomatize the mantle). <span class="hlt">Calcite</span> is a major product of oceanic sedimentation and alteration of the crust. Therefore, sulfate- and <span class="hlt">calcite</span>-rich material may be subducted to high pressures and high temperatures (HP-HT) and release S- and C-rich melts or fluids which could influence the composition of subduction zone lavas or gases. Both phenomena - meteorite impact and subduction - imply HP-HT conditions - although the P-T-time paths are different. Some HP experimental/theoretical studies have been performed on basalt/eclogite, <span class="hlt">calcite</span> and anhydrite separately or on a combination of two. In this study we</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5025825','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5025825"><span>Occlusion of Sulfate-Based Diblock Copolymer Nanoparticles within <span class="hlt">Calcite</span>: Effect of Varying the Surface Density of Anionic Stabilizer Chains</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p></p> <p>2016-01-01</p> <p>Polymerization-induced self-assembly (PISA) offers a highly versatile and efficient route to a wide range of organic nanoparticles. In this article, we demonstrate for the first time that poly(ammonium 2-sulfatoethyl methacrylate)-poly(benzyl methacrylate) [PSEM–PBzMA] diblock copolymer nanoparticles can be prepared with either a high or low PSEM stabilizer surface density using either RAFT dispersion polymerization in a 2:1 v/v ethanol/water mixture or RAFT aqueous emulsion polymerization, respectively. We then use these model nanoparticles to gain new insight into a key topic in materials chemistry: the occlusion of organic additives into inorganic <span class="hlt">crystals</span>. Substantial differences are observed for the extent of occlusion of these two types of anionic nanoparticles into <span class="hlt">calcite</span> (CaCO3), which serves as a suitable model host <span class="hlt">crystal</span>. A low PSEM stabilizer surface density leads to uniform nanoparticle occlusion within <span class="hlt">calcite</span> at up to 7.5% w/w (16% v/v), while minimal occlusion occurs when using nanoparticles with a high PSEM stabilizer surface density. This counter-intuitive observation suggests that an optimum anionic surface density is required for efficient occlusion, which provides a hitherto unexpected design rule for the incorporation of nanoparticles within <span class="hlt">crystals</span>. PMID:27509298</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JEMat..45.4460D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JEMat..45.4460D"><span>Top <span class="hlt">Seeded</span> Solution Growth, Structural and Vibrational Analyses of K1- x Na x Gd(WO4)2 (0.0 ≤ x ≤ 0.2) Single <span class="hlt">Crystals</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Durairajan, A.; Thangaraju, D.; Valente, M. A.; Moorthy Babu, S.</p> <p>2016-08-01</p> <p>Laser host single <span class="hlt">crystals</span> of K1- x Na x Gd(WO4)2 (0.0 ≤ x ≤ 0.2) have been grown by high temperature top <span class="hlt">seeded</span> solution with low viscus K2WO4 as flux. The powder x-ray diffraction pattern of the synthesised charge confirmed the crystalline quality and possible incorporation of sodium in the KGd(WO4)2 (KGW) matrix. Estimated lattice parameters of the grown <span class="hlt">crystals</span> revealed that there were no anomalous structural changes due to the incorporation of sodium in the KGW matrix. The change in structural phase transition and its thermal stability due to addition of sodium ions have been studied through differential thermal analysis. The homogeneous distribution of sodium and other metal ions in the matrix were qualitatively studied from energy-dispersive x-ray spectroscopy measurements. The Raman and Fourier transform infrared spectroscopy analyses have shown the influence of vibrational changes due to the incorporation of sodium ions in KGW. The optical absorption studies have shown the broad absorption band in the near-ultra violet region corresponding to the W6+ to O2- charge transfer band. These results suggest that incorporation of sodium in a KGW matrix appear to have modulated the physical properties of the grown <span class="hlt">crystals</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22360549','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22360549"><span><span class="hlt">Crystallization</span> and preliminary X-ray analysis of ginkbilobin-2 from Ginkgo biloba <span class="hlt">seeds</span>: a novel antifungal protein with homology to the extracellular domain of plant cysteine-rich receptor-like kinases</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Miyakawa, Takuya; Sawano, Yoriko; Miyazono, Ken-ichi; Hatano, Ken-ichi; Tanokura, Masaru</p> <p>2007-09-01</p> <p>Purification and <span class="hlt">crystallization</span> of ginkbilobin-2 and its selenomethionine derivative allowed the collection of complete data to 2.38 Å resolution and multiwavelength anomalous diffraction data sets, respectively. The antifungal protein ginkbilobin-2 (Gnk2) from Ginkgo biloba <span class="hlt">seeds</span> does not show homology to other pathogenesis-related proteins, but does show homology to the extracellular domain of plant cysteine-rich receptor-like kinases. Native Gnk2 purified from ginkgo nuts and the selenomethionine derivative of recombinant Gnk2 (SeMet-rGnk2) were <span class="hlt">crystallized</span> by the sitting-drop vapour-diffusion method using different precipitants. X-ray diffraction data were collected from Gnk2 at 2.38 Å resolution and from SeMet-rGnk2 at 2.79 Å resolution using a synchrotron-radiation source. The <span class="hlt">crystals</span> of both proteins belonged to the primitive cubic space group P2{sub 1}3, with unit-cell parameters a = b = c = 143.2 Å.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PApGe.171.2617V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PApGe.171.2617V"><span>Frictional Properties and Microstructure of <span class="hlt">Calcite</span>-Rich Fault Gouges Sheared at Sub-Seismic Sliding Velocities</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Verberne, B. A.; Spiers, C. J.; Niemeijer, A. R.; De Bresser, J. H. P.; De Winter, D. A. M.; Plümper, O.</p> <p>2014-10-01</p> <p>We report an experimental and microstructural study of the frictional properties of simulated fault gouges prepared from natural limestone (96 % CaCO3) and pure <span class="hlt">calcite</span>. Our experiments consisted of direct shear tests performed, under dry and wet conditions, at an effective normal stress of 50 MPa, at 18-150 °C and sliding velocities of 0.1-10 μm/s. Wet experiments used a pore water pressure of 10 MPa. Wet gouges typically showed a lower steady-state frictional strength ( μ = 0.6) than dry gouges ( μ = 0.7-0.8), particularly in the case of the pure <span class="hlt">calcite</span> samples. All runs showed a transition from stable velocity strengthening to (potentially) unstable velocity weakening slip above 80-100 °C. All recovered samples showed patchy, mirror-like surfaces marking boundary shear planes. Optical study of sections cut normal to the shear plane and parallel to the shear direction showed both boundary and inclined shear bands, characterized by extreme grain comminution and a crystallographic preferred orientation. Cross-sections of boundary shears, cut normal to the shear direction using focused ion beam—SEM, from pure <span class="hlt">calcite</span> gouges sheared at 18 and 150 °C, revealed dense arrays of rounded, ~0.3 μm-sized particles in the shear band core. Transmission electron microscopy showed that these particles consist of 5-20 nm sized <span class="hlt">calcite</span> nanocrystals. All samples showed evidence for cataclasis and <span class="hlt">crystal</span> plasticity. Comparing our results with previous models for gouge friction, we suggest that frictional behaviour was controlled by competition between <span class="hlt">crystal</span> plastic and granular flow processes active in the shear bands, with water facilitating pressure solution, subcritical cracking and intergranular lubrication. Our data have important implications for the depth of the seismogenic zone in tectonically active limestone terrains. Contrary to recent claims, our data also demonstrate that nanocrystalline mirror-like slip surfaces in <span class="hlt">calcite</span>(-rich) faults are not</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3280721','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3280721"><span>Sr2+/Ca2+ and 44Ca/40Ca fractionation during inorganic <span class="hlt">calcite</span> formation: III. Impact of salinity/ionic strength</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Tang, Jianwu; Niedermayr, Andrea; Köhler, Stephan J.; Böhm, Florian; Kısakürek, Basak; Eisenhauer, Anton; Dietzel, Martin</p> <p>2012-01-01</p> <p>In order to apply Sr/Ca and 44Ca/40Ca fractionation during calcium carbonate (CaCO3) formation as a proxy to reconstruct paleo-environments, it is essential to evaluate the impact of various environmental factors. In this study, a CO2 diffusion technique was used to <span class="hlt">crystallize</span> inorganic <span class="hlt">calcite</span> from aqueous solutions at different ionic strength/salinity by the addition of NaCl at 25 °C. Results show that the discrimination of Sr2+ versus Ca2+ during <span class="hlt">calcite</span> formation is mainly controlled by precipitation rate (R in μmol/m2/h) and is weakly influenced by ionic strength/salinity. In analogy to Sr incorporation, 44Ca/40Ca fractionation during precipitation of <span class="hlt">calcite</span> is weakly influenced by ionic strength/salinity too. At 25 °C the calcium isotope fractionation between <span class="hlt">calcite</span> and aqueous calcium ions (Δ44/40Cacalcite-aq = δ44/40Cacalcite − δ44/40Caaq) correlates inversely to log R values for all experiments. In addition, an inverse relationship between Δ44/40Cacalcite-aq and log DSr, which is independent of temperature, precipitation rate, and aqueous (Sr/Ca)aq ratio, is not affected by ionic strength/salinity either. Considering the log DSr and Δ44/40Cacalcite-aq relationship, Sr/Ca and δ44/40Cacalcite values of precipitated <span class="hlt">calcite</span> can be used as an excellent multi-proxy approach to reconstruct environmental conditions (e.g., temperature, precipitation rate) of <span class="hlt">calcite</span> growth and diagenetic alteration. PMID:22347722</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998GeCoA..62..433S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998GeCoA..62..433S"><span>Cosmogenic Chlorine-36 Production in <span class="hlt">Calcite</span> by Muons</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stone, J. O. H.; Evans, J. M.; Fifield, L. K.; Allan, G. L.; Cresswell, R. G.</p> <p>1998-02-01</p> <p>At depths below a few metres, 36Cl production in <span class="hlt">calcite</span> is initiated almost entirely by cosmic ray muons. The principal reactions are (1) direct negative muon capture by Ca; 40Ca(μ -,α) 36Cl, and (2) capture by 35Cl of secondary neutrons produced in muon capture and muon-induced photodisintegration reactions. We have determined rates for 36Cl and neutron production due to muon capture in <span class="hlt">calcite</span> from a 20 m (5360 g cm -2) depth profile in limestone. The 36Cl yield from muon capture by Ca in pure <span class="hlt">calcite</span> is 0.012 ± 0.002 atom per stopped negative muon. The surface production rate of 36Cl by muon capture on Ca in <span class="hlt">calcite</span> is, therefore, 2.1 ± 0.4 atom g -1a -1 at sea level and high latitude, approximately 11% of the production rate by Ca spallation. If it is assumed that 34% of the negative muons are captured by the Ca atom in <span class="hlt">calcite</span>, the α-yield from 40Ca following muon capture is 0.043 ± 0.008, somewhat lower than the result of a recent muon irradiation experiment (0.062 ± 0.020), but well within the extremes of existing theoretical predictions (0.0033-0.15). The average neutron yield following muon capture in pure <span class="hlt">calcite</span> is 0.44 ± 0.15 secondary neutrons per stopped negative muon, in good agreement with existing theoretical predictions. Cosmogenic isotope production by muons must be taken into account when dating young geomorphic surfaces, especially those created by excavation of only a few metres of overlying rock. Attention to isotope production by muons is also crucial to determining surface erosion rates accurately. Due to the deep penetration of muons compared to cosmic ray hadrons, the accumulation of muon-produced 36Cl is less sensitive to erosion than that of spallogenic 36Cl. Although production by muons at the surface is only a small fraction of production by spallation, the fraction of muon-produced 36Cl in rapidly eroding limestone surfaces can approach 50%. In such cases, erosion rates estimated using conventional models which attribute</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1812908G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1812908G"><span>Growth rate controlled barium partitioning in <span class="hlt">calcite</span> and aragonite</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Goetschl, Katja Elisabeth; Mavromatis, Vasileios; Baldermann, Andre; Purgstaller, Bettina; Dietzel, Martin</p> <p>2016-04-01</p> <p>The barium (Ba) content and the Ba/Ca molar ratios in biogenic and abiotic carbonates have been widely used from the scientific community as a geochemical proxy especially in marine and early diagenetic settings. The Ba content of carbonate minerals has been earlier associated to changes in oceanic circulation that may have been caused by upwelling, changes in weathering regimes and river-runoff as well as melt water discharge. The physicochemical controls of Ba ion incorporation in the two most abundant CaCO3 polymorphs found in Earth's surface environments, i.e. <span class="hlt">calcite</span> and aragonite, have adequately been studied only for <span class="hlt">calcite</span>. These earlier studies (i.e. [1]) suggest that at increasing growth rate, Ba partitioning in <span class="hlt">calcite</span> is increasing as well. In contrast, to date the effect of growth rate on the partitioning of Ba in aragonite remains questionable, despite the fact that this mineral phase is the predominant carbonate-forming polymorph in shallow marine environments. To shed light on the mechanisms controlling Ba ion uptake in carbonates in this study we performed steady-state Ba co-precipitation experiments with <span class="hlt">calcite</span> and aragonite at 25°C. The obtained results for the partitioning of Ba in <span class="hlt">calcite</span> are in good agreement with those reported earlier by [1], whereas those for aragonite indicate a reduction of Ba partitioning at elevated aragonite growth rates, with the partitioning coefficient value between solid and fluid to be approaching the unity. This finding is good agreement with the formation of a solid solution in the aragonite-witherite system, owing to the isostructural crystallography of the two mineral phases. Moreover, our data set provides new insights that are required for reconstructing the evolution of the Ba content of pristine marine versus diagenetically altered carbonate minerals commonly occurring in marine subfloor settings, as the thermodynamically less stable aragonite will transform to <span class="hlt">calcite</span> enriched in Ba, whilst affecting</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004JCrGr.263..536K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004JCrGr.263..536K"><span>A novel insulin microcrystals preparation using a <span class="hlt">seed</span> zone method</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kwon, Jai-Hyun; Kim, Chan-Wha</p> <p>2004-03-01</p> <p>Milling and supercritical fluid technology have been used to prepare particles suitable for pulmonary delivery, but problems remain, e.g., the loss of protein activity, the heterogeneity of drug particles including shape, size etc., process yield, and the applicability for industrial production process. Therefore, in order to develop a novel process for particle preparation, <span class="hlt">crystallization</span> was investigated using insulin as a model protein. The relation between the number of <span class="hlt">seed</span> particles and the final <span class="hlt">crystal</span> size was investigated, and a novel microcrystallization process, named “<span class="hlt">seed</span> zone” method, was developed. The size of <span class="hlt">crystals</span> was inversely proportional to the number of <span class="hlt">seeds</span> in <span class="hlt">crystallizing</span> solution. Spontaneous <span class="hlt">crystallization</span> occurred around pH 6 in acetic acid solution, however, more than 60% of <span class="hlt">crystals</span> were bigger than 5 μm with two peak size distributions. On the contrary, microcrystals with a mean diameter of 3 μm were prepared using a <span class="hlt">seed</span> zone method. The “<span class="hlt">seed</span> zone” is a pH range where the <span class="hlt">seed</span> particles are stable in <span class="hlt">crystallizing</span> solution. Almost 90% (in volume) of microcrystals were under 5 μm, and the yield of <span class="hlt">crystallization</span> was maintained at 90% or higher. In the <span class="hlt">seed</span> zone, nano-sized particles (96 nm) with narrow size distributions were identified. Therefore, it is likely that these nano-sized particles would be used as <span class="hlt">seeds</span> in microcrystals formation. It is suggested that insulin microcrystallization using a <span class="hlt">seed</span> zone could be a useful particle preparation process in pharmaceutical industry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeCoA.148..343S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeCoA.148..343S"><span>U(VI) behaviour in hyperalkaline <span class="hlt">calcite</span> systems</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smith, Kurt F.; Bryan, Nicholas D.; Swinburne, Adam N.; Bots, Pieter; Shaw, Samuel; Natrajan, Louise S.; Mosselmans, J. Frederick W.; Livens, Francis R.; Morris, Katherine</p> <p>2015-01-01</p> <p>The behaviour of U(VI) in hyperalkaline fluid/<span class="hlt">calcite</span> systems was studied over a range of U(VI) concentrations (5.27 × 10-5 μM to 42.0 μM) and in two high pH systems, young and old synthetic cement leachate in batch sorption experiments. These systems were selected to be representative of young- (pH 13.3) and old-stage (pH 10.5) leachate evolution within a cementitious geological disposal facility. Batch sorption experiments, modelling, extended X-ray absorption fine structure spectroscopy, electron microscopy, small angle X-ray scattering and luminescence spectroscopy were used to define the speciation of U(VI) across the systems of study. At the lowest concentrations (5.27 × 10-5 μM 232U(VI)) significant U removal was observed for both old and young cement leachates, and this was successfully modelled using a first order kinetic adsorption modelling approach. At higher concentrations (>4.20 μM) in the young cement leachate, U(VI) showed no interaction with the <span class="hlt">calcite</span> surface over an 18 month period. Small angle X-ray scattering techniques indicated that at high U concentrations (42.0 μM) and after 18 months, the U(VI) was present in a colloidal form which had little interaction with the <span class="hlt">calcite</span> surface and consisted of both primary and aggregated particles with a radius of 7.6 ± 1.1 and 217 ± 24 Å, respectively. In the old cement leachate, luminescence spectroscopy identified two surface binding sites for U(VI) on <span class="hlt">calcite</span>: in the system with 0.21 μM U(VI), a liebigite-like Ca2UO2(CO3)3 surface complex was identified; at higher U(VI) concentrations (0.42 μM), a second binding site of undetermined coordination was identified. At elevated U(VI) concentrations (>2.10 μM) in old cement leachate, both geochemical data and luminescence spectroscopy suggested that surface mediated precipitation was controlling U(VI) behaviour. A focused ion beam mill was used to create a section across the U(VI) precipitate-<span class="hlt">calcite</span> interface. Transmission electron</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002GBioC..16.1065S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002GBioC..16.1065S"><span>Planktic foraminiferal sedimentation and the marine <span class="hlt">calcite</span> budget</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schiebel, Ralf</p> <p>2002-12-01</p> <p>The vertical flux and sedimentation rate of planktic foraminiferal tests are quantified and a global planktic foraminiferal CaCO3 budget is presented. Test and <span class="hlt">calcite</span> flux rates are calculated according to the distribution of species obtained from multinet and sediment trap samples. Modern planktic foraminiferal population dynamics are discussed as a prerequisite for the quantification of the <span class="hlt">calcite</span> budget, highlighting the importance of ecological, autecological (e.g., reproduction), and biogeochemical conditions that determine the presence or absence of species. To complete the open-marine, particulate CaCO3 inventory, the contribution of coccolithophores, pteropods, and calcareous dinophytes is discussed. Based on the studied regions, the global planktic foraminiferal <span class="hlt">calcite</span> flux rate at 100 m depth amounts to 1.3-3.2 Gt yr-1, equivalent to 23-56% of the total open marine CaCO3 flux. The preservation of tests varies on a regional and temporal scale, and is affected by local hydrography and dissolution. During most of the year (off-peak periods), many tests dissolve above 700-m water depth while settling through the water column, with on average only 1-3% of the initially exported CaCO3 reaching the deep-seafloor. Pulsed flux events, mass dumps of fast settling particles, yield a major contribution of tests to the formation of deep-sea sediments. On average, ˜25% of the initially produced planktic foraminiferal test CaCO3 settles on the seafloor. The total planktic foraminiferal contribution of CaCO3 to global surface sediments amounts to 0.36-0.88 Gt yr-1, ˜32-80% of the total deep-marine <span class="hlt">calcite</span> budget.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5438497','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5438497"><span>Interaction of copper with the surface of <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Franklin, M.L.; Morse, J.W.</p> <p>1981-05-01</p> <p>The interaction of Cu ions in solution with the surface of <span class="hlt">calcite</span> has been studied in a range of solutions from pure water to seawater. Observations of the uptake of Cu from solution onto <span class="hlt">calcite</span> indicates that the process is rapid and strong in both distilled water and seawater. In distilled water, Cu uptake is directly proportional to the concentration of Cu in solution; Cu/sub s/ = K/sub s/Cu/sub 1/. This Cu/sub s/ dependence on Cu/sub 1/ is linear over the entire Cu concentration range studied (0.1 to 200 ..mu..M). Results do not indicate the formation of a precipitate of either malachite or copper carbonate. In seawater, the uptake of Cu is also directly proportional to the concentration of Cu/sub 1/ up to a limiting value of approximately 13 ..mu..M. The average value for K/sub s/ in seawater, 0.24 +- 0.06 (Cu/sub 1/ less than or equal to 13 ..mu..M), is approximately an order of magnitude less than in distilled water. This is probably the result of smaller Cu/sub 1/ activity coefficients and increased site competition by other ions in seawater. Attempts to increase the Cu/sub 1/ concentration above 13 ..mu..M resulted in the additional Cu being deposited on the surface of the <span class="hlt">calcite</span>. A possible explanation for this behavior is the formation of a precipitate of malachite on the <span class="hlt">calcite</span> surface. The value of K/sub s/ decreased slightly with increasing solid to solution ratios in seawater.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/15010163','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/15010163"><span>Variation in <span class="hlt">Calcite</span> Dissolution Rates: A Fundamental Problem?</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Arvidson, Rolf S.; Ertan, Inci E.; Amonette, James E.; Luttge, Andreas</p> <p>2003-05-01</p> <p>A comparison of published <span class="hlt">calcite</span> dissolution rates measured far from equilibrium at a pH of {approx} 6 and above shows well over an order of magnitude in variation. Recently published AFM step velocities extend this range further still. In an effort to understand the source of this variation, and to provide additional constraint from a new analytical approach, we have measured dissolution rates by vertical scanning interferometry. In areas of the <span class="hlt">calcite</span> cleavage surface dominated by etch pits, our measured dissolution rate is 10{sup 10.95} mol/cm{sup 2}/s (PCO{sub 2} 10{sup 3.41} atm, pH 8.82), 5 to {approx}100 times slower than rates published in bulk powder experiments, although similar to rates derived from AFM step velocities. On cleavage surfaces free of local etch pit development, dissolution is limited by a slow, ''global'' rate (10{sup 11.68} mol/cm{sup 2}/s). Although these differences confirm the importance of etch pit (defect) distribution as a controlling mechanism in <span class="hlt">calcite</span> dissolution, they also suggest that ''bulk'' <span class="hlt">calcite</span> dissolution rates observed in powder experiments may derive substantial enhancement from grain boundaries having high step and kink density. We also observed significant rate inhibition by introduction of dissolved manganese. At 2.0 {micro}M Mn, the rate diminished to 10{sup 12.4} mol/cm{sup 2}/s, and the well formed rhombic etch pits that characterized dissolution in pure solution were absent. These results are in good agreement with the pattern of manganese inhibition in published AFM step velocities, assuming a step density on smooth terraces of {approx} 9 {micro}m{sup -1}.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/826394','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/826394"><span>Microbially-Mediated Subsurface <span class="hlt">Calcite</span> Precipitation for Removal of Hazardous Divalent Cations</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Colwell, Frederick S.; Smith, R.W.; Ferris, F. Gratn; Ingram, Jani C.; Reysenbach, A.-L.; Fujita, Yoshiko; Tyler, T.L.; Taylor, J.L.; Banta, A.; Delwiche, M.E.; McLing, T.; Cortez, Marnie, M.; Watwood, M.E.</p> <p>2003-03-27</p> <p>We are investigating microbially-mediated acceleration of <span class="hlt">calcite</span> precipitation and co-precipitation of hazardous divalent cations (e.g., 90Sr) in <span class="hlt">calcite</span> saturated subsurface systems. In theory, the addition of urea to an aquifer or vadose zone and its subsequent hydrolysis by indigenous microbes will cause an increase in alkalinity, pH and <span class="hlt">calcite</span> precipitation. Lab studies indicated the ability of various bacteria to precipitate <span class="hlt">calcite</span> through urea hydrolysis and that incorporation of strontium in biogenically-formed <span class="hlt">calcite</span> is greater than in abiotically formed <span class="hlt">calcite</span>. Results from a field experiment in a pristine location in the Snake River Plain aquifer involving the phased addition of molasses and then urea showed increases in total cell numbers, rate of urea hydrolysis and <span class="hlt">calcite</span> formation during the study. The combined diagnostic approaches of microbiology, molecular ecology and analytical chemistry demonstrate the feasibility of this biogeochemical manipulation for subsurface remediation at arid Western DOE sites such as Hanford and INEEL.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5322967','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5322967"><span><span class="hlt">Calcite</span> deposition at Miravalles geothermal field, Costa Rica</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Vaca, L.; Alvarado, A.; Corrales, R. )</p> <p>1989-01-01</p> <p>The <span class="hlt">calcite</span> deposition problem at Miravalles has been studied since it was observed in the first three wells drilled on the slopes of the Miravalles Volcano. Long-term tests have been carried out to study reservoir characteristics. The change in the production behavior of the wells with the restriction imposed by the deposited <span class="hlt">calcite</span> has been studied trying to evaluate and quantify the scaling problem. Work is being done on predictions of the deposition rate, location and distribution of the deposited mineral inside the wells. This work was compared with real data obtained from caliper logs of the wells before and after production. The feasibility of the first 55 MW power plant has been demonstrated. It was considered that the solution for the <span class="hlt">calcite</span> problem is the reaming during discharge of the wells trying at the same time to minimize the cleaning interventions with a new well design. It is believed, due to the thermodynamics and chemical characteristics of the extracted fluids, that it is possible to find a non-deposition zone which will permit the drilling of wells without a scaling problem.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17242744','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17242744"><span>Heterogeneous conversion of <span class="hlt">calcite</span> aerosol by nitric acid.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Preszler Prince, A; Grassian, V H; Kleiber, P; Young, M A</p> <p>2007-02-07</p> <p>The reaction of nitric acid with <span class="hlt">calcite</span> aerosol at varying relative humidities has been studied under suspended particle conditions in an atmospheric reaction chamber using infrared absorption spectroscopy. The reactant concentration in the chamber, as well as the appearance of gas phase products and surface adsorbed species, was spectroscopically monitored before and after mixing with CaCO(3) (<span class="hlt">calcite</span>) particles. The interaction with HNO(3) was found to lead to gas phase CO(2) evolution and increased water uptake due to heterogeneous conversion of the carbonate to particulate nitrate. The reaction was enhanced as the relative humidity of the system was increased, especially at relative humidities above the reported deliquescence point of particulate Ca(NO(3))(2). The measured reaction extent demonstrates that the total <span class="hlt">calcite</span> particulate mass is available for reaction with HNO(3) and the conversion process is not limited to the particle surface. The spectroscopy of the surface formed nitrate suggests a highly concentrated solution environment with a significant degree of ion pairing. The implications of the HNO(3) loss and the formation of the particulate nitrate product for atmospheric chemistry are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GeCoA.123..351V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GeCoA.123..351V"><span>Earthworm-produced <span class="hlt">calcite</span> granules: A new terrestrial palaeothermometer?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Versteegh, Emma A. A.; Black, Stuart; Canti, Matthew G.; Hodson, Mark E.</p> <p>2013-12-01</p> <p>In this paper we show for the first time that <span class="hlt">calcite</span> granules, produced by the earthworm Lumbricus terrestris, and commonly recorded at sites of archaeological interest, accurately reflect temperature and soil water δ18O values. Earthworms were cultivated in an orthogonal combination of two different (granule-free) soils moistened by three types of mineral water and kept at three temperatures (10, 16 and 20 °C) for an acclimatisation period of three weeks followed by transfer to identical treatments and cultivation for a further four weeks. Earthworm-secreted <span class="hlt">calcite</span> granules were collected from the second set of soils. δ18O values were determined on individual <span class="hlt">calcite</span> granules (δ18Oc) and the soil solution (δ18Ow). The δ18Oc values reflect soil solution δ18Ow values and temperature, but are consistently enriched by 1.51 (± 0.12)‰ in comparison to equilibrium in synthetic carbonates. The data fit the equation 1000 ln α = [20.21 ± 0.92] (103 T-1) - [38.58 ± 3.18] (R2 = 0.95; n = 96; p < 0.0005). As the granules are abundant in modern soils, buried soils and archaeological contexts, and can be dated using U-Th disequilibria, the developed palaeotemperature relationship has enormous potential for application to Holocene and Pleistocene time intervals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004JCrGr.267..635K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004JCrGr.267..635K"><span>Effect of trace lanthanum ion on dissolution and <span class="hlt">crystal</span> growth of calcium carbonate</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kamiya, Natsumi; Kagi, Hiroyuki; Tsunomori, Fumiaki; Tsuno, Hiroshi; Notsu, Kenji</p> <p>2004-07-01</p> <p>Impurity effects of trace lanthanum ion (La 3+) on the dissolution and growth of calcium carbonate were studied with in situ observation techniques. Dissolution kinetics of two polymorphs of calcium carbonate, <span class="hlt">calcite</span> and vaterite, were investigated by monitoring the pH in the solution with laser-induced fluorescence spectroscopy using a pH-sensitive reagent, seminaphthorhodafluors. No effect on dissolution of vaterite was observed with the spectroscopic observations, whereas <span class="hlt">calcite</span> dissolution was significantly inhibited by lanthanum ion with concentrations higher than 1 μM. <span class="hlt">Crystal</span> growth and dissolution processes of <span class="hlt">calcite</span> under the lanthanum-doped condition were observed by means of atomic force microscopy. Step propagations during <span class="hlt">crystal</span> growth and dissolution of <span class="hlt">calcite</span> were inhibited by trace lanthanum ion (5 μM). An insoluble thin layer of lanthanum carbonate deposited on the step site of the <span class="hlt">calcite</span> surface could be a possible cause of the inhibitions observed both for dissolution and growth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1981JCrGr..53...10K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1981JCrGr..53...10K"><span><span class="hlt">Crystal</span> growth of calcium phosphates - epitaxial considerations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Koutsoukos, P. G.; Nancollas, G. H.</p> <p>1981-05-01</p> <p>The growth of one crystalline phase on the surface of another that offers a good <span class="hlt">crystal</span> lattice match, may be important in environmental, physiological and pathological mineralization processes. The epitaxial relationships and kinetics of growth of hydroxyapatite on <span class="hlt">crystals</span> of dicalcium phosphate dihydrate, calcium fluoride and <span class="hlt">calcite</span> have been studied at sustained low supersaturation with respect to hydroxyapatite. At the very low supersaturations, the <span class="hlt">crystallization</span> of hydroxyapatite takes place without the formation of precursor phases. The experimental results are in agreement with theoretical predictions for epitaxial growth, while the kinetics of hydroxyapatite <span class="hlt">crystallization</span> on the foreign substrates is the same as that for the growth of hydroxyapatite on synthetic hydroxyapatite <span class="hlt">crystals</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014Litho.198..281D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014Litho.198..281D"><span>Origin of gem corundum in <span class="hlt">calcite</span> marble: The Revelstoke occurrence in the Canadian Cordillera of British Columbia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dzikowski, Tashia J.; Cempírek, Jan; Groat, Lee A.; Dipple, Gregory M.; Giuliani, Gaston</p> <p>2014-06-01</p> <p>The <span class="hlt">calcite</span> marble-hosted gem corundum (ruby, sapphire) occurrence near Revelstoke, British Columbia, Canada, occurs in the Monashee Complex of the Omineca Belt of the Canadian Cordillera. Corundum occurs in thin, folded and stretched layers with green muscovite + Ba-bearing K-feldspar + anorthite (An0.85-1) ± phlogopite ± Na-poor scapolite. Other silicate layers within the marble are composed of: (1) diopside + tremolite ± quartz and (2) garnet (Alm0.7-0.5Grs0.2-0.4) + Na-rich scapolite + diopside + tremolite + Na,K-amphiboles. Non-silicate layers in the marble are either magnetite- or graphite-bearing. Predominantly pink (locally red or purple) opaque to transparent corundum <span class="hlt">crystals</span> have elevated Cr2O3 (≤ 0.21 wt.%) and variable amounts of TiO2; rare blue rims on the corundum <span class="hlt">crystals</span> contain higher amounts of TiO2 (≤ 0.53 wt.%) and Fe2O3 (≤ 0.07 wt.%). The associated micas have elevated Cr, V, Ti, and Ba contents. Petrography of the silicate layers show that corundum formed from muscovite at the peak of metamorphism (~ 650-700 °C at 8.5-9 kbar). Because the marble is almost pure <span class="hlt">calcite</span> (dolomite is very rare), the corundum was preserved because it did not react with dolomite to spinel + <span class="hlt">calcite</span> during decompression. The scapolite-bearing assemblages formed during or after decompression of the rock at ~ 650 °C and 4-6 kbar. Gem-quality corundum <span class="hlt">crystals</span> formed especially on borders of the mica-feldspar layers in an assemblage with <span class="hlt">calcite</span>. Whole rock geochemistry data show that the corundum-bearing silicate (mica-feldspar) layers formed by mechanical mixing of carbonate with the host gneiss protolith; the bulk composition of the silicate layers was modified by Si and Fe depletion during prograde metamorphism. High element mobility is supported by the homogenization of δ18O and δ13C values in carbonates and silicates for the marble and silicate layers. The silicate layers and the gneiss contain elevated contents of Cr and V due to the volcanoclastic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1810206B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1810206B"><span>Stable isotope (C, O) and monovalent cation fractionation upon synthesis of carbonate-bearing hydroxyl apatite (CHAP) via <span class="hlt">calcite</span> transformation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Böttcher, Michael E.; Schmiedinger, Iris; Wacker, Ulrike; Conrad, Anika C.; Grathoff, Georg; Schmidt, Burkhard; Bahlo, Rainer; Gehlken, Peer-L.; Fiebig, Jens</p> <p>2016-04-01</p> <p>Carbonate-bearing hydroxyl-apatite (CHAP) is of fundamental and applied interest to the (bio)geochemical, paleontological, medical and material science communities, since it forms the basic mineral phase in human and animal teeth and bones. In addition, it is found in non-biogenic phosphate deposits. The stable isotope and foreign element composition of biogenic CHAP is widely used to estimate the formation conditions. This requires careful experimental calibration under well-defined boundary conditions. Within the DFG project EXCALIBOR, synthesis of carbonate-bearing hydroxyapatite was conducted via the transformation of synthetic <span class="hlt">calcite</span> powder in aqueous solution as a function of time, pH, and temperature using batch-type experiments. The aqueous solution was analyzed for the carbon isotope composition of dissolved inorganic carbonate (gas irmMS), the oxygen isotope composition of water (LCRDS), and the cationic composition. The solid was characterized by powder X-ray diffraction, micro Raman and FTIR spectroscopy, SEM-EDX, elemental analysis (EA, ICP-OES) and gas irmMS. Temperature was found to significantly impact the transformation rate of <span class="hlt">calcite</span> to CHAP. Upon complete transformation, CHAP was found to contain up to 5% dwt carbonate, depending on the solution composition (e.g., pH), both incorporated on the A and B type position of the <span class="hlt">crystal</span> lattice. The oxygen isotope fractionation between water and CHAP decreased with increasing temperature with a tentative slope shallower than those reported in the literature for apatite, <span class="hlt">calcite</span> or aragonite. In addition, the presence of dissolved NH4+, K+ or Na+ in aqueous solution led to partial incorporation into the CHAP lattice. How these distortions of the <span class="hlt">crystal</span> lattice may impact stable isotope discrimination is subject of future investigations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5532821','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5532821"><span>Interaction of copper with the surface of <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Franklin, M.L.; Morse, J.W.</p> <p>1981-12-01</p> <p>The interaction of Cu ions in solution with the surface of <span class="hlt">calcite</span> has been studied in a range of solutions from pure water to seawater. Observations of the uptake of Cu from solution onto <span class="hlt">calcite</span> indicates that the process is rapid and strong in both distilled water and seawater. In distilled water, Cu uptake is directly proportional to the concentration of Cu in solution; Cu/sub s/ = K/sub s/Cu/sub 1/. The average value for K/sub s/ is 3.5 +- 1.7. The Cu/sub s/ dependence on Cu/sub 1/ is linear over the entire Cu concentration range studied (0.1 to 200 ..mu..M). Results do not indicate the formation of a precipitate of either malachite or copper carbonate. A precipitate of the form Cu/sub x/Ca/sub 1-x/CO/sub 3/ may be deposited onto the <span class="hlt">calcite</span> surface in distilled water. The value of K/sub s/ in distilled water decreased sharply over the solid to solution ratio range of 0.1 to 2 g CaCO/sub 3/ 1/sup -1/. This was followed by a small change in K/sub s/ for solid to solution ratios in the range of 2 to 10 g CaCO/sub 3/ 1/sup -1/. In seawater, the uptake of Cu is also directly proportional to the concentration of Cu/sub 1/ up to a limiting value of approximately 13 ..mu..M. The average value for K/sub s/ in seawater, 0.24 +- 0.06 (Cu/sub 1/ less than or equal to 13 ..mu..M), is approximately an order of magnitude less than in distilled water. This is probably the result of smaller Cu/sub 1/ activity coefficients and increased site competition by other ions in seawater. Attempts to increase the Cu/sub 1/ concentration above 13 ..mu..M resulted in the additional Cu being deposited on the surface of the <span class="hlt">calcite</span>. A possible explanation for this behavior is the formation of a precipitate of malachite on the <span class="hlt">calcite</span> surface. The value of K/sub s/ decreased slightly with increasing solid to solution ratios in seawater.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1019148','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1019148"><span>Temperature Dependence of the Structural Parameters in the Transformation of Aragonite to <span class="hlt">Calcite</span>, as Determined from In Situ Synchrotron Powder X-ray-Diffratction Data</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Antao, Sytle M.; Hassan, Ishmael</p> <p>2011-09-06</p> <p>The temperature dependency of the <span class="hlt">crystal</span> structure and the polymorphic transition of CaCO{sub 3} from aragonite to <span class="hlt">calcite</span> were studied using Rietveld structure refinement and high-temperature in situ synchrotron powder X-ray-diffraction data at ambient pressure, P. The orthorhombic metastable aragonite at room P, space group Pmcn, transforms to trigonal <span class="hlt">calcite</span>, space group R{bar 3}c, at about T{sub c} = 468 C. This transformation occurs rapidly; it starts at about 420 C and is completed by 500 C, an 80 C interval that took about 10 minutes using a heating rate of 8 C/min. Structurally, from aragonite to <span class="hlt">calcite</span>, the distribution of the Ca atom changes from approximately hexagonal to cubic close-packing. A 5.76% discontinuous increase in volume accompanies the reconstructive first-order transition. Besides the change in coordination of the Ca atom from nine to six from aragonite to <span class="hlt">calcite</span>, the CO{sub 3} groups change by a 30{sup o} rotation across the transition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19911801','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19911801"><span>Biomimetic mineralization of CaCO3 on a phospholipid monolayer: from an amorphous calcium carbonate precursor to <span class="hlt">calcite</span> via vaterite.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Xiao, Junwu; Wang, Zhining; Tang, Yecang; Yang, Shihe</p> <p>2010-04-06</p> <p>A phospholipid monolayer, approximately half the bilayer structure of a biological membrane, can be regarded as an ideal model for investigating biomineralization on biological membranes. In this work on the biomimetic mineralization of CaCO(3) under a phospholipid monolayer, we show the initial heterogeneous nucleation of amorphous calcium carbonate precursor (ACC) nanoparticles at the air-water interface, their subsequent transformation into the metastable vaterite phase instead of the most thermodynamically stable <span class="hlt">calcite</span> phase, and the ultimate phase transformation to <span class="hlt">calcite</span>. Furthermore, the spontaneity of the transformation from vaterite to <span class="hlt">calcite</span> was found to be closely related to the surface tension; high surface pressure could inhibit the process, highlighting the determinant of surface energy. To understand better the mechanisms for ACC formation and the transformation from ACC to vaterite and to <span class="hlt">calcite</span>, in situ Brewster angle microscopy (BAM), ex situ scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray diffraction analysis were employed. This work has clarified the <span class="hlt">crystallization</span> process of calcium carbonate under phospholipid monolayers and therefore may further our understanding of the biomineralization processes induced by cellular membranes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28063520','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28063520"><span>Zeta potential of artificial and natural <span class="hlt">calcite</span> in aqueous solution.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Al Mahrouqi, Dawoud; Vinogradov, Jan; Jackson, Matthew D</p> <p>2017-02-01</p> <p>Despite the broad range of interest and applications, controls on <span class="hlt">calcite</span> surface charge in aqueous solution, especially at conditions relevant to natural systems, remain poorly understood. The primary data source to understand <span class="hlt">calcite</span> surface charge comprises measurements of zeta potential. Here we collate and review previous measurements of zeta potential on natural and artificial <span class="hlt">calcite</span> and carbonate as a resource for future studies, compare and contrast the results of these studies to determine key controls on zeta potential and where uncertainties remain, and report new measurements of zeta potential relevant to natural subsurface systems. The results show that the potential determining ions (PDIs) for the carbonate mineral surface are the lattice ions Ca(2+), Mg(2+) and CO3(2-). The zeta potential is controlled by the concentration-dependent adsorption of these ions within the Stern layer, primarily at the Outer Helmholtz Plane (OHP). Given this, the Iso-Electric Point (IEP) at which the zeta potential is zero should be expressed as pCa (or pMg). It should not be reported as pH, similar to most metal oxides. The pH does not directly control the zeta potential. Varying the pH whilst holding pCa constant yields constant zeta potential. The pH affects the zeta potential only by moderating the equilibrium pCa for a given CO2 partial pressure (pCO2). Experimental studies that appear to yield a systematic relationship between pH and zeta potential are most likely observing the relationship between pCa and zeta potential, with pCa responding to the change in pH. New data presented here show a consistent linear relationship between equilibrium pH and equilibrium pCa or pMg irrespective of sample used or solution ionic strength. The surface charge of <span class="hlt">calcite</span> is weakly dependent on pH, through protonation and deprotonation reactions that occur within a hydrolysis layer immediately adjacent to the mineral surface. The Point of Zero Charge (PZC) at which the surface</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016BGeo...13.6487K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016BGeo...13.6487K"><span>Carbonate "clumped" isotope signatures in aragonitic scleractinian and <span class="hlt">calcitic</span> gorgonian deep-sea corals</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kimball, Justine; Eagle, Robert; Dunbar, Robert</p> <p>2016-12-01</p> <p> between the corals of different mineralogy is in the same direction as published theoretical predictions for the offset between <span class="hlt">calcite</span> and aragonite although the magnitude of the offset is different. One possibility is that the deep-sea coral results reflect high-Mg and aragonite <span class="hlt">crystals</span> attaining nominal mineral equilibrium clumped isotope signatures due to conditions of extremely slow growth. In that case, a possible explanation for the attainment of disequilibrium bulk isotope signatures and equilibrium clumped isotope signatures by deep-sea corals is that extraordinarily slow growth rates can promote the occurrence of isotopic reordering in the interfacial region of growing <span class="hlt">crystals</span>. We also cannot rule out a component of a biological "vital effect" influencing clumped isotope signatures in one or both orders of coral. Based on published experimental data and theoretical calculations, these biological vital effects could arise from kinetic isotope effects due to the source of carbon used for calcification, temperature- and pH-dependent rates of CO2 hydration and/or hydroxylation, calcifying fluid pH, the activity of carbonic anhydrase, the residence time of dissolved inorganic carbon in the calcifying fluid, and calcification rate. A third possible explanation is the occurrence of variable acid digestion fractionation factors. Although a recent study has suggested that dolomite, <span class="hlt">calcite</span>, and aragonite may have similar clumped isotope acid digestion fractionation factors, the influence of acid digestion kinetics on Δ47 is a subject that warrants further investigation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1335183-carbonate-clumped-isotope-signatures-aragonitic-scleractinian-calcitic-gorgonian-deep-sea-corals','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1335183-carbonate-clumped-isotope-signatures-aragonitic-scleractinian-calcitic-gorgonian-deep-sea-corals"><span>Carbonate “clumped” isotope signatures in aragonitic scleractinian and <span class="hlt">calcitic</span> gorgonian deep-sea corals</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Kimball, Justine; Eagle, Robert; Dunbar, Robert</p> <p>2016-12-12</p> <p> calibrations. The offset between the corals of different mineralogy is in the same direction as published theoretical predictions for the offset between <span class="hlt">calcite</span> and aragonite although the magnitude of the offset is different. One possibility is that the deep-sea coral results reflect high-Mg and aragonite <span class="hlt">crystals</span> attaining nominal mineral equilibrium clumped isotope signatures due to conditions of extremely slow growth. In that case, a possible explanation for the attainment of disequilibrium bulk isotope signatures and equilibrium clumped isotope signatures by deep-sea corals is that extraordinarily slow growth rates can promote the occurrence of isotopic reordering in the interfacial region of growing <span class="hlt">crystals</span>. We also cannot rule out a component of a biological “vital effect” influencing clumped isotope signatures in one or both orders of coral. Based on published experimental data and theoretical calculations, these biological vital effects could arise from kinetic isotope effects due to the source of carbon used for calcification, temperature- and pH-dependent rates of CO2 hydration and/or hydroxylation, calcifying fluid pH, the activity of carbonic anhydrase, the residence time of dissolved inorganic carbon in the calcifying fluid, and calcification rate. A third possible explanation is the occurrence of variable acid digestion fractionation factors. Although a recent study has suggested that dolomite, <span class="hlt">calcite</span>, and aragonite may have similar clumped isotope acid digestion fractionation factors, the influence of acid digestion kinetics on Δ47 is a subject that warrants further investigation.« less</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015BGD....1219115K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015BGD....1219115K"><span>Carbonate "clumped" isotope signatures in aragonitic scleractinian and <span class="hlt">calcitic</span> gorgonian deep-sea corals</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kimball, J.; Tripati, R. E.; Dunbar, R.</p> <p>2015-12-01</p> <p> corals of different mineralogy is in the same direction as published theoretical predictions for the offset between <span class="hlt">calcite</span> and aragonite, although the magnitude of the offset is different. One possibility is that the deep-sea coral results reflect that <span class="hlt">crystals</span> may attain nominal mineral equilibrium clumped isotope signatures only under conditions of extremely slow growth. In that case, a possible explanation for the attainment of disequilibrium bulk isotope signatures and equilibrium clumped isotope signatures by deep-sea corals is that extraordinarily slow growth rates can promote the occurrence of isotopic reordering in the interfacial region of growing <span class="hlt">crystals</span>. We also cannot rule out a component of a biological "vital-effect" influencing clumped isotope signatures in one or both orders of coral. Based on published experimental data and theoretical calculations, these biological "vital" effects could arise from kinetic isotope effects due to the source of carbon used for calcification, temperature- and pH-dependent rates of CO2 hydration and/or hydroxylation, calcifying fluid pH, the activity of carbonic anhydrase, the residence time of dissolved inorganic carbon in the calcifying fluid, and calcification rate. A third possible explanation is the occurrence of variable acid digestion fractionation factors. Although a recent study has suggested that dolomite, <span class="hlt">calcite</span>, and aragonite may have similar clumped isotope acid digestion fractionation factors, the influence of acid digestion kinetics on Δ47 is a subject that warrants further investigation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFMPP33A..04B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFMPP33A..04B"><span>Interrogating coccolith <span class="hlt">calcite</span>: paleoceanographic proxy data from nannofractions, foraminifera and single coccolith specimens</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bown, P. R.; Lees, J. A.; Young, J.; Robinson, S. A.; MacLeod, K. G.; Grocke, D. R.; Schmidt, D. N.; Hinton, R.</p> <p>2009-12-01</p> <p>Nannofossils are the calcareous cell-wall coverings of oceanic phytoplankton and the most abundant but smallest routinely studied fossil group. Small size (typically <8 microns and <400 pg of <span class="hlt">calcite</span> per lith) has limited their use as geochemical proxies because it is difficult to separate them by mechanical picking or using centrifuge or filtration techniques. However, the <63µm fraction of marine sediments is often implied to represent the bulk nannofossil signal in geochemical studies, but actually represents a spectrum of oceanic carbonate, from parts of larger organisms (potentially benthic, nektonic and planktonic) to micarb (of unknown, possibly non-biological, origin), consequently obfuscating the true nannofossil signal. Additionally, it is known that certain nannofossil taxa are more responsive to paleoenvironmental change than others, and so a bulk nannofossil signal is potentially misleading. Consequently, there has been a strong incentive to develop techniques that overcome these difficulties, as coccoliths represent a potentially invaluable and inexhaustible geochemical archive of paleoenvironmental information. Most importantly, coccoliths are hugely abundant in marine sediments deposited above the <span class="hlt">calcite</span> compensation depth (billions of specimens per gram) and their chemical composition is resistant to the modifying effects of diagenesis since they are relatively non-porous structures formed from a small number of solid <span class="hlt">calcite</span> <span class="hlt">crystals</span>. Here we compare a range of paleoceanographic geochemical proxies (element ratios, stable isotopes) measured from (a) bulk sediment, single foraminifers and sieved near-monotaxic nannofossil fractions using wet chemistry and (b) single coccolith specimens using an ion microprobe SIMS. The data come from the PETM interval of ODP Leg 207 Site 1259 (Demerara Rise, western equatorial Atlantic) and enable comparisons between paleontological, assemblage-based productivity proxies and geochemical proxies based on</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFM.T42D..07G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFM.T42D..07G"><span>Nanoindentation Creep of Quartz, Olivine, and <span class="hlt">Calcite</span>, with Implications for Rate and State Friction Laws</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Goldsby, D. L.; Rar, A.; Pharr, G. M.; Tullis, T. E.</p> <p>2003-12-01</p> <p>A hallmark observation from friction experiments on rocks is that the coefficient of friction increases linearly with the log of time of quasi-stationary contact. This increase in friction, or state in the rate- and state-variable friction laws, is usually attributed to an increase in real area of contact between rough surfaces caused by deformation of highly stressed contacts. This behavior is typically explored in slide-hold-slide (SHS) friction experiments at ambient temperature. Despite the importance of the evolution of the state variable for determining conditions for which earthquakes may nucleate, contact-scale deformation mechanisms in rocks remain unknown. In an effort to identify these deformation mechanisms, nanoindentation creep experiments were conducted on single <span class="hlt">crystals</span> of quartz, olivine and <span class="hlt">calcite</span> at room temperature and constant loads of 50 to 250 mN. The amount of creep in a typical nanoindentation creep test is indicated by the increase in indentation area with time, determined from the measured displacement of indenter into the specimen and the well-characterized geometry of the indenter tip. A major limitation of such tests, that displacements are difficult to discern from thermal noise, was eliminated by employing continuous stiffness techniques. A 45-Hz oscillation in displacement of 2 nm amplitude was imposed on a diamond Berkovich indenter held at otherwise constant load for times comparable to those in SHS tests, up to 5x104 s. By analyzing the resulting specimen response with a frequency-specific analyzer, a nearly continuous measure of the contact stiffness, proportional to contact area, was obtained. Thus, contact area is determined over times too short for significant thermal drift. Changes in area with time from indentation tests were compared with those inferred from complementary SHS tests on quartz, olivine and <span class="hlt">calcite</span> rocks conducted in a high pressure rotary-shear apparatus. The contact area between indenter and specimen</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeCoA.193..119B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeCoA.193..119B"><span>First-principles study of boron speciation in <span class="hlt">calcite</span> and aragonite</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Balan, Etienne; Pietrucci, Fabio; Gervais, Christel; Blanchard, Marc; Schott, Jacques; Gaillardet, Jérome</p> <p>2016-11-01</p> <p>Despite the importance of boron as a proxy of past ocean pH, the <span class="hlt">crystal</span>-chemical factors controlling its incorporation in the structure of calcium carbonates are still poorly understood. This is partly linked to an imperfect knowledge of the coordination, protonation state and local environment of boron species in these minerals. In the present study, we use first-principles quantum mechanical tools to model selected trigonal and tetragonal boron species in <span class="hlt">calcite</span> and aragonite. The stable geometry of the models is obtained from standard energy minimization schemes or using a more advanced metadynamics exploration of their configurational space. The computation of 11B NMR chemical shifts and quadrupolar coupling parameters enables a straightforward comparison of the models to existing experimental NMR data. The results show that B in calcium carbonates does occur as structural species substituted for CO32- anions. The B speciation depends on the polymorph considered. In <span class="hlt">calcite</span>, structural boron is present as partially deprotonated trigonal BO2(OH)2- species coexisting with a fraction of substituted B(OH)4- groups. In aragonite, the B(OH)4- substitution for CO32- anions is dominant. Different species, including entrapped B(OH)3 molecules and substituted BO33- groups also occur in biogenic samples. The diversity of B speciation reflects a diversity of B incorporation mechanisms and sheds light on previous studies confronting B isotopic composition determination with NMR observations. The mechanisms of boron incorporation in calcium carbonates are probably more complex than usually assumed in the literature using boron isotopes as a proxy of paleo-atmospheric CO2 reconstructions. Although not invalidating the empirical paleo-pH proxy, these results call for a better understanding of the fundamental mechanisms of boron incorporation in carbonates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005Tectp.402..153C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005Tectp.402..153C"><span><span class="hlt">Calcite</span> strains, kinematic indicators, and magnetic flow fabric of a Proterozoic pseudotachylyte swarm, Minnesota River valley, USA</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Craddock, John P.; Magloughlin, Jerry F.</p> <p>2005-06-01</p> <p>Near Granite Falls, Minnesota sub-parallel pseudotachylyte, mafic dikes, and <span class="hlt">calcite</span> veins crosscut Archean granulite facies rocks in the Minnesota River valley adjacent to the north-dipping Yellow Medicine Shear Zone (YMSZ; N80°E) that separates the Montevideo and Morton tectonic terranes. The docking of these two Archean terranes occurred prior to intrusion of the 2.067 Ga Kenora-Kabetogama dike swarm as demonstrated by aeromagnetic anomalies (correlated with field exposures) that cross the YMSZ without offset. Tectonic adjustments along the YMSZ associated with the Penokean Orogeny (˜ 1.8 Ga) are likely responsible for pseudotachylyte formation. Pseudotachylyte is exposed in 22 sub-parallel veins (˜ N80°E, 90°) each less than 2 cm wide across an outcrop width of 45 m. The pseudotachylyte matrix is commonly banded, and contains <span class="hlt">crystal</span> fragments (quartz, plagioclase, amphibole, rutile, apatite, ilmenite, ulvöspinel), magnetite microlites, flow banding swirls, amygdules (filled with <span class="hlt">calcite</span>, ankerite and siderite), collapsed vesicles, and abundant lithic clasts. Pseudotachylyte formed in a number of phases. Kinematic reconstruction is complex, utilizing winged porphyroclasts, S-C structures in the country rock, and fault drag indicators along the pseudotachylyte zones. Dextral motion along the YMSZ is the most common observation. Mechanically twinned <span class="hlt">calcite</span> within amygdules in the pseudotachylyte preserves horizontal shortening normal to the pseudotachylyte strike. <span class="hlt">Calcite</span> veins are apparently contemporaneous with the pseudotachylyte; one set preserves twinning strains identical to the <span class="hlt">calcite</span> amygdule strains, and the second set contains a horizontal, vein-parallel (N70°E) shortening strain. The pseudotachylyte contains a flow fabric, as determined by AMS techniques, that is a proxy for vertical flow ( Kmax is vertical). The Kenora-Kabetogama dikes, identified geochemically, are locally parallel to the pseudotachylyte and the adjacent YMSZ tectonic suture</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70010877','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70010877"><span>The sensitized luminescence of manganese-activated <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Schulman, J.H.; Evans, L.W.; Ginther, R.J.; Murata, K.J.</p> <p>1947-01-01</p> <p>Synthetic manganese-activated <span class="hlt">calcites</span> are shown to be practically inert to ultraviolet excitation in the range 2000-3500A, while they are luminescent under cathode-ray excitation. The incorporation of small amounts of an auxiliary impurity along with the manganese produces the strong response to ultraviolet radiation hitherto ascribed to CaCO3:Mn itself. Three such impurities have been studied: lead, thallium, and cerium. The first two induce excitation in the neighborhood of the mercury resonance line, while the cerium introduces a response principally to longer wave ultraviolet. The strong response to 2537A excitation shown by some natural <span class="hlt">calcites</span> is likewise found to be due to the presence of lead along with the manganese, rather than to the manganese alone. The data do not warrant ascribing the longer wave-length ultraviolet-excited luminescence of all natural <span class="hlt">calcites</span> to the action of an auxiliary impurity. The essential identity of the cathode-ray excited luminescence spectra of CaCO 3:Mn, CaCO3: (Pb+Mn), CaCO3:(Tl+Mn), and CaCO3:(Ce+Mn) with the 2537A-excited spectra of the latter three is evidence that the luminescent center in all cases is the manganese ion or the MnO6 group. It is shown that a "cascade" mechanism for the action of the auxiliary impurities, lead, thallium, and cerium, is incorrect; and that the phenomenon must be considered as a case of sensitized luminescence. Owing to the nature of cathode-ray excitation, the manganese activator can be excited by this agent even in the absence of a second impurity. For optical excitation, however, an absorption band for the ultraviolet must be established by building into the CaCO3:Mn a second impurity or "sensitizer.".</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4105460','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4105460"><span>Principles of <span class="hlt">Calcite</span> Dissolution in Human and Artificial Otoconia</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Walther, Leif Erik; Blödow, Alexander; Buder, Jana; Kniep, Rüdiger</p> <p>2014-01-01</p> <p>Human otoconia provide mechanical stimuli to deflect hair cells of the vestibular sensory epithelium for purposes of detecting linear acceleration and head tilts. During lifetime, the volume and number of otoconia are gradually reduced. In a process of degeneration morphological changes occur. Structural changes in human otoconia are assumed to cause vertigo and balance disorders such as benign paroxysmal positional vertigo (BPPV). The aim of this study was to investigate the main principles of morphological changes in human otoconia in dissolution experiments by exposure to hydrochloric acid, EDTA, demineralized water and completely purified water respectively. For comparison reasons artificial (biomimetic) otoconia (<span class="hlt">calcite</span> gelatin nanocomposits) and natural <span class="hlt">calcite</span> were used. Morphological changes were detected in time steps by the use of environmental scanning electron microscopy (ESEM). Under in vitro conditions three main dissolution mechanisms were identified as causing characteristic morphological changes of the specimen under consideration: pH drops in the acidic range, complex formation with calcium ions and changes of ion concentrations in the vicinity of otoconia. Shifts in pH cause a more uniform reduction of otoconia size (isotropic dissolution) whereas complexation reactions and changes of the ionic concentrations within the surrounding medium bring about preferred attacks at specific areas (anisotropic dissolution) of human and artificial otoconia. Owing to successive reduction of material, all the dissolution mechanisms finally produce fragments and remnants of otoconia. It can be assumed that the organic component of otoconia is not significantly attacked under the given conditions. Artificial otoconia serve as a suitable model system mimicking chemical attacks on biogenic specimens. The underlying principles of <span class="hlt">calcite</span> dissolution under in vitro conditions may play a role in otoconia degeneration processes such as BPPV. PMID:25048115</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/584984','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/584984"><span>Top-<span class="hlt">seed</span> solution growth and characterization of AlSb single <span class="hlt">crystals</span> for gamma-ray detectors. Final report, 1 October 1994--30 September 1995</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Witt, A.F.; Becla, P.; Counterman, C.; DiFrancesco, J.; Landahl, G.; Morse, K.; Sanchez, J.</p> <p>1996-01-26</p> <p>The ultimate objective of the conducted research is to ascertain the potential of AlSb (in single <span class="hlt">crystal</span> form) for application as {gamma}-detector material operating at room temperature. To this end approaches to <span class="hlt">crystal</span> growth were to be developed which permit control of growth parameters affecting critical application specific properties of AlSb. The research was focused on exploration of the effectiveness of the Czochralski method and on the development of methods and procedures leading to AlSb <span class="hlt">crystals</span> with low free carrier concentration and a high mobility-lifetime product. Conventional melt growth of AlSb by the Czochralski technique (from stoichiometric charges) generally yielded material with high net carrier concentrations and low mobility-lifetime products. Significant improvement in <span class="hlt">crystal</span> properties was achieved, when operating with non-stoichiometric melts, containing Sb in excess at levels of 3 to 10 mol%, further improvements were obtained when changing ambient argon pressure from atmospheric to 300 psi, and using high purity alumina crucibles which were inductively heated with a graphite susceptor CVD coated with silicon-carbide. Initial efforts to reduce evaporative loss of Sb through application of the LEC technique (liquid encapsulated Czochralski) with conventional encapsulants (B{sub 2}O{sub 3}, LiF, CaF{sub 2}) failed because of their interaction with the crucible and the AlSb melt. Compensation techniques (based on extrinsic doping) were found to lead to the desired reduction of free carriers in AlSb. Such material, however, exhibits a significant decrease of charge carrier mobility and lifetime. Early termination of this research program prevented optimization of critical materials properties in AlSb and precluded at this time a realistic assessment of the potential of this material for solid state detector applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6568348','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6568348"><span><span class="hlt">Calcite</span> dissolution: an in situ study in the Panama Basin</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Thunell, R.C.; Keir, R.S.; Honjo, S.</p> <p>1981-05-08</p> <p>The results of an in situ study of <span class="hlt">calcite</span> dissolution in the Panama Basin indicate that the rate of dissolution in the water column increases suddenly below a water depth of about 2800 meters. This coincides with the depth at which the calcium carbonate content of surface sediments begins to decrease rapidly or the sedimentary lysocline. Since this level of increased dissolution both in the water column and on the sea floor does not appear to be related to the transition from supersaturation to undersaturation with respect to carbonate, there may be a kinetic origin for the lysocline in this region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17739398','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17739398"><span><span class="hlt">Calcite</span> Dissolution: An in situ Study in the Panama Basin.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Thunell, R C; Keir, R S; Honjo, S</p> <p>1981-05-08</p> <p>The results of an in situ study of <span class="hlt">calcite</span> dissolution in the Panama Basin indicate that the rate of dissolution in the water column increases suddenly below a water depth of about 2800 meters. This coincides with the depth at which the calcium carbonate content of surface sediments begins to decrease rapidly or the sedimentary lysocline. Since this level of increased dissolution both in the water column and on the sea floor does not appear to be related to the transition from supersaturation to undersaturation with respect to carbonate, there may be a kinetic origin for the lysocline in this region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/866352','DOE-PATENT-XML'); return false;" href="http://www.osti.gov/scitech/servlets/purl/866352"><span>String stabilized ribbon growth a method for <span class="hlt">seeding</span> same</span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Sachs, Emanuel M.</p> <p>1987-08-25</p> <p>This invention is a method of initiating or <span class="hlt">seeding</span> the growth of a crystalline or polycrystalline ribbon by the String Stabilized Ribbon Growth Method. The method for <span class="hlt">seeding</span> the <span class="hlt">crystal</span> growth comprises contacting a melt surface with a <span class="hlt">seed</span> and two strings used in edge stabilization. The wetted strings attach to the wetted <span class="hlt">seed</span> as a result of the freezing of the liquid melt. Upon drawing the <span class="hlt">seed</span>, which is attached to the strings, away from the melt surface a melt liquid meniscus, a <span class="hlt">seed</span> junction, and a growth interface forms. Further pulling of the attached <span class="hlt">seed</span> causes a <span class="hlt">crystal</span> ribbon to grow at the growth interface. The boundaries of the growing ribbon are: at the top the <span class="hlt">seed</span> junction, at the bottom the freezing boundary of the melt liquid meniscus, and at the edges frozen-in strings.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016CoMP..171...65B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016CoMP..171...65B"><span>The evolution of <span class="hlt">calcite</span>-bearing kimberlites by melt-rock reaction: evidence from polymineralic inclusions within clinopyroxene and garnet megacrysts from Lac de Gras kimberlites, Canada</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bussweiler, Y.; Stone, R. S.; Pearson, D. G.; Luth, R. W.; Stachel, T.; Kjarsgaard, B. A.; Menzies, A.</p> <p>2016-07-01</p> <p>Megacrystic (>1 cm) clinopyroxene (Cr-diopside) and garnet (Cr-pyrope) xenocrysts within kimberlites from Lac de Gras (Northwest Territories, Canada) contain fully <span class="hlt">crystallized</span> melt inclusions. These `polymineralic inclusions' have previously been interpreted to form by necking down of melts at mantle depths. We present a detailed petrographical and geochemical investigation of polymineralic inclusions and their host <span class="hlt">crystals</span> to better understand how they form and what they reveal about the evolution of kimberlite melt. Genetically, the megacrysts are mantle xenocrysts with peridotitic chemical signatures indicating an origin within the lithospheric mantle (for the Cr-diopsides studied here ~4.6 GPa, 1015 °C). Textural evidence for disequilibrium between the host <span class="hlt">crystals</span> and their polymineralic inclusions (spongy rims in Cr-diopside, kelyphite in Cr-pyrope) is consistent with measured Sr isotopic disequilibrium. The preservation of disequilibrium establishes a temporal link to kimberlite eruption. In Cr-diopsides, polymineralic inclusions contain phlogopite, olivine, chromite, serpentine, and <span class="hlt">calcite</span>. Abundant fluid inclusion trails surround the inclusions. In Cr-pyropes, the inclusions additionally contain Al-spinel, clinopyroxene, and dolomite. The major and trace element compositions of the inclusion phases are generally consistent with the early stages of kimberlite differentiation trends. Extensive chemical exchange between the host phases and the inclusions is indicated by enrichment of the inclusions in major components of the host <span class="hlt">crystals</span>, such as Cr2O3 and Al2O3. This chemical evidence, along with phase equilibria constraints, supports the proposal that the inclusions within Cr-diopside record the decarbonation reaction: dolomitic melt + diopside → forsterite + <span class="hlt">calcite</span> + CO2, yielding the observed inclusion mineralogy and producing associated (CO2-rich) fluid inclusions. Our study of polymineralic inclusions in megacrysts provides clear mineralogical</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004PhDT........32G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004PhDT........32G"><span>The effect of liquid phase chemistry on growth of lead magnesium niobate-lead titanate single <span class="hlt">crystals</span> by <span class="hlt">seeded</span> polycrystal conversion</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gorzkowski, Edward P., III</p> <p></p> <p>The effect that liquid phase content and chemistry has on single <span class="hlt">crystal</span> growth was investigated in this study. This was accomplished by determining the single <span class="hlt">crystal</span> growth mechanism as well as studying the effect of hot pressing environment. Characterization techniques played a large role in deciphering the relevance of each effect. One such technique was used because x-ray absorption of oxygen is significant in thin specimens of Pb(Mg1/3Nb2/3 )O3-35 mol% PbTiO3 [PMN-35PT] due to the presence of Pb and Nb. Using only XEDS data, the zeta-factor method provides absorption corrected compositional information, which was helpful to fully characterize the liquid phase. It was shown that the compositional data were in very good agreement with the nominal values for PMN-35 PT, whereas the uncorrected data underestimated the oxygen content by 300%. This technique linked the swelling of samples to changes in the oxygen to lead ratio of the excess PbO due to hot-pressing in air. This observation corroborates the microstructural and x-ray diffraction data that was obtained. The influence of excess PbO on {001} single <span class="hlt">crystal</span> growth was studied in the range of 0-10 vol% PbO. It was found that up to 1.5 vol% PbO, the amount of single <span class="hlt">crystal</span> and grain growth increased with increasing PbO additions. At higher PbO contents, however, the growth becomes independent of liquid fraction for all annealing times. In addition since the matrix grains were faceted and the growth best fit parabolic kinetics, interface reaction control was deemed the most likely growth mechanism. It was also shown that the chemistry of the liquid phase was dynamic as characterized in an Analytical Electron Microscope. In fact, MgO was found to precipitate out of the system due the saturation of MgO in the liquid, which in turn altered the liquid/solid surface energy. By changing the energy of the system, the matrix grains become more faceted, i.e. the frequency of {100} surfaces increases. This reduces the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1995GeCoA..59.3087Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1995GeCoA..59.3087Z"><span>Hydrodynamic control of inorganic <span class="hlt">calcite</span> precipitation in Huanglong Ravine, China: Field measurements and theoretical prediction of deposition rates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zaihua, Liu; Svensson, U.; Dreybrodt, W.; Daoxian, Yuan; Buhmann, D.</p> <p>1995-08-01</p> <p>Hydrochemical and hydrodynamical investigations are presented to explain tufa deposition rates along the flow path of the Huanglong Ravine, located in northwestern Sichuan province, China, on an altitude of about 3400 m asl. Due to outgassing of CO 2 the mainly spring-fed stream exhibits, along a valley of 3.5 km, <span class="hlt">calcite</span> precipitation rates up to a few mm/year. We have carried out in situ experiments to measure <span class="hlt">calcite</span> deposition rates at rimstone dams, inside of pools and in the stream-bed. Simultaneously, the downstream evolution of water chemistry was investigated at nine locations with respect to Ca 2+, Mg 2+, Na +, Cl -, SO 42-, and alkalinity. Temperature, pH, and conductivity were measured in situ, while total hardness, Ca T, and alkalinity have been determined immediately after sampling, performing standard titration methods. The water turned out to be of an almost pure CaMgHCO 3 type. The degassing of CO 2 causes high supersaturation with respect to <span class="hlt">calcite</span> and due to <span class="hlt">calcite</span> precipitation the Ca 2+ concentration decreases from 6·10 -3 mole/1 upstream down to 2.5·10 -3 mole/1 at the lower course. Small rectangular shaped tablets of pure marble were mounted under different flow regimes, i.e., at the dam sites with fast water flow as well as inside pools with still water. After the substrate samples had stayed in the water for a period of a few days, the deposition rates were measured by weight increase, up to several tens of milligrams. Although there were no differences in hydrochemistry, deposition rates in fast flowing water were higher by as much as a factor of four compared to still water, indicating a strong influence of hydrodynamics. While upstream rates amounted up to 5 mm/year, lower rates of about 1 mm/year were observed downstream. Inspection of the marble substrate surfaces by EDAX and SEM (scanning electron microscope) revealed authigeneously grown <span class="hlt">calcite</span> <span class="hlt">crystals</span> of about 10 μm. Their shape and habit are indicative of a chemically</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70029040','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70029040"><span>The ubiquitous nature of accessory <span class="hlt">calcite</span> in granitoid rocks: Implications for weathering, solute evolution, and petrogenesis</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>White, A.F.; Schulz, M.S.; Lowenstern, J. B.; Vivit, D.V.; Bullen, T.D.</p> <p>2005-01-01</p> <p><span class="hlt">Calcite</span> is frequently cited as a source of excess Ca, Sr and alkalinity in solutes discharging from silicate terrains yet, no previous effort has been made to assess systematically the overall abundance, composition and petrogenesis of accessory <span class="hlt">calcite</span> in granitoid rocks. This study addresses this issue by analyzing a worldwide distribution of more than 100 granitoid rocks. <span class="hlt">Calcite</span> is found to be universally present in a concentration range between 0.028 to 18.8 g kg-1 (mean = 2.52 g kg-1). <span class="hlt">Calcite</span> occurrences include small to large isolated anhedral grains, fracture and cavity infillings, and sericitized cores of plagioclase. No correlation exists between the amount of <span class="hlt">calcite</span> present and major rock oxide compositions, including CaO. Ion microprobe analyses of in situ <span class="hlt">calcite</span> grains indicate relatively low Sr (120 to 660 ppm), negligible Rb and 87Sr/86Sr ratios equal to or higher than those of coexisting plagioclase. Solutes, including Ca and alkalinity produced by batch leaching of the granitoid rocks (5% CO2 in DI water for 75 d at 25??C), are dominated by the dissolution of <span class="hlt">calcite</span> relative to silicate minerals. The correlation of these parameters with higher <span class="hlt">calcite</span> concentrations decreases as leachates approach thermodynamic saturation. In longer term column experiments (1.5 yr), reactive <span class="hlt">calcite</span> becomes exhausted, solute Ca and Sr become controlled by feldspar dissolution and 87Sr/ 86Sr by biotite oxidation. Some accessory <span class="hlt">calcite</span> in granitoid rocks is related to intrusion into carbonate wall rock or produced by later hydrothermal alteration. However, the ubiquitous occurrence of <span class="hlt">calcite</span> also suggests formation during late stage (subsolidus) magmatic processes. This conclusion is supported by petrographic observations and 87Sr/86Sr analyses. A review of thermodynamic data indicates that at moderate pressures and reasonable CO2 fugacities, <span class="hlt">calcite</span> is a stable phase at temperatures of 400 to 700??C. Copyright ?? 2005 Elsevier Ltd.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA452109','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA452109"><span>A Laboratory Study Investigating the Feasibility of Applying <span class="hlt">Calcite</span>-Type Coatings to Segregated Ballast Tanks</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1981-08-01</p> <p>A LABORATORY STUDY INVESTIGATIING THE FEASIBILITY OF APPLYING <span class="hlt">CALCITE</span> -TYPE COATINGS TO SEGREGATED BALLAST TANKS AUGUST, 1981 Prepared by: Ocean City...Laboratory Study Investigating The Feasibility of Applying <span class="hlt">Calcite</span> -Type Coatings to Segregated Ballast Tanks 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c...Executive Summary List of Figures I. Conclusions II. Introduction III. Background-The Development and Use of <span class="hlt">Calcite</span> -Type Coatings IV. Experimental</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA451914','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA451914"><span>An Investigation of Possible Ways to Enhance the Deposition of <span class="hlt">Calcite</span>-Type Coatings</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1984-01-01</p> <p>AN INVESTIGATION OF POSSIBLE WAYS TO ENHANCE THE DEPOSITION OF <span class="hlt">CALCITE</span> -TYPE COATINGS JANUARY 1984 Prepared by: OCEAN CITY RESEARCH CORP. in...Enhance The Deposition of <span class="hlt">Calcite</span> -Type Coatings 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e...City, New Jersey under the direction of Mr. The research study continued of applying <span class="hlt">calcite</span> -type coatings George A. Gehring, Jr. an to investigation</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17807291','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17807291"><span><span class="hlt">Calcite</span>: rates of dissolution in a vertical profile in the central pacific.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Peterson, M N</p> <p>1966-12-23</p> <p>Rate of dissoluton of calcium carbonate (<span class="hlt">calcite</span>) was determined for a vertical profile 5000 mizeters deep in the central Pacific by measuring the loss of weight of optical <span class="hlt">calcite</span> spheres arrayed on a mooring. Waters of the Pacific are undersaturated in all but the upper several hundred meters. A sharp increase in the rate of dissolution occurs at a depth of about 3700 meters, which corresponds closely to the depth below which <span class="hlt">calcite</span> hias been dissolved from the sediments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21794973','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21794973"><span>Utilization of <span class="hlt">calcite</span> and waste glass for preparing construction materials with a low environmental load.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Maeda, Hirotaka; Imaizumi, Haruki; Ishida, Emile Hideki</p> <p>2011-11-01</p> <p>In this study, porous <span class="hlt">calcite</span> materials are hydrothermally treated at 200 °C using powder compacts consisting of <span class="hlt">calcite</span> and glasses composed of silica-rich soda-lime. After treatment, the glasses are converted into calcium aluminosilicate hydrates, such as zeolite phases, which increase their strength. The porosity and morphology of new deposits of hydrothermally solidified materials depend up on the chemical composition of glass. The use of <span class="hlt">calcite</span> and glass in the hydrothermal treatment plays an important role in the solidification of <span class="hlt">calcite</span> without thermal decomposition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996SedG..105..241K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996SedG..105..241K"><span>Marine diagenesis of Lower Ordovician carbonate sediments (Dumugol Formation), Korea: cementation in a <span class="hlt">calcite</span> sea</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kim, Jeong Chan; Lee, Yong Il</p> <p>1996-09-01</p> <p>The Lower Ordovician Dumugol Formation exhibits many features that indicate early lithification, such as <span class="hlt">calcite</span> nodules, hardgrounds, mud-mounds and intraclasts. Detailed observations of these early-lithified features reveal that rapid marine cementation was instrumental in their formation. Marine lithification took place in a low-energy subtidal environmental that was influenced by intermittent storms. Marine cements include syntaxial overgrowth, bladed <span class="hlt">calcite</span>, fibrous <span class="hlt">calcite</span> and fine-crystalline equant <span class="hlt">calcite</span> cements. Syntaxial overgrowths precipitated on echinoderm grains and contributed to rapid marine lithification of echinoderm-bearing sediments. Bladed, fibrous, and fine-crystalline equant <span class="hlt">calcite</span> cements precipitated in locally suitable sites but their occurrence is limited, and thus played a minor role in marine lithification. Microcrystalline <span class="hlt">calcites</span> also precipitated in lime mud-rich, fine-grained sediments and participated in rapid marine lithification of the Dumugol sediments. The absence of aragonite allochems and cement, and the predominance of <span class="hlt">calcite</span> cement, suggest that the Dumugol sea was undersaturated with respect to aragonite, but supersaturated with respect to <span class="hlt">calcite</span>, which is indicative of a '<span class="hlt">calcite</span> sea'.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014BGeo...11.2295H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014BGeo...11.2295H"><span>Environmental controls on the Emiliania huxleyi <span class="hlt">calcite</span> mass</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Horigome, M. T.; Ziveri, P.; Grelaud, M.; Baumann, K.-H.; Marino, G.; Mortyn, P. G.</p> <p>2014-04-01</p> <p>Although ocean acidification is expected to impact (bio) calcification by decreasing the seawater carbonate ion concentration, [CO32-], there is evidence of nonuniform response of marine calcifying plankton to low seawater [CO32-]. This raises questions about the role of environmental factors other than acidification and about the complex physiological responses behind calcification. Here we investigate the synergistic effect of multiple environmental parameters, including seawater temperature, nutrient (nitrate and phosphate) availability, and carbonate chemistry on the coccolith <span class="hlt">calcite</span> mass of the cosmopolitan coccolithophore Emiliania huxleyi, the most abundant species in the world ocean. We use a suite of surface (late Holocene) sediment samples from the South Atlantic and southwestern Indian Ocean taken from depths lying above the modern lysocline (with the exception of eight samples that are located at or below the lysocline). The coccolith <span class="hlt">calcite</span> mass in our results presents a latitudinal distribution pattern that mimics the main oceanographic features, thereby pointing to the potential importance of seawater nutrient availability (phosphate and nitrate) and carbonate chemistry (pH and pCO2) in determining coccolith mass by affecting primary calcification and/or the geographic distribution of E. huxleyi morphotypes. Our study highlights the importance of evaluating the combined effect of several environmental stressors on calcifying organisms to project their physiological response(s) in a high-CO2 world and improve interpretation of paleorecords.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMPP31B2244C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMPP31B2244C"><span>Sulfate-dependent Anaerobic Oxidation of Methane as a Generation Mechanism for <span class="hlt">Calcite</span> Cap Rock in Gulf Coast Salt Domes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Caesar, K. H.; Kyle, R.; Lyons, T. W.; Loyd, S. J.</p> <p>2015-12-01</p> <p>Gulf Coast salt domes, specifically their <span class="hlt">calcite</span> cap rocks, have been widely recognized for their association with significant reserves of crude oil and natural gas. However, the specific microbial reactions that facilitate the precipitation of these cap rocks are still largely unknown. Insight into the mineralization mechanism(s) can be obtained from the specific geochemical signatures recorded in these structures. Gulf Coast cap rocks contain carbonate and sulfur minerals that exhibit variable carbon (d13C) and sulfur isotope (δ34S) signatures. <span class="hlt">Calcite</span> d13C values are isotopically depleted and show a large range of values from -1 to -52‰, reflecting a mixture of various carbon sources including a substantial methane component. These depleted carbon isotope compositions combined with the presence of abundant sulfide minerals in cap rocks have led to interpretations that invoke microbial sulfate reduction as an important carbonate mineral-yielding process in salt dome environments. Sulfur isotope data from carbonate-associated sulfate (CAS: trace sulfate incorporated within the carbonate mineral <span class="hlt">crystal</span> lattice) provide a more direct proxy for aqueous sulfate in salt dome systems and may provide a means to directly fingerprint ancient sulfate reduction. We find CAS sulfur isotope compositions (δ34SCAS) significantly greater than those of the precursor Jurassic sulfate-salt deposits (which exhibit δ34S values of ~ +15‰). This implies that cap rock carbonate generation occurred via microbial sulfate reduction under closed-system conditions. The co-occurrence of depleted carbonate d13C values (< ~30‰) and the enriched δ34SCAS values are evidence for sulfate-dependent anaerobic oxidation of methane (AOM). AOM, which has been shown to yield extensive seafloor carbonate authigenesis, is also potentially partly responsible for the carbonate minerals of the Gulf Coast <span class="hlt">calcite</span> cap rocks through concomitant production of alkalinity. Collectively, these data shed</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24977921','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24977921"><span>The intrinsically disordered C-RING biomineralization protein, AP7, creates protein phases that introduce nanopatterning and nanoporosities into mineral <span class="hlt">crystals</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chang, Eric P; Russ, Jennie A; Verch, Andreas; Kröger, Roland; Estroff, Lara A; Evans, John Spencer</p> <p>2014-07-15</p> <p>We report an interesting process whereby the formation of nanoparticle assemblies on and nanoporosities within <span class="hlt">calcite</span> <span class="hlt">crystals</span> is directed by an intrinsically disordered C-RING mollusk shell nacre protein, AP7. Under mineralization conditions, AP7 forms protein phases that direct the nucleation of ordered <span class="hlt">calcite</span> nanoparticles via a repetitive protein phase deposition process onto <span class="hlt">calcite</span> <span class="hlt">crystals</span>. These organized nanoparticles are separated by gaps or spaces that become incorporated into the forming bulk <span class="hlt">crystal</span> as nanoporosities. This is an unusual example of organized nanoparticle biosynthesis and mineral modification directed by a C-RING protein phase.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4215888','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4215888"><span>The Intrinsically Disordered C-RING Biomineralization Protein, AP7, Creates Protein Phases That Introduce Nanopatterning and Nanoporosities into Mineral <span class="hlt">Crystals</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p></p> <p>2015-01-01</p> <p>We report an interesting process whereby the formation of nanoparticle assemblies on and nanoporosities within <span class="hlt">calcite</span> <span class="hlt">crystals</span> is directed by an intrinsically disordered C-RING mollusk shell nacre protein, AP7. Under mineralization conditions, AP7 forms protein phases that direct the nucleation of ordered <span class="hlt">calcite</span> nanoparticles via a repetitive protein phase deposition process onto <span class="hlt">calcite</span> <span class="hlt">crystals</span>. These organized nanoparticles are separated by gaps or spaces that become incorporated into the forming bulk <span class="hlt">crystal</span> as nanoporosities. This is an unusual example of organized nanoparticle biosynthesis and mineral modification directed by a C-RING protein phase. PMID:24977921</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3783R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3783R"><span>Interactions of arsenic with <span class="hlt">calcite</span> surfaces revealed by in-situ nanoscale imaging</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Renard, Francois; Putnis, Christine; Montes-Hernandez, German; Ruiz-Agudo, Encarnacion; Hövelmann, Jörn; Sarret, Géraldine</p> <p>2015-04-01</p> <p>Arsenic dissolved in water represents a key environmental and health challenge because several million people are under the threat of contamination. In calcareous environments <span class="hlt">calcite</span> may play an important role in arsenic solubility and transfer in water. Arsenic-<span class="hlt">calcite</span> interactions remain controversial, especially for As(III) which was proposed to be either incorporated as such, or as As(V) after oxidation. Here, we provide the first time-lapse in-situ study of <span class="hlt">calcite</span> dissolution and growth in the presence of solutions with various amounts of As(III) or As(V). This was performed at room temperature and pH range 6-9 using a flow through cell connected to an atomic force microscope (AFM), to study the evolution of the (10-14) <span class="hlt">calcite</span> cleavage surface morphology. Reaction products were then characterized by Raman spectroscopy. In parallel, co-precipitation experiments with either As(III) or As(V) were performed in batch reactors, and the speciation of arsenic in the resulting solids was studied by X-ray absorption spectroscopy (XAS). For As(V), AFM results showed that it interacts strongly with the <span class="hlt">calcite</span> surface, and XAS results showed that As(V) was mostly incorporated in the <span class="hlt">calcite</span> structure. For As(III), AFM results showed much less impact on <span class="hlt">calcite</span> growth and dissolution and less incorporation was observed. This was confirmed by XAS results that indicate that As(III) was partly oxidized into As(V) before being incorporated into <span class="hlt">calcite</span> and the resulting <span class="hlt">calcite</span> contained 36% As(III) and 64% As(V). All these experimental results confirm that As(V) has a much stronger interaction with <span class="hlt">calcite</span> than As(III) and that <span class="hlt">calcite</span> may represent an important reservoir for arsenic in various geological environments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25746637','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25746637"><span>Circular economy in drinking water treatment: reuse of ground pellets as <span class="hlt">seeding</span> material in the pellet softening process.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Schetters, M J A; van der Hoek, J P; Kramer, O J I; Kors, L J; Palmen, L J; Hofs, B; Koppers, H</p> <p>2015-01-01</p> <p>Calcium carbonate pellets are produced as a by-product in the pellet softening process. In the Netherlands, these pellets are applied as a raw material in several industrial and agricultural processes. The sand grain inside the pellet hinders the application in some high-potential market segments such as paper and glass. Substitution of the sand grain with a <span class="hlt">calcite</span> grain (100% calcium carbonate) is in principle possible, and could significantly improve the pellet quality. In this study, the grinding and sieving of pellets, and the subsequent reuse as <span class="hlt">seeding</span> material in pellet softening were tested with two pilot reactors in parallel. In one reactor, garnet sand was used as <span class="hlt">seeding</span> material, in the other ground <span class="hlt">calcite</span>. Garnet sand and ground <span class="hlt">calcite</span> performed equally well. An economic comparison and a life-cycle assessment were made as well. The results show that the reuse of ground <span class="hlt">calcite</span> as <span class="hlt">seeding</span> material in pellet softening is technologically possible, reduces the operational costs by €38,000 (1%) and reduces the environmental impact by 5%. Therefore, at the drinking water facility, Weesperkarspel of Waternet, the transition from garnet sand to ground <span class="hlt">calcite</span> will be made at full scale, based on this pilot plant research.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.2122B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.2122B"><span>Stable carbon isotopes and lipid biomarkers provide new insight into the formation of <span class="hlt">calcite</span> and siderite concretions in organic-matter rich deposits</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Baumann, Lydia; Birgel, Daniel; Wagreich, Michael; Peckmann, Jörn</p> <p>2015-04-01</p> <p>Carbonate concretions from two distinct settings have been studied for their petrography, stable carbon and oxygen isotopes, and lipid biomarker content. Carbonate concretions are in large part products of microbial degradation of organic matter, as for example by sulfate-reducing bacteria, iron-reducing bacteria, and methanogenic archaea. For these prokaryotes certain lipid biomarkers such as hopanoids, terminally-branched fatty acids (bacteria) and isoprenoids (archaea) are characteristic. Two different types of concretions were studied: a) Upper Miocene septarian <span class="hlt">calcite</span> concretions of the southern Vienna Basin embedded in brackish sediments represented by partly bituminous calcareous sands, silts and clays; b) Paleocene-Eocene siderite concretions enclosed in marine, sandy to silty turbidites with varying carbonate contents and marl layers from the Upper Gosau Subgroup in northern Styria. <span class="hlt">Calcite</span> concretions consist of abundant <span class="hlt">calcite</span> microspar (80-90 vol.%), as well as detrital minerals and iron oxyhydroxides. The septarian cracks show beginning cementation with dog-tooth <span class="hlt">calcite</span> to varying degrees. Framboidal pyrite occurs in some of the <span class="hlt">calcite</span> concretions, pointing to bacterial sulfate reduction. Siderite concretions consist of even finer carbonate <span class="hlt">crystals</span>, mainly siderite (40-70 vol.%) but also abundant ferroan <span class="hlt">calcite</span>, accompanied by iron oxyhydroxides and detrital minerals. The δ13C values of the <span class="hlt">calcite</span> concretions (-6.8 to -4.1o ) most likely reflect a combination of bacterial organic matter oxidation and input of marine biodetrital carbonate. The δ18O values range from -8.9 to -7.8o agreeing with a formation within a meteoric environment. The surrounding host sediment shows about 1-2o higher δ13C and δ18O values. The siderite δ13C values (-11.1 to -7.5o ) point to microbial respiration of organic carbon and the δ18O values (-3.5 to +2.2o ) agree with a marine depositional environment. In contrast to the <span class="hlt">calcite</span> concretions, the stable isotope</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DMP.Q1162A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DMP.Q1162A"><span>Highly birefringent <span class="hlt">crystal</span> for Raman transitions with phase modulators</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Arias, Nieves; Abediyeh, Vahide; Hamzeloui, Saeed; Jeronimo-Moreno, Yasser; Gomez, Eduardo</p> <p>2016-05-01</p> <p>We present a system to excite Raman transitions with minimum phase noise. The system uses a phase modulator to generate the phase locked beams required for the transition. We use a long <span class="hlt">calcite</span> <span class="hlt">crystal</span> to filter out one of the sidebands, avoiding the cancellation that appears at high detunings for phase modulation. The measured phase noise is limited by the quality of the microwave synthesizer. We use the <span class="hlt">calcite</span> <span class="hlt">crystal</span> a second time to produce a co-propagating Raman pair with perpendicular polarizations to drive velocity insensitive Raman transitions. Support from CONACYT and Fundacion Marcos Moshinsky.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002EGSGA..27.3649S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002EGSGA..27.3649S"><span>Planktic Foraminiferal Contribution To The Marine <span class="hlt">Calcite</span> Budget</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schiebel, R.</p> <p></p> <p>The vertical flux and sedimentation of planktic foraminiferal tests is quantified and a global planktic foraminiferal CaCO3 budget is presented. The eastern North Atlantic, the Arabian Sea, and the Caribbean were identified as key areas for this investiga- tion, covering a wide spectrum of ecological conditions and faunal compositions. Test and <span class="hlt">calcite</span> flux rates are calculated according to the distribution of species obtained from multinet and sediment trap samples. Population dynamics of modern plank- tic foraminifers are discussed as a prerequesite for the quantification of the <span class="hlt">calcite</span> budget, highlighting the importance of ecological, autecological (e.g., reproduction), and biogeochemical conditions that determine the presence or absence of species. To complete the open-marine, particulate CaCO3 inventory, the contribution of coccol- ithophores, pteropods, and calcareous dinophytes is discussed. It is assumed that the global planktic foraminiferal <span class="hlt">calcite</span> flux at 100 m depth amounts to 1.3-3.2 Gigatons per year, equivalent to 23-56% of the total open marine CaCO3 flux. The preservation of tests varies on a regional and temporal scale, and is affected by local hydrogra- phy and dissolution susceptibility of planktic foraminiferal tests. Throughout most of the year (off-peak periods) a major portion of tests is dissolved above 700 m water depth while individually settling through the water column, with on average only 1- 3% of the initially exported CaCO3 reaching the deep sea floor. Pulsed flux events, mass dumps of fast settling particles, yield a major contribution of the tests to the formation of deep-sea sediments. On an annual average, about one fourth of the ini- tially produced planktic foraminiferal test CaCO3 may settle on the sea floor. The total planktic foraminiferal contribution of CaCO3 to global deep-marine surface sediments amounts to 0.36-0.88 Gt per year, which is 32-80% of the total CaCO3 budget that is estimated at 1.1 Gt per year (e</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/953817','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/953817"><span>In situ study of the R{bar 3}c-R{bar 3}m orientational disorder in <span class="hlt">calcite</span>.</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Antao, S. M.; Hassan, I.; Mulder, W. H.; Lee, P. L.; Toby, B. H.; X-Ray Science Division; Univ. of West Indies</p> <p>2009-01-01</p> <p>The temperature dependences of the <span class="hlt">crystal</span> structure and intensities of the (113) and (211) reflections in <span class="hlt">calcite</span>, CaCO{sub 3}, were studied using Rietveld structure refinements based on synchrotron powder X-ray diffraction data. <span class="hlt">Calcite</span> transforms from R{bar 3}c to R{bar 3}m at about T{sub c} = 1240 K. A CO{sub 3} group occupies, statistically, two positions with equal frequency in the disordered R{bar 3}m phase, but with unequal frequency in the partially ordered R{bar 3}c phase. One position for the CO{sub 3} group is rotated by 180{sup o} with respect to the other. The unequal occupancy of the two orientations in the partially ordered R{bar 3}c phase is obtained directly from the occupancy factor, x, for the O1 site and gives rise to the order parameter, S = 2x - 1. The a cell parameter shows a negative thermal expansion at low T, followed by a plateau region at higher T, then a steeper contraction towards T{sub c}, where the CO{sub 3} groups disorder in a rapid process. Using a modified Bragg-Williams model, fits were obtained for the order parameter S, and for the intensities of the (113) and (211) reflections.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NIMPB.383...93K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NIMPB.383...93K"><span>X-ray dose response of <span class="hlt">calcite</span>-A comprehensive analysis for optimal application in TL dosimetry</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kalita, J. M.; Wary, G.</p> <p>2016-09-01</p> <p>The effect of various annealing treatments on dosimetric characteristics of orange <span class="hlt">calcite</span> (CaCO3) mineral has been studied in detail. Quantitative analysis on the dose response shows that the 573 K annealed sample showed sublinear dose response from 10 mGy to 1 Gy. The fading and reproducibility of this sample are also good enough for dosimetric application. However, a specific annealing treatment after irradiation shows some significant improvements in the dosimetric characteristics of the sample. The 773 K pre-annealed sample, after X-ray irradiation post-annealing at 340 K for 6 min provides linear dose response from 10 mGy to 3.60 Gy, very less fading and good reproducibility. Moreover, this sample after post-annealing at 380 K for 6 min shows linear dose response from 10 mGy to 5.40 Gy when analyzed from the ∼408 K thermoluminescence (TL) glow peak. Analysis of TL glow curves confirmed that the 1.30 eV trap center in <span class="hlt">calcite</span> <span class="hlt">crystal</span> is the most effective trapping site for dosimetric application.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=industrial+AND+engineering+AND+chemistry&pg=5&id=EJ343011','ERIC'); return false;" href="http://eric.ed.gov/?q=industrial+AND+engineering+AND+chemistry&pg=5&id=EJ343011"><span>Project <span class="hlt">SEED</span>.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Chemical and Engineering News, 1986</p> <p>1986-01-01</p> <p>Reports on Project <span class="hlt">SEED</span> (Summer Educational Experience for the Disadvantaged) a project in which high school students from low-income families work in summer jobs in a variety of academic, industrial, and government research labs. The program introduces the students to career possibilities in chemistry and to the advantages of higher education.…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/10964705','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/10964705"><span><span class="hlt">Crystal</span> structures of the ribonuclease MC1 from bitter gourd <span class="hlt">seeds</span>, complexed with 2'-UMP or 3'-UMP, reveal structural basis for uridine specificity.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Suzuki, A; Yao, M; Tanaka, I; Numata, T; Kikukawa, S; Yamasaki, N; Kimura, M</p> <p>2000-08-28</p> <p>Ribonuclease MC1 (RNase MC1) isolated from <span class="hlt">seeds</span> of bitter gourd (Momordica charantia) consists of 190 amino acids and is characterized by a preferential cleavage at the 5'-side of uridine. This uridine specificity distinguishes RNase MC1 from other enzymes belonging to the RNase T2 family. The three-dimensional structures of RNase MC1, in a complex with either 2'-UMP or 3'-UMP, were determined at 1.48 and 1.77 A resolutions, respectively. The side chains of Gln9 and Asn71 interact with O4 and N3, respectively, of the uracil base by hydrogen bondings. In addition, the uracil base is sandwiched by the hydrophobic side chains of Leu73 and Phe80. Compared with these amino acid residues and corresponding residues in RNases in the RNase T2 family, Gln9 and Phe80 are highly conserved in the RNases in T2 family, while Asn71 and Leu73 in RNase MC1 are variant in sequences. It is thus likely that interactions of the side chains of Asn71 and Leu73 with the uracil base are responsible for the absolute uridine specificity of RNase MC1. Site-directed mutagenesis experiments showed that replacement of Asn by Thr decreased both the catalytic efficiency and the binding affinity by 2.3- and 7.0-fold, respectively, and substitution of Leu73 for Ala predominantly decreased the binding affinity by 14. 5-fold, compared with findings in case of wild-type RNase MC1. It is thus demonstrated that Asn71 and Leu73 play an essential role in uridine preference for RNase MC1.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6121236','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6121236"><span>Isotopic composition of a <span class="hlt">calcite</span>-cemented layer in the Lower Jurassic Bridport Sands, southern England: Implications for formation of laterally extensive <span class="hlt">calcite</span>-cemented layers</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bjoerkum, P.A. ); Walderhaug, O. )</p> <p>1993-07-01</p> <p>[delta][sup 18]O[sub PDB] and [delta][sup 13]C[sub PDB] values have been measured on 107 <span class="hlt">calcite</span> cement samples from a laterally extensive (> 3 km) and continuous <span class="hlt">calcite</span>-cemented layer 0.5 m thick in the coastal exposures of the Lower Jurassic shallow-marine Bridport Sands in Dorset, southern England. The samples were taken from a two-dimensional grid with 10-cm horizontal and vertical spacing between samples and along individual vertical lines across the <span class="hlt">calcite</span>-cemented layer, [delta][sup 18]O[sub PDB] values vary between [minus]4.8% and [minus]9.2% and decrease radially outwards from points with lateral spacings on the order of 0.5-1 m in the middle of the <span class="hlt">calcite</span>-cemented layer. The [delta][sup 18]O[sub PDB] values therefore indicate that the <span class="hlt">calcite</span>-cemented layer was formed by merging of concretions. All [delta][sup 13]C[sub PDB] values measured are in the narrow range [minus]2.2% to [minus]0.5%, which suggests that the dominant source of <span class="hlt">calcite</span> cement in the layer was biogenic carbonate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/6458514','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/6458514"><span>Carbon and oxygen isotopes in apatite CO/sub 2/ and co-existing <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kolodny, Y.; Kaplan, I. R.</p> <p>1981-04-01</p> <p>Carbon and oxygen isotopes were analyzed in carbonate apatite CO/sub 2/ and in co-existing <span class="hlt">calcite</span>. Both C and O in apatite CO/sub 2/ are enriched in the respective light isotopes relative to <span class="hlt">calcite</span>. These results confirm the proposition that carbonate is part of the apatite structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4759641','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4759641"><span><span class="hlt">Calcite</span> orientations and composition ranges within teeth across Echinoidea</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Stock, Stuart R.; Ignatiev, Konstantin; Lee, Peter L.; Almer, Jonathan D.</p> <p>2016-01-01</p> <p>Sea urchin’s teeth from four families of order Echinoida and from orders Temnopleuroida, Arbacioida and Cidaroida were studied with synchrotron x-ray diffraction. The high and very high Mg <span class="hlt">calcite</span> phases of the teeth, i.e. the first and second stage mineral constituents, respectively, have the same crystallographic orientations. The co-orientation of first and second stage mineral, which the authors attribute to epitaxy, extends across the phylogenic width of the extant regular sea urchins and demonstrates that this is a primitive character of this group. The range of compositions Δx for the two phases of Ca1−xMgxCO3 is about 0.20 or greater and is consistent with a common biomineralization process. PMID:25158180</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMPP22B..02B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMPP22B..02B"><span>A global deglacial negative carbon isotope excursion in speleothem <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Breecker, D.</p> <p>2015-12-01</p> <p>δ13C values of speleothem <span class="hlt">calcite</span> decreased globally during the last deglaciation defining a carbon isotope excursion (CIE) despite relatively constant δ13C values of carbon in the ocean-atmosphere system. The magnitude of the CIE varied with latitude, increasing poleward from ~2‰ in the tropics to as much as 7‰ at high latitudes. This recent CIE provides an interesting comparison with CIEs observed in deep time. A substantial portion of this CIE can be explained by the increase in atmospheric pCO2 that accompanied deglaciation. The dependence of C3 plant δ13C values on atmospheric pCO2 predicts a 2‰ δ13C decrease driven by the deglacial pCO2 increase. I propose that this signal was transferred to caves and thus explains nearly 100% of the CIE magnitude observed in the tropics and no less than 30% at the highest latitudes in the compilation. An atmospheric pCO2 control on speleothem δ13C values, if real, will need to be corrected for using ice core data before δ13C records can be interpreted in a paleoclimate context. The decrease in the magnitude of the equilibrium <span class="hlt">calcite</span>-CO2 carbon isotope fractionation factor explains a maximum of 1‰ of the CIE at the highest northern latitude in the compilation, which experienced the largest deglacial warming. Much of the residual extratropical CIE was likely driven by increasing belowground respiration rates, which were presumably pronounced at high latitudes as glacial retreat exposed fresh surfaces and/or vegetation density increased. The largest increases in belowground respiration would have therefore occurred at the highest latitudes, explaining the meridional trend. This work supports the notion that increases in atmospheric pCO2 and belowground respiration rates can result in large CIEs recorded in terrestrial carbonates, which, as previously suggested, may explain the magnitude of the PETM CIE as recorded by paleosol carbonates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/tei/0118/report.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/tei/0118/report.pdf"><span>The quantitative determination of <span class="hlt">calcite</span> associated with the carbonate-bearing apatites</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Silverman, Sol R.; Fuyat, Ruth K.; Weiser, Jeanne D.</p> <p>1951-01-01</p> <p>The CO2 combined as <span class="hlt">calcite</span> in carbonate-bearing apatites as been distinguished from that combined as carbonate-apatite, or present in some form other than <span class="hlt">calcite</span>, by use of X-ray powder patterns, differential thermal analyses, and differential solubility tests. These methods were applied to several pure apatite minerals, to one fossil bone, and to a group of phosphorites from the Phosphoria formation of Permian age from Trail Canyon and the Conda mine, Idaho, and the Laketown district, Utah. With the exceptions of pure fluorapatite, pure carbonate-flueorapatite, and one phosphorite from Trail Canyon, these substances contain varying amounts of <span class="hlt">calcite</span>, but in all the samples an appreciable part of the carbonite content is not present as <span class="hlt">calcite</span>. The results of solubility tests, in which the particle size of sample and the length of solution time were varied, imply that the carbonate content is not due to shielded <span class="hlt">calcite</span> entrapped along an internal network of surfaces.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1130649','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1130649"><span>Influence of <span class="hlt">calcite</span> on uranium(VI) reactive transport in the groundwater–river mixing zone</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ma, Rui; Liu, Chongxuan; Greskowiak, Janek; Prommer, Henning; Zachara, John M.; Zheng, Chunmiao</p> <p>2014-01-23</p> <p><span class="hlt">Calcite</span> is an important mineral that can affect uranyl reactive transport in subsurface sediments. This study investigated the distribution of <span class="hlt">calcite</span> and its influence on uranyl adsorption and reactive transport in the groundwater-river mixing zone at US Hanford 300A, Washington State. Simulations using a 2D reactive transport model under field-relevant hydrogeochemical conditions revealed a complex distribution of <span class="hlt">calcite</span> concentration as a result of dynamic groundwater-river interactions. The <span class="hlt">calcite</span> concentration distribution in turn affected the spatial and temporal changes in aqueous carbonate, calcium, and pH, which subsequently influenced U(VI) mobility and discharge rates into the river. The results implied that <span class="hlt">calcite</span> distribution and its concentration dynamics is an important consideration for field characterization, monitoring, and reactive transport prediction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24188740','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24188740"><span>Unusual micrometric <span class="hlt">calcite</span>-aragonite interface in the abalone shell Haliotis (Mollusca, Gastropoda).</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Dauphin, Yannicke; Cuif, Jean-Pierre; Castillo-Michel, Hiram; Chevallard, Corinne; Farre, Bastien; Meibom, Anders</p> <p>2014-02-01</p> <p>Species of Haliotis (abalone) show high variety in structure and mineralogy of the shell. One of the European species (Haliotis tuberculata) in particular has an unusual shell structure in which <span class="hlt">calcite</span> and aragonite coexist at a microscale with small patches of aragonite embedded in larger <span class="hlt">calcitic</span> zones. A detailed examination of the boundary between <span class="hlt">calcite</span> and aragonite using analytical microscopies shows that the organic contents of <span class="hlt">calcite</span> and aragonite differ. Moreover, changes in the chemical composition of the two minerals seem to be gradual and define a micrometric zone of transition between the two main layers. A similar transition zone has been observed between the layers in more classical and regularly structured mollusk shells. The imbrication of microscopic patches of aragonite within a <span class="hlt">calcitic</span> zone suggests the occurrence of very fast physiological changes in these taxa.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JMMM..416..384F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JMMM..416..384F"><span>Growth of single <span class="hlt">crystals</span> of BaFe12O19 by solid state <span class="hlt">crystal</span> growth</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fisher, John G.; Sun, Hengyang; Kook, Young-Geun; Kim, Joon-Seong; Le, Phan Gia</p> <p>2016-10-01</p> <p>Single <span class="hlt">crystals</span> of BaFe12O19 are grown for the first time by solid state <span class="hlt">crystal</span> growth. <span class="hlt">Seed</span> <span class="hlt">crystals</span> of BaFe12O19 are buried in BaFe12O19+1 wt% BaCO3 powder, which are then pressed into pellets containing the <span class="hlt">seed</span> <span class="hlt">crystals</span>. During sintering, single <span class="hlt">crystals</span> of BaFe12O19 up to ∼130 μm thick in the c-axis direction grow on the <span class="hlt">seed</span> <span class="hlt">crystals</span> by consuming grains from the surrounding polycrystalline matrix. Scanning electron microscopy-energy dispersive spectroscopy analysis shows that the single <span class="hlt">crystal</span> and the surrounding polycrystalline matrix have the same chemical composition. Micro-Raman scattering shows the single <span class="hlt">crystal</span> to have the BaFe12O19 structure. The optimum growth temperature is found to be 1200 °C. The single <span class="hlt">crystal</span> growth behavior is explained using the mixed control theory of grain growth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013MeScT..24h5203M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013MeScT..24h5203M"><span>SOA-based fiber ring laser with <span class="hlt">seed</span> of DFB wavelength scanning for relative humidity measurement using an air-guided photonic <span class="hlt">crystal</span> fiber</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mohd Noor, M. Y.; Khalili, N.; Peng, G. D.</p> <p>2013-08-01</p> <p>We propose a novel ring laser for non-hygroscopic coating relative humidity (RH) fiber sensor by means of infrared absorption spectroscopy. A semiconductor optical amplifier (SOA)-based fiber ring laser is used in this scheme. No tunable optical filter is required for the ring laser scheme as wavelength scanning is introduced in the ring using a distributed feedback (DFB) laser. An air-guided photonic <span class="hlt">crystal</span> fiber (AGPCF) is included in the ring cavity that acts as a sensing head. The detection of gas humidity inside the air holes of AGPCF is determined by DFB wavelength scanning around 1368.59 nm water vapor absorption peak with SOA as a gain medium in the ring. We have experimentally implemented the wavelength scanning of SOA-based fiber ring laser scheme with an AGPCF sensing head of 5 cm and a small gap between single mode fiber and AGPCF to allow air diffusion in and out of the air holes inside the AGPCF. The sensitivity of the sensor is increased from 2.47 to 10.93 mV/1% RH over the range from 0 to 90% RH when the non-lasing mode (single-pass absorption spectroscopy) of the sensor is changed into the lasing mode (multi-pass absorption spectroscopy).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeCoA.159...61R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeCoA.159...61R"><span>Interactions of arsenic with <span class="hlt">calcite</span> surfaces revealed by in situ nanoscale imaging</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Renard, François; Putnis, Christine V.; Montes-Hernandez, German; Ruiz-Agudo, Encarnacion; Hovelmann, Jörn; Sarret, Géraldine</p> <p>2015-06-01</p> <p>Arsenic dissolved in water represents a key environmental and health challenge because several million people are under the threat of contamination. In calcareous environments <span class="hlt">calcite</span> may play an important role in arsenic solubility and transfer in water. Arsenic-<span class="hlt">calcite</span> interactions remain controversial, especially for As(III) which was proposed to be either incorporated as such, or as As(V) after oxidation. Here, we provide the first time-lapse in situ study of the evolution of the (10-14) <span class="hlt">calcite</span> cleavage surface morphology during dissolution and growth in the presence of solutions with various amounts of As(III) or As(V) at room temperature and pH range 6-11 using a flow-through cell connected to an atomic force microscope (AFM). Reaction products were then characterized by Raman spectroscopy. In parallel, co-precipitation experiments with either As(III) or As(V) were performed in batch reactors, and the speciation of arsenic in the resulting solids was studied by X-ray absorption spectroscopy (XAS). For As(V), AFM results showed that it interacts strongly with the <span class="hlt">calcite</span> surface, and XAS results showed that As(V) was mostly incorporated in the <span class="hlt">calcite</span> structure. For As(III), AFM results showed much less impact on <span class="hlt">calcite</span> growth and dissolution and less incorporation was observed. This was confirmed by XAS results that indicate that As(III) was partly oxidized into As(V) before being incorporated into <span class="hlt">calcite</span> and the resulting <span class="hlt">calcite</span> contained 36% As(III) and 64% As(V). All these experimental results confirm that As(V) has a much stronger interaction with <span class="hlt">calcite</span> than As(III) and that <span class="hlt">calcite</span> may represent an important reservoir for arsenic in various geological environments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/20006591','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/20006591"><span>Diel cycles in <span class="hlt">calcite</span> production and dissolution in a eutrophic basin</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Cicerone, D.S.; Stewart, A.J.; Roh, Y.</p> <p>1999-10-01</p> <p><span class="hlt">Calcite</span> production is understood largely as a longer-term phenomenon (e.g., seasonal whitings) that can occur in hardwater lakes, and is significant ecologically because it can slow the rate of eutrophication by reducing, through adsorption, the availability of nutrients to primary producers. In this study the authors show that rapid changes in concentration of dissolved CO{sub 2} by photosynthesis and respiration within a eutrophic basin generated strong day-to-night cycles in <span class="hlt">calcite</span> production and dissolution. Diel cycles in <span class="hlt">calcite</span> production and dissolution were large enough that they could drive secondary diel cycles in the availability of metals that strongly sorb to the surfaces of <span class="hlt">calcite</span> particles. They explored the possibility of the secondary diel cycling of metals by intensive 7-d in situ monitoring of water-quality conditions in a shallow, eutrophic spill-control basin near an industrial facility in eastern Tennessee; inspecting data from a 7-year record of water-quality parameters for this basin; analyzing physicochemical characteristics and mineralogic composition of sediments in the basin; and conducting laboratory experiments to characterize the interaction of <span class="hlt">calcite</span> with Cd, under solid-liquid nonequilibrium conditions. The authors found that the basin accumulated and stored <span class="hlt">calcite</span>. In situ monitoring showed that <span class="hlt">calcite</span> was produced during daylight, and tended to dissolve again at night; the <span class="hlt">calcite</span> production and dissolution processes seemed to be modulated by dissolved-phase CO{sub 2} dynamics, in concert with large diel fluctuations in pCa, pH, and Po{sub 2}. Laboratory experiments showed a rapid interaction ({lt}6 h) of Cd with <span class="hlt">calcite</span>, in response to dissolved CO{sub 2} changes. Thus, concentrations of dissolved Cd can vary over daily cycles, mediated by diel changes in <span class="hlt">calcite</span> production and dissolution. Thermodynamic considerations suggest that other metals, such as Zn, Sr, Ni, and Ba, may demonstrate this behavior as well.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006Geo....34..525R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006Geo....34..525R"><span>Scleractinian corals produce <span class="hlt">calcite</span>, and grow more slowly, in artificial Cretaceous seawater</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ries, Justin B.; Stanley, Steven M.; Hardie, Lawrence A.</p> <p>2006-07-01</p> <p>The mineralogies of most biotic and abiotic carbonates have alternated in synchroneity between the <span class="hlt">calcite</span> (hexagonal) and aragonite (orthorhombic) polymorphs of CaCO3 throughout the Phanerozoic Eon. These intervals of <span class="hlt">calcite</span> and aragonite production, or <span class="hlt">calcite</span> seas and aragonite seas, are thought to be caused primarily by secular variation in the molar magnesium/calcium ratio of seawater (m</em>Mg/Ca > 2 = aragonite + high-Mg <span class="hlt">calcite</span>; m</em>Mg/Ca < 2 = low-Mg <span class="hlt">calcite</span>), a ratio that has oscillated between 1.0 and 5.2 throughout the Phanerozoic. In laboratory experiments, we show that three species of scleractinian corals, which produce aragonite in modern seawater and which have flourished as important reef builders primarily during aragonite seas of the past, began producing <span class="hlt">calcite</span> in artificial seawater with an ambient m</em>Mg/Ca ratio below that of modern seawater (5.2). The corals produced progressively higher percentages of <span class="hlt">calcite</span> and calcified at lower rates with further reduction of the ambient m</em>Mg/Ca ratio. In artificial seawater of imputed Late Cretaceous composition (m</em>Mg/Ca = 1.0), which favors the precipitation of the <span class="hlt">calcite</span> polymorph, scleractinian corals produced skeletons containing >30% low-Mg <span class="hlt">calcite</span> (skeletal m</em>Mg/Ca < 0.04). These results indicate that the skeletal mineral used by scleractinian corals is partially determined by seawater chemistry. Furthermore, slow calcification rates, resulting from the production of largely aragonitic skeletons in chemically unfavorable seawater (m</em>Mg/Ca < 2), probably contributed to the scleractinians' diminished reef-building role in the <span class="hlt">calcite</span> seas of Late Cretaceous and early Cenozoic time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JSG....70..200K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JSG....70..200K"><span>The mechanical and microstructural behaviour of <span class="hlt">calcite</span>-dolomite composites: An experimental investigation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kushnir, Alexandra R. L.; Kennedy, L. A.; Misra, Santanu; Benson, Philip; White, J. C.</p> <p>2015-01-01</p> <p>The styles and mechanisms of deformation associated with many variably dolomitized limestone shear systems are strongly controlled by strain partitioning between dolomite and <span class="hlt">calcite</span>. Here, we present experimental results from the deformation of four composite materials designed to address the role of dolomite on the strength of limestone. Composites were synthesized by hot isostatic pressing mixtures of dolomite (Dm) and <span class="hlt">calcite</span> powders (% Dm: 25%-Dm, 35%-Dm, 51%-Dm, and 75%-Dm). In all composites, <span class="hlt">calcite</span> is finer grained than dolomite. The synthesized materials were deformed in torsion at constant strain rate (3 × 10-4 and 1 × 10-4 s-1), high effective pressure (262 MPa), and high temperature (750 °C) to variable finite shear strains. Mechanical data show an increase in yield strength with increasing dolomite content. Composites with <75% dolomite (the remaining being <span class="hlt">calcite</span>), accommodate significant shear strain at much lower shear stresses than pure dolomite but have significantly higher yield strengths than anticipated for 100% <span class="hlt">calcite</span>. The microstructure of the fine-grained <span class="hlt">calcite</span> suggests grain boundary sliding, accommodated by diffusion creep and dislocation glide. At low dolomite concentrations (i.e. 25%), the presence of coarse-grained dolomite in a micritic <span class="hlt">calcite</span> matrix has a profound effect on the strength of composite materials as dolomite grains inhibit the superplastic flow of <span class="hlt">calcite</span> aggregates. In high (>50%) dolomite content samples, the addition of 25% fine-grained <span class="hlt">calcite</span> significantly weakens dolomite, such that strain can be partially localized along narrow ribbons of fine-grained <span class="hlt">calcite</span>. Deformation of dolomite grains by shear fracture is observed; there is no intracrystalline deformation in dolomite irrespective of its relative abundance and finite shear strain.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1065525','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1065525"><span>Transformation and <span class="hlt">Crystallization</span> Energetics of Synthetic and Biogenic Amorphous Calcium Carbonate</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Radha, A. V.; Forbes, Tori Z.; Killian, Christopher E.; Gilbert, P.U.P.A; Navrotsky, Alexandra</p> <p>2010-01-01</p> <p>Amorphous calcium carbonate (ACC) is a metastable phase often observed during low temperature inorganic synthesis and biomineralization. ACC transforms with aging or heating into a less hydrated form, and with time <span class="hlt">crystallizes</span> to <span class="hlt">calcite</span> or aragonite. The energetics of transformation and <span class="hlt">crystallization</span> of synthetic and biogenic (extracted from California purple sea urchin larval spicules, Strongylocentrotus purpuratus) ACC were studied using isothermal acid solution calorimetry and differential scanning calorimetry. Transformation and <span class="hlt">crystallization</span> of ACC can follow an energetically downhill sequence: more metastable hydrated ACC → less metastable hydrated ACC→anhydrous ACC ~ biogenic anhydrous ACC→vaterite → aragonite → <span class="hlt">calcite</span>. In a given reaction sequence, not all these phases need to occur. The transformations involve a series of ordering, dehydration, and <span class="hlt">crystallization</span> processes, each lowering the enthalpy (and free energy) of the system, with <span class="hlt">crystallization</span> of the dehydrated amorphous material lowering the enthalpy the most. ACC is much more metastable with respect to <span class="hlt">calcite</span> than the crystalline polymorphs vaterite or aragonite. The anhydrous ACC is less metastable than the hydrated, implying that the structural reorganization during dehydration is exothermic and irreversible. Dehydrated synthetic and anhydrous biogenic ACC are similar in enthalpy. The transformation sequence observed in biomineralization could be mainly energetically driven; the first phase deposited is hydrated ACC, which then converts to anhydrous ACC, and finally <span class="hlt">crystallizes</span> to <span class="hlt">calcite</span>. The initial formation of ACC may be a first step in the precipitation of <span class="hlt">calcite</span> under a wide variety of conditions, including geological CO₂ sequestration.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GeCoA.114..188M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GeCoA.114..188M"><span>Kinetics of Mg partition and Mg stable isotope fractionation during its incorporation in <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mavromatis, Vasileios; Gautier, Quentin; Bosc, Olivier; Schott, Jacques</p> <p>2013-08-01</p> <p><span class="hlt">Calcite</span> growth experiments have been performed in the presence of aqueous Mg at 25 °C and 1 bar pCO2 to quantify magnesium partition coefficient D={(Mg/Ca)}/{(Mg/Ca)} and Mg isotope fractionation between <span class="hlt">calcite</span> and reactive fluid (Δ26Mgcalcite-fluid) as a function of <span class="hlt">calcite</span> precipitation rate rp (mol m-2 s-1). Mg partition coefficient, DMg, increases with <span class="hlt">calcite</span> growth rate according to: LogD=0.2517(±0.0150)×Logrp+0.0944(±0.0182); R2=0.93,(10-8.3⩽rp⩽10-6.6molms) Δ26Mgcalcite-fluid was found to depend heavily on <span class="hlt">calcite</span> growth rate with preferential incorporation of 24Mg in <span class="hlt">calcite</span> and the extent of isotope fractionation decreasing with increasing <span class="hlt">calcite</span> growth rate in accord with: Δ26Mg=0.7918(±0.0452)×Logrp+3.2366(±0.3360); R2=0.97(10-8.3⩽rp⩽10-6.6molms) The negative Δ26Mgcalcite-fluid values found in this study, with <span class="hlt">calcite</span> overgrowths enriched in light Mg, are consistent with (i) recent experimental data on Mg isotope fractionation during low-Mg <span class="hlt">calcite</span> homogeneous precipitation (Immenhauser et al., 2010) and magnesite growth (Pearce et al., 2012) and (ii) with theoretical values calculated for Mg-<span class="hlt">calcite</span> by density-functional electronic structure models (Rustad et al., 2010). The deviation of the isotopic composition of precipitated Mg-<span class="hlt">calcite</span> from the equilibrium mass fractionation line in a three isotope diagram is a linear function of <span class="hlt">calcite</span> growth rate. The equilibrium Δ26Mgcalcite-fluid value at 25 °C derived from this linear extrapolation, Δ26Mgcalcite-fluid = -3.5 ± 0.2‰ (2σ), is in good agreement with the theoretical value calculated by Rustad et al. (2010) for Mg-<span class="hlt">calcite</span> (Δ26Mgcalcite-fluid = -3.6‰; BP86 functional). A striking feature of the results of this study is the decrease of the extent of Mg isotope fractionation (from -3.16‰ to -1.88‰) with the increase of <span class="hlt">calcite</span> precipitation rate (from 10-8.3 to 10-6.6 mol m-2 s-1) which is opposite to the variation of Ca, Ba and Sr isotope fractionation with <span class="hlt">calcite</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1991GeCoA..55.1991C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1991GeCoA..55.1991C"><span>δ 18O values, 87Sr /86Sr and Sr/Mg ratios of Late Devonian abiotic marine <span class="hlt">calcite</span>: Implications for the composition of ancient seawater</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Carpenter, Scott J.; Lohmann, K. C.; Holden, Peter; Walter, Lynn M.; Huston, Ted J.; Halliday, Alex N.</p> <p>1991-07-01</p> <p>Late Devonian (Frasnian) abiotic marine <span class="hlt">calcite</span> has been microsampled and analyzed for 87Sr /86Sr ratios, δ 18O and δ 13C values, and minor element concentrations. Portions of marine cement <span class="hlt">crystals</span> from the Alberta and Canning Basins have escaped diagenetic alteration and preserve original marine δ 18O values (-4.8%. ± 0.5, PDB), δ 13C values (+2.0 to +3.0%., PDB), 87Sr /86Sr ratios (0.70805 ± 3), and Sr/Mg weight ratios (0.04 to 0.05). Marine 87Sr /86Sr ratios are globally consistent and can be correlated within the Alberta Basin, and among the Alberta, Canning, and Williston Basins. Correlation of isotopic and chemical data strengthen the conclusion that marine cements from the Leduc Formation preserve original marine δ 18O values which are 3 to 4%. lower than those of modern marine cements. These low δ 18O values are best explained by precipitation from 18O-depleted seawater and not by elevated seawater temperature or diagenetic alteration. For comparison with Devonian data, analogous data were collected from Holocene Mg-<span class="hlt">calcite</span> and aragonite marine cements from Enewetak Atoll, Marshall Islands. Mg-<span class="hlt">calcite</span> and aragonite marine cements are in isotopic equilibrium with ambient seawater, and Mg-<span class="hlt">calcite</span> cements are homogeneous with respect to Sr and Mg contents. Empirically derived homogeneous distribution coefficients for Mg and Sr in modern, abiotic Mg-<span class="hlt">calcite</span> from Enewetak Atoll are 0.034 and 0.15, respectively. An equation describing the dependence of DSr on Mg content was based on a compilation of Sr and Mg data from Holocene abiotic marine <span class="hlt">calcite</span> ( DSr = 3.52 × 10 -6 (ppm Mg) + 6.20 × 10 -3). Unlike that derived from experimental data, this Sr-Mg relation is consistent over a range of 4 to 20 mol% MgCO 3 and may represent precipitation phenomena which are minimally controlled by kinetic effects. Comparison of Sr and Mg contents of analogous Devonian and Holocene marine cements suggests that the Mg/Ca ratio of Late Devonian seawater was</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/860281','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/860281"><span>STRONTIUM ISOTOPE EVOLUTION OF PORE WATER AND <span class="hlt">CALCITE</span> IN THE TOPOPAH SPRING TUFF, YUCCA MOUNTAIN , NEVADA</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>B.D. Marshall; K. Futa</p> <p>2001-02-07</p> <p>Yucca Mountain, a ridge of Miocene volcanic rocks in southwest Nevada, is being characterized as a site for a potential high-level radioactive waste repository. One issue of concern for the future performance of the potential repository is the movement of water in and around the potential repository horizon. Past water movement in this unsaturated zone is indicated by fluid inclusions trapped in <span class="hlt">calcite</span> coatings on fracture footwall surfaces and in some lithophysal cavities. Some of the fluid inclusions have homogenization temperatures above the present-day geotherm (J.F. Whelan, written communication), so determining the ages of the <span class="hlt">calcite</span> associated with those fluid inclusions is important in understanding the thermal history of the potential repository site. <span class="hlt">Calcite</span> ages have been constrained by uranium-lead dating of silica polymorphs (opal and chalcedony) that are present in most coatings. The opal and chalcedony ages indicate that deposition of the <span class="hlt">calcite</span> and opal coatings in the welded part of the Topopah Spring Tuff (TSw hydrogeologic unit) spanned nearly the entire history of the 12.8-million-year-old rock mass at fairly uniform overall long-term rates of deposition (within a factor of five). Constraining the age of a layer of <span class="hlt">calcite</span> associated with specific fluid inclusions is complicated. <span class="hlt">Calcite</span> is commonly bladed with complex textural relations, and datable opal or chalcedony may be millions of years older or younger than the <span class="hlt">calcite</span> layer or may be absent from the coating entirely. Therefore, a more direct method of dating the <span class="hlt">calcite</span> is presented in this paper by developing a model for strontium evolution in pore water in the TSw as recorded by the strontium coprecipitated with calcium in the <span class="hlt">calcite</span>. Although the water that precipitated the <span class="hlt">calcite</span> in fractures and cavities may not have been in local isotopic equilibrium with the pore water, the strontium isotope composition of all water in the TSw is primarily controlled by water</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4030687','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4030687"><span><span class="hlt">Crystallization</span> of Macromolecules</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Friedmann, David; Messick, Troy; Marmorstein, Ronen</p> <p>2014-01-01</p> <p>X-ray crystallography has evolved into a very powerful tool to determine the three-dimensional structure of macromolecules and macromolecular complexes. The major bottleneck in structure determination by X-ray crystallography is the preparation of suitable crystalline samples. This unit outlines steps for the <span class="hlt">crystallization</span> of a macromolecule, starting with a purified, homogeneous sample. The first protocols describe preparation of the macromolecular sample (i.e., proteins, nucleic acids, and macromolecular complexes). The preparation and assessment of <span class="hlt">crystallization</span> trials is then described, along with a protocol for confirming whether the <span class="hlt">crystals</span> obtained are composed of macromolecule as opposed to a <span class="hlt">crystallization</span> reagent. Next, the optimization of <span class="hlt">crystallization</span> conditions is presented. Finally, protocols that facilitate the growth of larger <span class="hlt">crystals</span> through <span class="hlt">seeding</span> are described. PMID:18429252</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4128474','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4128474"><span><span class="hlt">Crystallization</span> of Macromolecules</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Friedmann, David; Messick, Troy; Marmorstein, Ronen</p> <p>2014-01-01</p> <p>X-ray crystallography has evolved into a very powerful tool to determine the three-dimensional structure of macromolecules and macromolecular complexes. The major bottleneck in structure determination by X-ray crystallography is the preparation of suitable crystalline samples. This unit outlines steps for the <span class="hlt">crystallization</span> of a macromolecule, starting with a purified, homogeneous sample. The first protocols describe preparation of the macromolecular sample (i.e., proteins, nucleic acids, and macromolecular complexes). The preparation and assessment of <span class="hlt">crystallization</span> trials is then described, along with a protocol for confirming whether the <span class="hlt">crystals</span> obtained are composed of macromolecule as opposed to a <span class="hlt">crystallization</span> reagent . Next, the optimization of <span class="hlt">crystallization</span> conditions is presented. Finally, protocols that facilitate the growth of larger <span class="hlt">crystals</span> through <span class="hlt">seeding</span> are described. PMID:22045560</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeCoA.128..212O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeCoA.128..212O"><span>The surface reactivity of chalk (biogenic <span class="hlt">calcite</span>) with hydrophilic and hydrophobic functional groups</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Okhrimenko, D. V.; Dalby, K. N.; Skovbjerg, L. L.; Bovet, N.; Christensen, J. H.; Stipp, S. L. S.</p> <p>2014-03-01</p> <p>The surface properties of calcium carbonate minerals play an important role in a number of industrial and biological processes. Properties such as wettability and adsorption control liquid-solid interface behaviour and thus have a strong influence on processes such as biomineralisation, remediation of aquifers and oil recovery. We investigated how two model molecules of different polarity, namely water and ethanol, interact with reservoir and outcrop chalk samples and we compared their behaviour with that of pure, inorganically precipitated <span class="hlt">calcite</span>. Thermodynamic quantities, such as the work of wetting, surface energy and isosteric adsorption enthalpy, were determined from vapour adsorption isotherms. The chalks were studied fresh and after extraction of organic residues that were originally present in these samples. The work of wetting correlates with the amount of organic matter present in the chalk samples but we observed a fundamental difference between the adsorption properties of chalk and pure, inorganically precipitated <span class="hlt">calcite</span> toward the less polar, ethanol molecule. Further analysis of the chemical composition of the organic matter extracted from the chalk samples was made by gas chromatography (GC-MS). Monitoring surface composition by X-ray photoelectron spectroscopy (XPS) before and after extraction of the organic material, and with atomic force microscopy (AFM), showed that nanometer sized clay <span class="hlt">crystals</span> observed on the chalk particle surfaces could be an important part of the reason for the differences. Removal of the extractable portion of the hydrocarbons liberates adsorption sites that have different wetting properties than the rest of the chalk and these have an energy distribution that is similar to clays. Thus, the results exemplify the complexity of biogenic <span class="hlt">calcite</span> adsorption behaviour and demonstrate that chalk wetting in drinking water aquifers as well as oil reservoirs is controlled partly by the nanoparticles of clay that have grown on the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4142853','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4142853"><span>Direct nanoscale observations of the coupled dissolution of <span class="hlt">calcite</span> and dolomite and the precipitation of gypsum</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Cama, Jordi; Soler, Josep Maria; Putnis, Christine V</p> <p>2014-01-01</p> <p>Summary In-situ atomic force microscopy (AFM) experiments were performed to study the overall process of dissolution of common carbonate minerals (<span class="hlt">calcite</span> and dolomite) and precipitation of gypsum in Na2SO4 and CaSO4 solutions with pH values ranging from 2 to 6 at room temperature (23 ± 1 °C). The dissolution of the carbonate minerals took place at the (104) cleavage surfaces in sulfate-rich solutions undersaturated with respect to gypsum, by the formation of characteristic rhombohedral-shaped etch pits. Rounding of the etch pit corners was observed as solutions approached close-to-equilibrium conditions with respect to <span class="hlt">calcite</span>. The calculated dissolution rates of <span class="hlt">calcite</span> at pH 4.8 and 5.6 agreed with the values reported in the literature. When using solutions previously equilibrated with respect to gypsum, gypsum precipitation coupled with <span class="hlt">calcite</span> dissolution showed short gypsum nucleation induction times. The gypsum precipitate quickly coated the <span class="hlt">calcite</span> surface, forming arrow-like forms parallel to the crystallographic orientations of the <span class="hlt">calcite</span> etch pits. Gypsum precipitation coupled with dolomite dissolution was slower than that of <span class="hlt">calcite</span>, indicating the dissolution rate to be the rate-controlling step. The resulting gypsum coating partially covered the surface during the experimental duration of a few hours. PMID:25161860</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25649514','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25649514"><span>Fabrication of porous <span class="hlt">calcite</span> using chopped nylon fiber and its evaluation using rats.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ishikawa, Kunio; Tram, Nguyen Xuan Thanh; Tsuru, Kanji; Toita, Riki</p> <p>2015-02-01</p> <p>Although porous <span class="hlt">calcite</span> has attracted attention as bone substitutes, limited studies have been made so far. In the present study, porous <span class="hlt">calcite</span> block was fabricated by introducing chopped nylon fiber as porogen. Ca(OH)2 powder containing 10 wt% chopped nylon fiber was compacted at 150 MPa, and sintered to burn out the fiber and to carbonate the Ca(OH)2 under stream of 1:2 O2-CO2. Sintering of Ca(OH)2 at 750 °C or lower temperature resulted in incomplete burning out of the fiber whereas sintering at 800 °C or higher temperature resulted in the formation of CaO due to the thermal decomposition of Ca(OH)2. However, sintering at 770 °C resulted in complete burning out of the fiber and complete carbonation of Ca(OH)2 to <span class="hlt">calcite</span> without forming CaO. Macro- and micro-porosities of the porous <span class="hlt">calcite</span> were approximately 23 and 16%, respectively. Diameter of the macropores was approximately 100 μm which is suitable for bone tissue penetration. Porous <span class="hlt">calcite</span> block fabricated by this method exhibited good tissue response when implanted in the bone defect in femur of 12-weeks-old rat. Four weeks after implantation, bone bonded on the surface of <span class="hlt">calcite</span>. Furthermore, bone tissue penetrated interior to the macropore at 8 weeks. These results demonstrated the good potential value of porous <span class="hlt">calcite</span> as artificial bone substitutes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25161860','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25161860"><span>Direct nanoscale observations of the coupled dissolution of <span class="hlt">calcite</span> and dolomite and the precipitation of gypsum.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Offeddu, Francesco Giancarlo; Cama, Jordi; Soler, Josep Maria; Putnis, Christine V</p> <p>2014-01-01</p> <p>In-situ atomic force microscopy (AFM) experiments were performed to study the overall process of dissolution of common carbonate minerals (<span class="hlt">calcite</span> and dolomite) and precipitation of gypsum in Na2SO4 and CaSO4 solutions with pH values ranging from 2 to 6 at room temperature (23 ± 1 °C). The dissolution of the carbonate minerals took place at the (104) cleavage surfaces in sulfate-rich solutions undersaturated with respect to gypsum, by the formation of characteristic rhombohedral-shaped etch pits. Rounding of the etch pit corners was observed as solutions approached close-to-equilibrium conditions with respect to <span class="hlt">calcite</span>. The calculated dissolution rates of <span class="hlt">calcite</span> at pH 4.8 and 5.6 agreed with the values reported in the literature. When using solutions previously equilibrated with respect to gypsum, gypsum precipitation coupled with <span class="hlt">calcite</span> dissolution showed short gypsum nucleation induction times. The gypsum precipitate quickly coated the <span class="hlt">calcite</span> surface, forming arrow-like forms parallel to the crystallographic orientations of the <span class="hlt">calcite</span> etch pits. Gypsum precipitation coupled with dolomite dissolution was slower than that of <span class="hlt">calcite</span>, indicating the dissolution rate to be the rate-controlling step. The resulting gypsum coating partially covered the surface during the experimental duration of a few hours.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002A%26A...395L..29C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002A%26A...395L..29C"><span>Discovery of <span class="hlt">calcite</span> in the solar type protostar NGC 1333-IRAS 4</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ceccarelli, C.; Caux, E.; Tielens, A. G. G. M.; Kemper, F.; Waters, L. B. F. M.; Phillips, T.</p> <p>2002-11-01</p> <p>We present observations, obtained with ISO-LWS, of the continuum between 50-200 mu m of the solar type protostar IRAS 4, in the NGC 1333 complex. The continuum presents an excess, around 95 mu m, that we demonstrate must be a dust feature. We compared the 95 mu m excess with the <span class="hlt">calcite</span> feature at 92 mu m and find that it fits the observations reasonably well. There may be a further contribution from hydrous silicates at ~ 100 mu m, but this seems a less robust result. The detected <span class="hlt">calcite</span> mass is ~ 8 x 10-5 Msun and represents about 1% of the warm ( ~ 23 K) dust mass surrounding IRAS 4. This is only the second observation indicating the presence of carbonates outside the solar system, and the first revealing <span class="hlt">calcite</span> in a young protostar. It is remarkable and intriguing that in all the objects where <span class="hlt">calcite</span> has been detected so far, namely meteorites, planetary nebulae and IRAS 4, it represents from 0.3 to 1% of the dust mass. This new detection of <span class="hlt">calcite</span> strengthens the claim by Kemper et al. (2002a) that <span class="hlt">calcite</span> formation does not necessarely requires liquid water. We suggest that <span class="hlt">calcite</span> forms at the surface of the grains, where water ice layers may locally have an enhanced mobility caused by heating due to hard X-rays emitted by the central object.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeCoA.188..189C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeCoA.188..189C"><span>Uranium isotope fractionation during coprecipitation with aragonite and <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, Xinming; Romaniello, Stephen J.; Herrmann, Achim D.; Wasylenki, Laura E.; Anbar, Ariel D.</p> <p>2016-09-01</p> <p>Natural variations in 238U/235U of marine calcium carbonates might provide a useful way of constraining redox conditions of ancient environments. In order to evaluate the reliability of this proxy, we conducted aragonite and <span class="hlt">calcite</span> coprecipitation experiments at pH ∼7.5 and ∼8.5 to study possible U isotope fractionation during incorporation into these minerals. Small but significant U isotope fractionation was observed in aragonite experiments at pH ∼8.5, with heavier U isotopes preferentially enriched in the solid phase. 238U/235U of dissolved U in these experiments can be fit by Rayleigh fractionation curves with fractionation factors of 1.00007 + 0.00002/-0.00003, 1.00005 ± 0.00001, and 1.00003 ± 0.00001. In contrast, no resolvable U isotope fractionation was observed in an aragonite experiment at pH ∼7.5 or in <span class="hlt">calcite</span> experiments at either pH. Equilibrium isotope fractionation among different aqueous U species is the most likely explanation for these findings. Certain charged U species are preferentially incorporated into calcium carbonate relative to the uncharged U species Ca2UO2(CO3)3(aq), which we hypothesize has a lighter equilibrium U isotope composition than most of the charged species. According to this hypothesis, the magnitude of U isotope fractionation should scale with the fraction of dissolved U that is present as Ca2UO2(CO3)3(aq). This expectation is confirmed by equilibrium speciation modeling of our experiments. Theoretical calculation of the U isotope fractionation factors between different U species could further test this hypothesis and our proposed fractionation mechanism. These findings suggest that U isotope variations in ancient carbonates could be controlled by changes in the aqueous speciation of seawater U, particularly changes in seawater pH, PCO2 , Ca2+, or Mg2+ concentrations. In general, these effects are likely to be small (<0.13‰), but are nevertheless potentially significant because of the small natural range of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=fungicides+AND+agriculture&id=ED157731','ERIC'); return false;" href="http://eric.ed.gov/?q=fungicides+AND+agriculture&id=ED157731"><span><span class="hlt">Seed</span> Treatment. Bulletin 760.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Lowery, Harvey C.</p> <p></p> <p>This manual gives a definition of <span class="hlt">seed</span> treatment, the types of <span class="hlt">seeds</span> normally treated, diseases and insects commonly associated with <span class="hlt">seeds</span>, fungicides and insecticides used, types of equipment used for <span class="hlt">seed</span> treatment, and information on labeling and coloring of treated <span class="hlt">seed</span>, pesticide carriers, binders, stickers, and safety precautions. (BB)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=pesticide+AND+safety&pg=7&id=ED158978','ERIC'); return false;" href="http://eric.ed.gov/?q=pesticide+AND+safety&pg=7&id=ED158978"><span><span class="hlt">Seed</span> Treatment. Manual 92.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Missouri Univ., Columbia. Agricultural Experiment Station.</p> <p></p> <p>This training manual provides information needed to meet minimum EPA standards for certification as a commercial applicator of pesticides in the <span class="hlt">seed</span> treatment category. The text discusses pests commonly associated with <span class="hlt">seeds</span>; <span class="hlt">seed</span> treatment pesticides; labels; chemicals and <span class="hlt">seed</span> treatment equipment; requirements of federal and state <span class="hlt">seed</span> laws;…</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70016049','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70016049"><span>Activators of photoluminescence in <span class="hlt">calcite</span>: evidence from high-resolution, laser-excited luminescence spectroscopy</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Pedone, V.A.; Cercone, K.R.; Burruss, R.C.</p> <p>1990-01-01</p> <p>Laser-excited luminescence spectroscopy of a red-algal, biogenic <span class="hlt">calcite</span> and a synthetic Mn-<span class="hlt">calcite</span> can make the distinction between organic and trace-element activators of photoluminescence. Organic-activated photoluminescence in biogenic <span class="hlt">calcite</span> is characterized by significant peak shifts and increasing intensity with shorter-wavelength excitation and by significant decreases in intensity after heating to ??? 400??C. In contrast, Mn-activated photoluminescence shows no peak shift, greatest intensity under green excitation and limited changes after heating. Examination of samples with a high-sensitivity spectrometer using several wavelengths of exciting light is necessary for identification of photoluminescence activators. ?? 1990.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4996599','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4996599"><span>Recurrent Pure <span class="hlt">Calcite</span> Urolithiasis Confirmed by Endoscopic Removal and Infrared Spectroscopy in a Malnourished Anorectic Female</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Andreassen, Kim Hovgaard; Sloth Osther, Palle Jörn</p> <p>2016-01-01</p> <p>Abstract Often when <span class="hlt">calcite</span> is found as a component of urinary calculi, they are considered false calculi or artifacts. We present a case of true <span class="hlt">calcite</span> urolithiasis. The stone material was removed percutaneously from a severely malnourished anorectic woman and analyzed by infrared spectroscopy (IRS). In addition, <span class="hlt">calcite</span> urolithiasis was confirmed in several recurrent stone events by IRS. Laxative abuse with magnesium oxide was believed to be the underlying cause of stone formation, and ammonium chloride given as one weekly dose turned out to be effective for stone prevention. PMID:27579419</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1236222-alkaline-flocculation-phaeodactylum-tricornutum-induced-brucite-calcite','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1236222-alkaline-flocculation-phaeodactylum-tricornutum-induced-brucite-calcite"><span>Alkaline flocculation of Phaeodactylum tricornutum induced by brucite and <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Vandamme, Dries; Pohl, Philip I.; Beuckels, Annelies; ...</p> <p>2015-08-20</p> <p>Alkaline flocculation holds great potential as a low-cost harvesting method for marine microalgae biomass production. Alkaline flocculation is induced by an increase in pH and is related to precipitation of calcium and magnesium salts. In this study, we used the diatom Phaeodactylum tricornutum as model organism to study alkaline flocculation of marine microalgae cultured in seawater medium. Flocculation started when pH was increased to 10 and flocculation efficiency reached 90% when pH was 10.5, which was consistent with precipitation modeling for brucite or Mg(OH)2. Compared to freshwater species, more magnesium is needed to achieve flocculation (>7.5 mM). Zeta potential measurementsmore » suggest that brucite precipitation caused flocculation by charge neutralization. When calcium concentration was 12.5 mM, flocculation was also observed at a pH of 10. Furthermore, zeta potential remained negative up to pH 11.5, suggesting that precipitated <span class="hlt">calcite</span> caused flocculation by a sweeping coagulation mechanism.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4991261','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4991261"><span>Thin-film-induced morphological instabilities over <span class="hlt">calcite</span> surfaces</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Vesipa, R.; Camporeale, C.; Ridolfi, L.</p> <p>2015-01-01</p> <p>Precipitation of calcium carbonate from water films generates fascinating <span class="hlt">calcite</span> morphologies that have attracted scientific interest over past centuries. Nowadays, speleothems are no longer known only for their beauty but they are also recognized to be precious records of past climatic conditions, and research aims to unveil and understand the mechanisms responsible for their morphological evolution. In this paper, we focus on crenulations, a widely observed ripple-like instability of the the calcite–water interface that develops orthogonally to the film flow. We expand a previous work providing new insights about the chemical and physical mechanisms that drive the formation of crenulations. In particular, we demonstrate the marginal role played by carbon dioxide transport in generating crenulation patterns, which are indeed induced by the hydrodynamic response of the free surface of the water film. Furthermore, we investigate the role of different environmental parameters, such as temperature, concentration of dissolved ions and wall slope. We also assess the convective/absolute nature of the crenulation instability. Finally, the possibility of using crenulation wavelength as a proxy of past flows is briefly discussed from a theoretical point of view. PMID:27547086</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001GeoJI.144...96R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001GeoJI.144...96R"><span>Stress remagnetization in pyrrhotite-<span class="hlt">calcite</span> synthetic aggregates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Robion, Philippe; Borradaile, Graham J.</p> <p>2001-01-01</p> <p>Stress-induced remagnetization has been applied to multidomain pyrrhotite-<span class="hlt">calcite</span> synthetic aggregates in a triaxial rig. Experimental deformation used 150MPa confining pressure, a constant strain rate of 10-5 s-1 and applied differential stresses of up to 70MPa. New components of magnetization, parallel to the direction of the pressure vessel field, were added to the pre-deformational magnetization. The intensity of remagnetization (M'-M0) increases with the intensity of the applied differential stress and affects the coercivity fraction below 15mT. Bulk shortening is less than 8 per cent, thus grain rotation cannot explain selective remagnetization of the low-coercivity fraction. Remagnetization is thus attributed to deformational viscous remanent magnetization (DVRM). It is observed that high-coercivity (>15mT) grains do not remagnetize. There is, however, slight progressive rotation of pre-deformational magnetization with increasing strain up to 8 per cent of bulk shortening. The lack of piezoremanent magnetization in the high-coercivity range may be due to defects introduced in pyrrhotite during sample preparation. Experiments using synthetic pyrrhotite, expected to show low dislocation densities, would be necessary to test this effect.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19630003648&hterms=calcite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dcalcite','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19630003648&hterms=calcite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dcalcite"><span>Ultrasonic Observation of the <span class="hlt">Calcite</span>-Aragonite Transition</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ahrens, T. J.; Katz, S.</p> <p>1963-01-01</p> <p>Elastic-wave velocities were measured as a function of pressure by ultrasonic pulse Interferometry in Solenhofen and Manilus limestone specimens to pressures of 27 and 38 kb. Longitudinal velocities decrease sharply from 5.3 km/sec at a mean pressure of 4 kb to a minimum of 4.8 km/sec at 8 kb. Transverse velocities decrease from 3.1 to 2.9 km/sec. At the minimum bulk and rigidity moduli are 25 and 20 per cent below their 4-kb values. A density increase of 1.7 per cent is associated with this minimum. The observed effects are attributed to the <span class="hlt">calcite</span>-aragonite transition, and they may be due to an inherent property of the material, a component of which undergoes a polymorphic transition, the low- and high-pressure phases coexisting over a considerable pressure range. This may be an additional mechanism to account for low-velocity zones in the earth?s interior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1811382B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1811382B"><span>Nanoscale observations of the effect of citrate on calcium oxalate precipitation on <span class="hlt">calcite</span> surfaces.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Burgos-Cara, Alejandro; Ruiz-Agudo, Encarnacion; Putnis, Christine V.</p> <p>2016-04-01</p> <p>Calcium oxalate (CaC2O4ṡxH2O) minerals are naturally occurring minerals found in fossils, plants, kidney stones and is a by-product in some processes such as paper, food and beverage production [1,2]. In particular, calcium oxalate monohydrate phase (COM) also known as whewellite (CaC2O4ṡH2O), is the most frequently reported mineral phase found in urinary and kidney stones together with phosphates. Organic additives are well known to play a key role in the formation of minerals in both biotic and abiotic systems, either facilitating their precipitation or hindering it. In this regard, recent studies have provided direct evidence demonstrating that citrate species could enhance dissolution of COM and inhibit their precipitation. [3,4] The present work aims at evauate the influence of pH, citrate and oxalic acid concentrations in calcium oxalate precipitation on <span class="hlt">calcite</span> surfaces (Island Spar, Chihuahua, Mexico) through in-situ nanoscale observation using in situ atomic force microscopy (AFM, Multimode, Bruker) in flow-through experiments. Changes in calcium oxalate morphologies and precipitated phases were observed, as well as the inhibitory effect of citrate on calcium oxalate precipitation, which also lead to stabilization an the amorphous calcium oxalate phase. [1] K.D. Demadis, M. Öner, Inhibitory effects of "green"additives on the <span class="hlt">crystal</span> growth of sparingly soluble salts, in: J.T. Pearlman (Ed.), Green Chemistry Research Trends, Nova Science Publishers Inc., New York, 2009, pp. 265-287. [2] M. Masár, M. Zuborová, D. Kaniansky, B. Stanislawski, Determination of oxalate in beer by zone electrophoresis on a chip with conductivity detection, J. Sep. Sci. 26 (2003) 647-652. [3] Chutipongtanate S, Chaiyarit S, Thongboonkerd V. Citrate, not phosphate, can dissolve calcium oxalate monohydrate <span class="hlt">crystals</span> and detach these <span class="hlt">crystals</span> from renal tubular cells. Eur J Pharmacol 2012;689:219-25. [4] Weaver ML, Qiu SR, Hoyer JR, Casey WH, Nancollas GH, De Yoreo JJ</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1710009P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1710009P"><span>Control of carbonate alkalinity on Mg incorporation in <span class="hlt">calcite</span>: Insights on the occurrence of high Mg <span class="hlt">calcites</span> in diagenetic environments</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Purgstaller, Bettina; Mavromatis, Vasileios; Dietzel, Martin</p> <p>2015-04-01</p> <p>High Mg <span class="hlt">calcites</span> (HMC), with up to 25 mol % of Mg, are common features in early diagenetic environments and are frequently associated with bio-induced anaerobic oxidation of methane (AOM). Such archives hold valuable information about the biogeochemical processes occurring in sedimentary environments in the geological past. Despite the frequency AOM-induced HMC observed in marine diagenetic settings and their potential role in dolomitization, only a minor number of experimental studies has been devoted on deciphering their formation conditions. Thus, in order to improve our understanding on the formation mechanism of HMC induced by elevated carbonate ion concentrations, we precipitated HMC by computer controlled titration of a (Mg,Ca)Cl2 solution at different Mg/Ca ratios into a NaHCO3 solution under precisely defined physicochemical conditions (T = 25.00 ±0.03°C; pH = 8.3 ±0.1). The formation of carbonates was monitored at a high temporal resolution using in situ Raman spectroscopy as well as by continuous sampling and analyzing of precipitates and reactive solutions. We identified two distinct mechanisms of HMC formation. In solutions with molar Mg/Ca ratios ≤ 1/8 calcium carbonate was precipitated as crystalline phases directly from homogeneous solution. In contrast, higher Mg/Ca ratios induced the formation of Mg-rich ACC (up to 10 mol % of Mg), which was subsequently transformed to HMC with up 20 mol % of Mg. Our experimental results highlight that the finally formed HMC has a higher Mg content than the ACC precursor phase. Considering experimental data for Mg containing ACC transformation to crystalline calcium carbonate from literature, the continuous enrichment of Mg in the precipitate throughout transformation of amorphous to crystalline CaCO3 most likely occurs due to the high carbonate alkalinity (DIC about 0.1 M) of our reactive solutions. The Mg incorporation into <span class="hlt">calcite</span> lattice seems to be favored by intensive supply of carbonate ions as</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70010708','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70010708"><span>Some Debye temperatures from single-<span class="hlt">crystal</span> elastic constant data</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Robie, R.A.; Edwards, J.L.</p> <p>1966-01-01</p> <p>The mean velocity of sound has been calculated for 14 crystalline solids by using the best recent values of their single-<span class="hlt">crystal</span> elastic stiffness constants. These mean sound velocities have been used to obtain the elastic Debye temperatures ??De for these materials. Models of the three wave velocity surfaces for <span class="hlt">calcite</span> are illustrated. ?? 1966 The American Institute of Physics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JCrGr.373....2O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JCrGr.373....2O"><span>Structure of supersaturated solution and <span class="hlt">crystal</span> nucleation induced by diffusion</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ooshima, Hiroshi; Igarashi, Koichi; Iwasa, Hideo; Yamamoto, Ren</p> <p>2013-06-01</p> <p>The effect of a <span class="hlt">seed</span> <span class="hlt">crystal</span> on nucleation of L-alanine from a quiescent supersaturated solution was investigated. When a <span class="hlt">seed</span> <span class="hlt">crystal</span> was not used, nucleation did not occur at least for 5 h. When a <span class="hlt">seed</span> <span class="hlt">crystal</span> was introduced into the supersaturated solution with careful attention to avoid convection of the solution, fine <span class="hlt">crystals</span> appeared at the place far from the <span class="hlt">seed</span> <span class="hlt">crystal</span>. At that time, there was no convection at the place that fine <span class="hlt">crystals</span> appeared. Namely, there was no possibility that those fine <span class="hlt">crystals</span> came from the surface of <span class="hlt">seed</span> <span class="hlt">crystal</span>. We supposed that nucleation was induced by directional diffusion of solute molecules caused by growth of the <span class="hlt">seed</span> <span class="hlt">crystal</span>. In order to prove this hypothesis, we designed an experiment using an apparatus composed of two compartments divided by a dialysis membrane that L-alanine molecules could freely permeate. Two supersaturated solutions having a supersaturation ratio of 1.2 and a smaller ratio were placed in the two compartments in the absence of <span class="hlt">seed</span> <span class="hlt">crystals</span>. This apparatus allowed the directional diffusion of solute molecules between two solutions. Nucleation occurred within 30 min. The frequency of nucleation among 7-times repeated experiments was in proportion to the difference of supersaturation ratio between the two solutions. This result poses a new mechanism of the secondary nucleation that the directional diffusion caused by growth of existing <span class="hlt">crystals</span> induces nucleation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16566520','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16566520"><span>Effect of <span class="hlt">seeding</span> materials and mixing strength on struvite precipitation.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wang, Jun; Burken, Joel G; Zhang, Xiaoqi</p> <p>2006-02-01</p> <p>Struvite precipitation has increasing interest as a technology for removing and recovering phosphorus from wastewater streams. Many chemical factors have been studied, such as optimum pH values and component-ion molar ratios, yet, understanding of physical aspects is lacking. Two physical parameters were tested: (1) <span class="hlt">seeding</span> material addition and (2) mixing. Objectives were to evaluate three <span class="hlt">seeding</span> materials and to optimize mixing conditions for struvite-<span class="hlt">crystal</span> precipitation, growth, and subsequent sedimentation. Results confirm that mixing strength and proper <span class="hlt">seeding</span> materials increase <span class="hlt">crystal</span> size and improve settleability. For unseeded solutions, optimum phosphorus removal was achieved at a mixing strength of G = 76 s(-1). Struvite <span class="hlt">crystals</span> that were added as the <span class="hlt">seeding</span> material provided the best performance with respect to phosphorus removal and <span class="hlt">crystal</span>-size distribution. Overall, this study provided information to improve the practical application of struvite precipitation as a phosphorous-treatment technology for wastewaters, while generating a marketable slow-release fertilizer as a product.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22395925','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22395925"><span>Calcium sulfoaluminate (Ye'elimite) hydration in the presence of gypsum, <span class="hlt">calcite</span>, and vaterite</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hargis, Craig W.; Telesca, Antonio; Monteiro, Paulo J.M.</p> <p>2014-11-15</p> <p>Six calcium sulfoaluminate-based cementitious systems composed of calcium sulfoaluminate, <span class="hlt">calcite</span>, vaterite, and gypsum were cured as pastes and mortars for 1, 7, 28 and 84 days. Pastes were analyzed with X-ray diffraction, thermogravimetric and differential thermal analyses. Mortars were tested for compressive strength, dimensional stability and setting time. Furthermore, pastes with a water/cementitious material mass ratio of 0.80 were tested for heat evolution during the first 48 h by means of isothermal conduction calorimetry. It has been found that: (1) both <span class="hlt">calcite</span> and vaterite reacted with monosulfoaluminate to give monocarboaluminate and ettringite, with vaterite being more reactive; (2) gypsum lowered the reactivity of both carbonates; (3) expansion was reduced by <span class="hlt">calcite</span> and vaterite, irrespective of the presence of gypsum; and (4) both carbonates increased compressive strength in the absence of gypsum and decreased compressive strength less in the presence of gypsum, with vaterite's action more effective than that of <span class="hlt">calcite</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70015615','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70015615"><span>Simulation of <span class="hlt">calcite</span> dissolution and porosity changes in saltwater mixing zones in coastal aquifers</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Sanford, W.E.; Konikow, L.F.</p> <p>1989-01-01</p> <p>Thermodynamic models of aqueous solutions have indicated that the mixing of seawater and <span class="hlt">calcite</span>-saturated fresh groundwater can produce a water that is undersaturated with respect to <span class="hlt">calcite</span>. Mixing of such waters in coastal carbonate aquifers could lead to significant amounts of limestone dissolution. The potential for such dissolution in coastal saltwater mixing zones is analyzed by coupling the results from a reaction simulation model (PHREEQE) with a variable density groundwater flow and solute transport model. Idealized cross sections of coastal carbonate aquifers are simulated to estimate the potential for <span class="hlt">calcite</span> dissolution under a variety of hydrologic and geochemical conditions. Results show that limestone dissolution in mixing zones is strongly dependent on groundwater flux and nearly independent of the dissolution kinetics of <span class="hlt">calcite</span>. -from Authors</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=calcite+OR+montmorillonite+OR+kaolinite+OR+gibbsite&id=EJ213146','ERIC'); return false;" href="http://eric.ed.gov/?q=calcite+OR+montmorillonite+OR+kaolinite+OR+gibbsite&id=EJ213146"><span>High School Forum: "Invitations to Enquiry": The <span class="hlt">Calcite</span>/Acid Reaction.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Herron, J. Dudley, Ed.; Driscoll, D. R.</p> <p>1979-01-01</p> <p>Describes a high school chemistry experiment which involves the reaction between <span class="hlt">calcite</span> and hydrochloric and sulfuric acids. This reaction can be carried out as a projected demonstration and on an individual basis. (HM)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015MinPe.109..453G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015MinPe.109..453G"><span>Phase transformation of Mg-<span class="hlt">calcite</span> to aragonite in active-forming hot spring travertines</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Greer, Heather F.; Zhou, Wuzong; Guo, Li</p> <p>2015-08-01</p> <p>A travertine specimen collected from the western part of Yunnan Province of China was subjected to microstructural analysis by powder X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. A new formation mechanism was proposed whereby polycrystalline rhombohedral particles of magnesium-containing <span class="hlt">calcite</span> underwent a phase transformation into sheaf-like clusters of aragonite microrods. It is proposed that a high concentration of magnesium ions and embedded biological matter poisoned the growth of <span class="hlt">calcite</span> and therefore instigated the phase transformation of the core of the rhombohedral <span class="hlt">calcite</span> particles to an aragonite phase with a higher crystallinity. The single crystalline aragonite microrods with a higher density than the Mg-<span class="hlt">calcite</span> nanocrystallites grew at the expense of the latter to generate sheaf-like clusters. This newly discovered formation mechanism is expected to enhance previous knowledge on this geologically important phase transformation from a morphology point of view.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/12742051','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/12742051"><span>Polymer coatings to passivate <span class="hlt">calcite</span> from acid attack: polyacrylic acid and polyacrylonitrile.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Thompson, Mary; Wilkins, Shelley J; Compton, Richard G; Viles, Heather A</p> <p>2003-04-01</p> <p>The extent of passivation of <span class="hlt">calcite</span> toward dissolution by aqueous acids arising from polymeric coatings based on polyacrylic acid or polyacrylonitrile is evaluated using a channel flow cell technique with microdisc electrode detection. In situ passivation with polyacrylic acid leads to a reduction in the reactivity of <span class="hlt">calcite</span> toward acid attack with a reduction in the rate constant by up to an order of magnitude compared with untreated <span class="hlt">calcite</span>. Ex sit