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Sample records for calcite seed crystals

  1. The crystal structure of calcite III Joseph R. Smyth

    E-print Network

    Smyth, Joseph R.

    The crystal structure of calcite III Joseph R. Smyth Department of Geological Sciences, University of Technology, Pasadena, CA. Abstract. The crystal structure of calcite III has been deduced from existing high of the calcite I structure. The structure is monoclinic with space group C2 and a Z of 6. There are two Ca

  2. Brittlestar-inspired microlens arrays made of calcite single crystals.

    PubMed

    Ye, Xiaozhou; Zhang, Fei; Ma, Yurong; Qi, Limin

    2015-04-01

    Unique concave microlens arrays (MLAs) made of calcite single crystals with tunable crystal orientations can be readily fabricated by template-assisted epitaxial growth in solution without additives under ambient conditions. While the non-birefringent calcite (001) MLA showed excellent imaging performance like brittlestar's microlens arrays, the birefringent calcite (104) MLA exhibited remarkable polarization-dependent optical properties. PMID:25366272

  3. 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).

  4. Controlled calcite nucleation on polarized calcite single crystal substrates in the presence of polyacrylic acid

    NASA Astrophysics Data System (ADS)

    Wada, Norio; Horiuchi, Naohiro; Nakamura, Miho; Nozaki, Kosuke; Hiyama, Tetsuo; Nagai, Akiko; Yamashita, Kimihiro

    2015-04-01

    We studied theoretically and experimentally the effects of the surface electric field generated by polarization and polyacrylic acid (PAA) additives on the heterogeneous nucleation of calcite on the calcite single crystal substrates with (10.4), (10.0) and (00.1) orientations. A set of "in-situ" experiments with optical microscopy was performed to determine the waiting time of CaCO3 nucleation, defined as the time interval between the onset of the diffusion of CO2 and the appearance of the first visible precipitation. Calcite was nucleated on the oriented calcite substrates through diffusion of NH3 and CO2 gas from a solid ammonium carbonate into calcium chloride solutions. A theoretical analysis showed that the surface electric field of the polarized calcite substrate decrease the activation energy for nucleation and consequently promotes nucleation. Experimentally, the surface electric field and PAA addition were found to decrease both contact angles and waiting times, and as a result, promote the heterogeneous nucleation. Combined effect of PAA and surface electric field further reduced contact angles and waiting times regardless of orientation differences of the calcite substrates. The cooperation acts remarkably on N-surface of the respective calcite substrates. The results were explained by the Cassie's equation, a classical heterogeneous nucleation theory under a surface electric field, and matching of the charged sites on the PAA chain with the ion arrangement on the calcite substrate.

  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. Cross-section of Calcite Crystal Covering in Jewel Cave

    USGS Multimedia Gallery

    Jewel Cave is currently the 3rd most extensive cave network in the world. It is believed to have formed completely underwater, thus leading to the extensive coating of calcite crystals. A cross-sectional view of the crystal coating can be seen in the center of the image, with the surface of the cal...

  7. Synthesis of Calcite Single Crystals with Porous Surface by Templating of Polymer Latex Particles

    E-print Network

    Qi, Limin

    Synthesis of Calcite Single Crystals with Porous Surface by Templating of Polymer Latex Particles in solution. After template removal, well-defined, calcite single crystals exhibiting a rhombohedral morphology and uniform surface pores are obtained. The surface pore size of the calcite single crystals can

  8. Tip-Induced Calcite Single Crystal Nanowear Ramakrishna Gunda, and Alex A. Volinsky

    E-print Network

    Volinsky, Alex A.

    Tip-Induced Calcite Single Crystal Nanowear Ramakrishna Gunda, and Alex A. Volinsky Department Wear behavior of freshly cleaved single crystal calcite (CaCO3) was investigated by continuous scanning of effects. The wear regime is due to abrasive wear. Single crystal calcite hardness of 2.8±0.3 GPa

  9. Tetrahedral calcite crystals facilitate self-assembly at the air-water interface S. M. Hashmi

    E-print Network

    Tetrahedral calcite crystals facilitate self-assembly at the air-water interface S. M. Hashmi; published 26 October 2005 Calcite crystals often nucleate and grow in solutions of calcium carbonate out of aqueous solution is known to form fractal aggregates of micron-sized rhombohedral calcite

  10. Calcite crystal growth orientation: implications for trace metal uptake into coccoliths

    E-print Network

    Benning, Liane G.

    Calcite crystal growth orientation: implications for trace metal uptake into coccoliths V. E. PAYNE, OX1 3PR, UK ABSTRACT Inorganic calcite precipitation experiments were conducted to determine whether inducing specific orientations of calcite crystal growth can cause the enrichment of cations larger than Ca

  11. Selenium incorporation into calcite and its effect on crystal growth: An atomic force microscopy study

    E-print Network

    Montes-Hernandez, German

    Selenium incorporation into calcite and its effect on crystal growth: An atomic force microscopy December 2012 Available online 7 January 2013 Editor: J. Fein Keywords: Calcite Atomic force microscopy Crystal growth Selenium The atomic processes leading to calcite growth are still debated. The presence

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

    E-print Network

    Benning, Liane G.

    The kinetics and mechanisms of amorphous calcium carbonate (ACC) crystallization to calcite, via calcium carbonate (ACC) crystallization to calcite, via vaterite, were studied at a range, the vaterite transforms to calcite via a dissolution and reprecipitation mechanism with the reaction rate

  13. The grinding tip of the sea urchin tooth exhibits exquisite control over calcite crystal orientation

    E-print Network

    Gilbert, Pupa Gelsomina De Stasio

    The grinding tip of the sea urchin tooth exhibits exquisite control over calcite crystal 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

  14. 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

  15. 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.

  16. Journal of Crystal Growth 310 (2008) 29462953 Textural properties of synthetic nano-calcite produced by hydrothermal

    E-print Network

    Montes-Hernandez, German

    2008-01-01

    Journal of Crystal Growth 310 (2008) 2946­2953 Textural properties of synthetic nano-calcite to high temperature (30 and 90 1C) was used to synthesize fine particles of calcite. This method allows conditions have a strong influence on the crystal size and surface area of the synthesized calcite crystals

  17. 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 ? = 20, where ? = 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 ? = 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 (? >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 was established and maintained during the constant-composition experiments. CSDs having shapes intermediate between lognormal and Ostwald also were generated by varying the initial levels of supersaturation (initial ? = 28.2 to 69.2) in rapidly mixed solutions. Lognormal CSDs were observed for natural calcite crystals that are found in septarian concretions occurring in southeastern Colorado. Based on the model described above, these CSDs indicate initial growth by surface control, followed by supply-controlled growth. Thus, CSDs may be used to deduce crystal growth mechanisms from which geologic conditions early in the growth history of a mineral can be inferred. Conversely, CSD shape can be predicted during industrial crystallization by applying the appropriate conditions for a particular growth mechanism.

  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. Supporting Information Figure S1. Calcite crystals nucleated and grown on Kevlar threads in the absence of any

    E-print Network

    Coppersmith, Susan N.

    1 Supporting Information Figure S1. Calcite crystals nucleated and grown on Kevlar threads in the absence of any peptides or proteins. We define this as the negative control synthetic calcite. Please and SEM imaging techniques. Figure S2. Calcite crystals nucleated and grown on Kevlar threads

  1. Direct Observation of the Transition from Calcite to Aragonite Growth as Induced by Abalone Shell Proteins

    E-print Network

    Hansma, Paul

    Direct Observation of the Transition from Calcite to Aragonite Growth as Induced by Abalone Shell are known to cause the nucleation and growth of aragonite on calcite seed crystals in supersaturated with calcite crystals did not observe this transition because no information about the crystal polymorph

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    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.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. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr01568h

  3. Seed crystal Our Alamogordo was the biocontainment

    E-print Network

    Loss, Daniel

    FUTURES Seed crystal Our Alamogordo was the biocontainment laboratory on Wreckyn Street, and our seed-crystals and the animal's skin, and then a series of dainty cracks, like cellophane, as its carbon

  4. Measuring Carbon and Oxygen Isotope Uptake into Inorganic Calcite using Crystal Growth Experiments

    NASA Astrophysics Data System (ADS)

    Baker, E. B.; Watkins, J. M.

    2014-12-01

    Carbon and oxygen isotopes measured on natural calcite crystals provide a record of paleo-environment conditions. Despite the importance of measuring stable isotopes in calcite for paleo-environment reconstructions, there is neither a general theory nor an experimental data set that fully separates the effects of pH, temperature, and precipitation rate on isotope discrimination during calcite growth. Many stable isotope studies of calcite have focused on either carbon or oxygen isotope compositions individually, but few have measured both carbon and oxygen isotope uptake in the same set of crystals. We are precipitating inorganic calcite across a range in temperature, pH, and precipitation rate to guide the development of a general theory for combined carbon and oxygen isotope uptake into calcite crystals grown on laboratory timescales. In our experiments, dissolved inorganic carbon (DIC) is added to an aqueous solution (15 mM CaCl2 + 5 mM NH4Cl) by CO2 bubbling. Once a critical supersaturation is reached, calcite crystals nucleate spontaneously and grow on the beaker walls. A key aspect of this experimental approach is that the ?13C of DIC is relatively constant throughout the crystal growth period, because there is a continuous supply of DIC from the CO2-bearing bubbles. Carbonic anhydrase, an enzyme promoting rapid equilibration of isotopes between DIC and water, was added to ensure that the solution remained isotopically equilibrated during calcite growth. We have conducted experiments at T = 25°C and pH = 8.3 - 9.0. We observe that the fractionation of oxygen isotopes between calcite and water decreases with increasing pH, consistent with available data from experiments in which the enzyme carbonic anhydrase was used. Our results for carbon isotopes extend the available data set, which previously ranged from pH 6.62 to 7.75, to higher pH. At pH 8.3, we observe that calcite is isotopically heavier than DIC with respect to carbon isotopes by about 0.25‰. At pH 9.0, calcite is isotopically indistinguishable from, or perhaps slightly lighter than, DIC. We will present data from additional high-pH experiments and discuss the results in the context of recently developed ion-by-ion growth models for calcite.

  5. 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

    2013-08-01

    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. PMID:23787771

  6. 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.

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

    PubMed

    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

  8. 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

  9. 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.

  10. 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. PMID:26117783

  11. Direct observation of the transition from calcite to aragonite growth as induced by abalone shell proteins.

    PubMed Central

    Thompson, J B; Paloczi, G T; Kindt, J H; Michenfelder, M; Smith, B L; Stucky, G; Morse, D E; Hansma, P K

    2000-01-01

    The mixture of EDTA-soluble proteins found in abalone nacre are known to cause the nucleation and growth of aragonite on calcite seed crystals in supersaturated solutions of calcium carbonate. Past atomic force microscope studies of the interaction of these proteins with calcite crystals did not observe this transition because no information about the crystal polymorph on the surface was obtained. Here we have used the atomic force microscope to directly observe changes in the atomic lattice on a calcite seed crystal after the introduction of abalone shell proteins. The observed changes are consistent with a transition to (001) aragonite growth on a (1014) calcite surface. PMID:11106633

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

    NASA Astrophysics Data System (ADS)

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

    2003-06-01

    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.

  13. 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.

  14. 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. PMID:23320460

  15. 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.

  16. 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.

  17. 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

  18. Formation of star-shaped calcite crystals with Mg{sup 2+} inorganic mineralizer without organic template

    SciTech Connect

    Zhu Liying; Zhao Qingrui; Zheng Xiuwen; Xie Yi . E-mail: yxielab@ustc.edu.cn

    2006-04-15

    Star-shaped calcite crystals with 3-bar m symmetry were obtained in the mixed solvent of ethanol and H{sub 2}O (4:1vol%) using Mg{sup 2+} as grow mineralizer without any organic template under the solvothermal condition. The crystals branched to the six directions perpendicular to the c-axis. In the process, Mg{sup 2+} takes an important influence on such novel morphology via entering the crystal lattice of calcite to absorb the special plane and change the general growth habit. The aqueous solvent is favorable to form aragonite, while the presence of alcohol promotes the formation of calcite, the thermodynamically stable phase. The products were characterized by the techniques of XRD, SEM, SAED, IR and ICP. The formation process was also primarily studied.

  19. 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 depressed, giving rise to calcite "ghosts".

  20. 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.

  1. Applications of the streak seeding technique in protein crystallization

    NASA Astrophysics Data System (ADS)

    Stura, Enrico A.; Wilson, Ian A.

    1991-03-01

    The seeding of protein solutions is a powerful method for growing crystals. Microseeding and macroseeding both require conditions under which spontaneous nucleation is totally absent or extremely rare. A technique where seeds from a crystal are streaked into a protein-precipitant drop along a straight line using a rabbit whisker has been developed to determine suitable conditions for either micro- or macro-seeding. This seeding technique has also been successful in obtaining crystals using crystalline precipitate as the source of seeds, in cross-seeding from Fab—peptide complex crystals to obtain complexes with peptides of longer length, and similarly in cross-seeding from crystals of one monoclonal Fab—peptide complex to obtain crystals of a different monoclonal Fab complexed to the same peptide. This relatively simple technique should be of general applicability in macromolecular crystallizations and offers the potential to test whether new complex crystals mey be obtained by seeding with the native or other complexes, to determine whether cross-seeding may be used with seeds from a related protein or to analyze the crystallization potential of different protein preparations.

  2. Temperature-Controlled Support for a Seed Crystal

    NASA Technical Reports Server (NTRS)

    Reeve, J. L.

    1982-01-01

    A rodlike structure called a sting has been proposed for supporting a seed crystal at center of a body of saturated fluid and for controlling temperature/time profile of seed for experiments on crystal growth. Seed crystal is cooled or heated by thermoelectric modules while surrounding sheath remains at solution temperature. Heat is withdrawn to cooling fins by heat pipe, which replaces solid copper rod in a previous design.

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

    DOEpatents

    Montgomery, Kenneth E. (Tracy, CA); Zaitseva, Natalia P. (Livermore, CA); Deyoreo, James J. (Livermore, CA); Vital, Russell L. (Tracy, CA)

    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.

  4. Calcite growth kinetics: Modeling the effect of solution stoichiometry

    NASA Astrophysics Data System (ADS)

    Wolthers, Mariëtte; Nehrke, Gernot; Gustafsson, Jon Petter; Van Cappellen, Philippe

    2012-01-01

    Until recently the influence of solution stoichiometry on calcite crystal growth kinetics has attracted little attention, despite the fact that in most aqueous environments calcite precipitates from non-stoichiometric solution. In order to account for the dependence of the calcite crystal growth rate on the cation to anion ratio in solution, we extend the growth model for binary symmetrical electrolyte crystals of Zhang and Nancollas (1998) by combining it with the surface complexation model for the chemical structure of the calcite-aqueous solution interface of Wolthers et al. (2008). To maintain crystal stoichiometry, the rate of attachment of calcium ions to step edges is assumed to equal the rate of attachment of carbonate plus bicarbonate ions. The model parameters are optimized by fitting the model to the step velocities obtained previously by atomic force microscopy (AFM, Teng et al., 2000; Stack and Grantham, 2010). A variable surface roughness factor is introduced in order to reconcile the new process-based growth model with bulk precipitation rates measured in seeded calcite growth experiments. For practical applications, we further present empirical parabolic rate equations fitted to bulk growth rates of calcite in common background electrolytes and in artificial seawater-type solutions. Both the process-based and empirical growth rate equations agree with measured calcite growth rates over broad ranges of ionic strength, pH, solution stoichiometry and degree of supersaturation.

  5. 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. PMID:23507262

  6. 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

  7. 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)

  8. 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. PMID:24302723

  9. 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. PMID:23896564

  10. 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. PMID:26348458

  11. 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.

  12. Hydration of Cuphea seeds containing crystallized triacylglycerols

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Seeds that exhibit intermediate storage behavior do not appear to survive under conventional -18C storage conditions. Cuphea wrightii, C. laminuligera, C. carthagenensis, and C. aequipetala are considered sensitive to low temperature storage. The seeds of these species have triacylglycerols (TAG) ...

  13. Evolution and the Calcite Eye Lens

    E-print Network

    Williams, Vernon L

    2013-01-01

    Calcite is a uniaxial, birefringent crystal, which in its optically transparent form, has been used for animal eye lenses, the trilobite being one such animal. Because of the calcite birefringence there is a difficulty in using calcite as a lens. When the propagation direction of incoming light is not exactly on the c-axis, the mages blur. In this paper, calcite blurring is evaluated, and the non-blurring by a crystallin eye lens is compared to a calcite one.

  14. Evolution and the Calcite Eye Lens

    E-print Network

    Vernon L. Williams

    2013-04-03

    Calcite is a uniaxial, birefringent crystal, which in its optically transparent form, has been used for animal eye lenses, the trilobite being one such animal. Because of the calcite birefringence there is a difficulty in using calcite as a lens. When the propagation direction of incoming light is not exactly on the c-axis, the mages blur. In this paper, calcite blurring is evaluated, and the non-blurring by a crystallin eye lens is compared to a calcite one.

  15. Uranyl incorporation in natural calcite.

    SciTech Connect

    Kelly, S. D.; Newville, M. G.; Cheng, L.; Kemner, K. M.; Sutton, S. R.; Fenter, P.; Sturchio, N. C.; Spotl, C.; Environmental Research; Univ. of Chicago; Univ. of Illiois at Chicago; Univ. of Innsbruck

    2003-01-01

    The occurrence of trace amounts of uranyl in natural calcite has posed a long-standing problem in crystal chemistry because of speculation that the size and shape of the uranyl ion may preclude its incorporation in a stable lattice position in calcite. This also defines an important environmental problem because of its bearing on the transport and sequestration of uranyl released from nuclear facilities and uranium mining operations. Calcite is a nearly ubiquitous mineral in soils and groundwater aquifers. X-ray absorption spectroscopy and X-ray fluorescence microprobe studies of uranium in relatively U-rich {approx}13700-year-old calcite from a speleothem in northernmost Italy indicate substitution of uranyl for a calcium and two adjacent carbonate ions in calcite. These new data imply that uranyl has a stable lattice position in natural calcite, indicating that it may be reliably sequestered in calcite over long time scales.

  16. 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.

  17. 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 (?) 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.

  18. Growth of silicon carbide crystals on a seed while pulling silicon crystals from a melt

    NASA Technical Reports Server (NTRS)

    Ciszek, T. F.; Schwuttke, G. H. (inventor)

    1979-01-01

    A saturated solution of silicon and an element such as carbon having a segregation coefficient less than unity is formed by placing a solid piece of carbon in a body of molten silicon having a temperature differential decreasing toward the surface. A silicon carbide seed crystal is disposed on a holder beneath the surface of the molten silicon. As a rod or ribbon of silicon is slowly pulled from the melt, a supersaturated solution of carbon in silicon is formed in the vicinity of the seed crystal. Excess carbon is emitted from the solution in the form of silicon carbide which crystallizes on the seed crystal held in the cool region of the melt.

  19. BACTERIALLY-INDUCED DISSOLUTION OF CALCITE

    E-print Network

    BACTERIALLY-INDUCED DISSOLUTION OF CALCITE: THE ROLE OF BACTERIA IN LIMESTONE WEATHERING Fatimah The interaction between microorganisms and the calcite mineral surface in aqueous solutions, under earth surface and metabolism increase the dissolution rates of calcite crystals and alter their surfaces in solution. A natural

  20. Variations in the Sr/Ca, ?44Ca and ?18O composition of calcite as a function of solution chemistry and crystal growth rate

    NASA Astrophysics Data System (ADS)

    Watkins, J. M.; DePaolo, D. J.; Ryerson, F. J.

    2012-12-01

    The trace element and isotopic composition of calcite can be used to probe the temperatures and rates of mineral formation as well as the degree of post-mineralization alteration. The accuracy with which these effects can be interpreted is limited by our ability to distinguish signatures arising from equilibrium partitioning versus kinetic or mass transport effects. Our focus in this work is on mass transport effects in aqueous environments, and specifically, the growth rate-dependence of trace element and isotopic incorporation into calcite. This requires experiments in which the degree of supersaturation, or the solution chemistry, is held constant and the rate of crystal growth can be determined. In our experiments, N2+CO2 gas mixture is bubbled through a beaker containing 1300 mL of solution (30 mM CaCl2 + 5 mM NH4Cl + 0.1 mM SrCl2). The degree of supersaturation with respect to calcite is controlled by the pCO2 of the gas mixture, which is constantly replenished from a gas source. As CO2 from the gas dissolves into solution, calcite crystals grow on the beaker walls and the pH of the solution is maintained by use of an autotitrator with NaOH as the titrant. During an experiment we control the temperature, pH, the pCO2 of the gas inflow, and the gas inflow rate. At the same time we monitor the total alkalinity, the pCO2 of the gas outflow, the gas outflow rate, and the amount of NaOH added. The rate of calcite precipitation can be determined in three ways: (1) the change in total alkalinity due to Ca2+ removal, mass balance of C in the system, and (3) post-run measurement of [Ca2+] in aliquots of solution taken during an experiment. We present results from experiments where growth rates are estimated to range from 0.5 to 16 mmol/m2/hr. Our experiments thus far have yielded calcite crystals that are out of calcium and oxygen isotopic equilibrium with the parent solution. Crystals are enriched in the light isotope of Ca by 0.4 to 1.8‰. The light isotope enrichment increases with growth rate and is correlated with Sr/Ca in calcite. These results are in excellent agreement with the results of Tang et al. (2008) for crystals grown at 25°C and suggest that mass discrimination is controlled by mass transport kinetics at the mineral-solution interface. Oxygen isotopes are more complicated because of the addition of CO2 to the bulk solution. For crystals grown from our stock solution, the O composition is highly variable and not correlated with growth rate. We attribute this to relatively slow kinetics of O isotope exchange between gaseous or dissolved CO2 and water. For crystals grown in the presence of 0.01 grams of bovine carbonic anhydrase (CA), an enzyme which catalyzes the interconversion of CO2 and H2O to bicarbonate and protons, the O isotope composition of calcite appears to be independent of growth rate. Hence addition of CA to solution might offer a means of determining the equilibrium fractionation factor for oxygen isotopes in carbonate minerals. We will present results from additional experiments that test how CA and other organic molecules in solution affect the growth rate and mass discrimination during mineral precipitation.

  1. MASSIVE CELLULAR DISRUPTION OCCURS DURING EARLY IMBIBITION OF CUPHEA SEEDS CONTAINING CRYSTALLIZED TRIACYLGLYCEROLS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The transition from anhydrobiotic to hydrated state occurs during early imbibition of seeds and is lethal if lipid reserves in seeds are crystalline. Lipids are crystallized by low temperatures used during seed storage. Here, we examine the nature of cellular damage observed in seeds of Cuphea wrig...

  2. 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 ? ? 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.

  3. Isothermal Crystallization Kinetics of Mango (Mangifera indica) Almond Seed Fat

    NASA Astrophysics Data System (ADS)

    Solis-Fuentes, J. A.; Hernandez-Medel, M. R.; Duran-de-Bazua, M. C.

    In this study, the kinetics of isothermal crystallization of mango (Mangifera indica) almond seed fat var. Manila (MAF) was analyzed, within the theoretical context of the Sestak-Berggren model, the Avrami Equation and its modification by Khanna and Taylor. The results showed that the induction times for the formation of crystalline nuclei increased with the crystallization temperature (3.3 min at 8°C and 10.9 min at 12°C). The supercooling level notably influenced the MAF crystallization rate, since the global constant of crystallization rate, Z, grew 3.3 times from 12 to 8°C (for fractions of fat solids between 0.25 and 0.75, Z was 0.2904, 0.1584 and 0.0879 min-1 at 8, 10 and 12°C, respectively) and the Avrami parameter r was higher than 4; this demonstrates the effect of fat system complexity due to its multi-component nature and the heterogeneous character of this crystallization process, which includes additional participation of nucleation sites. The modified model by Khanna and Taylor provided better parametral values than the other two studied for explaining MAF crystallization kinetic.

  4. Controlled Growth of Micropatterned, Oriented Calcite Films on a Self-Assembled Multilayer Film

    E-print Network

    Qi, Limin

    Controlled Growth of Micropatterned, Oriented Calcite Films on a Self-Assembled Multilayer Film of calcium carbonate. Micropatterned CaCO3 films consisting of regularly aligned calcite crystals oriented successfully used for the formation of ordered calcite crystal arrays,7a,b pat- terned calcite single crystals

  5. & Microarrays Calcite Microneedle Arrays Produced by Inorganic Ion-Assisted

    E-print Network

    Qi, Limin

    & Microarrays Calcite Microneedle Arrays Produced by Inorganic Ion-Assisted Anisotropic Dissolution of Bulk Calcite Crystal Xia Long,[a] Ruijie Meng,[b] Weike Wu,[c] Yurong Ma,*[a] Dong Yang,[b] and Limin and fabricate crystals with complicated morphologies. The formation of ordered arrays of c-axis-oriented calcite

  6. 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.

  7. Modification of calcite crystal morphology by designed phosphopeptides and primary structures and substrate specifities of the cysteine proteases mexicain and chymomexicain

    NASA Astrophysics Data System (ADS)

    Lian, Zhirui

    In order to better understand the mechanism of biomineralization, we have undertaken to synthesize polypeptide model compounds of well-defined structure that can interact with specific faces of calcite and alter its crystal morphology. These peptides were designed based on the structure of alpha-helical winter flounder antifreeze polypeptide HPLC-6. In these peptides, from one to three of the threonine residues in HPLC-6 were substituted by phosphoserine or phosphotyrosine. CD spectra show that all the peptides have virtually the same alpha-helicity, i.e., about 90% at 4°C and 50% at 25°C. However, only peptides which contain at least two phosphate groups spaced 16.8-A apart can modify the crystal morphology of the calcite. The newly developed surface has been tentatively identified as the (001) basal face. Molecular modeling indicates that the spacing of phosphate groups allows for a good match with crystal lattice ions on the (001) plane. Another peptide, CBP-3D, in which the three threonine residues in HPLC-6 were substituted by aspartic acids, appears to bind only to {104} rhombohedral faces of calcite. These experiments suggest that conformation and orientation of the binding ligands in the peptide are important factors governing the mutual recognition of crystal surface and proteins. The complete amino acid sequences of the cysteine proteases mexicain and chymomexicain, isolated from the latex of the plant Pileus mexicanus , were determined by Edman degradation of proteolytic fragments. Mexicain and chymomexicain show-high sequence homology to the papain family of cysteine protease. Mexicain and chymomexicain are monomeric polypeptides, with molecular masses of 23,762 Da and 23,694 Da, respectively, and both contain three deduced disulfide bonds. The proteolytic substrate specificities of mexicain and chymomexicain were studied by digesting a series of synthetic peptides and analyzing the fragments by mass spectrometry. The two proteases showed virtually the same substrate specificity, having a rather broad specificity, but with some preference for Val, Thr, Phe, Tyr and Leu at the P2 position. However, they do not appear to cleave peptide bonds where P2 is Lys, Arg or Ile. Their computated 3-dimensional structures were found to be nearly identical to papain and related proteins by homology modeling.

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

    DOEpatents

    Todt, Volker (Lemont, IL); Miller, Dean J. (Darien, IL); Shi, Donglu (Oak Park, OH); Sengupta, Suvankar (Columbus, OH)

    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.

  9. 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

  10. 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.

  11. 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.

  12. 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 ?m. 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, ?, 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 within variable-aperture fields will investigate the dependency of growth patterns on heterogeneous aperture distributions. (a) Aperture strain (?b/bi) after 14 days. Precipitation is concentrated near the inlet and decreases in the flow direction. (b) Width-averaged profiles of the initial and final aperture field show changes in aperture and smoothing that results from calcite precipitation between the initial discrete crystals.

  13. 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 into calcite under non-equilibrium conditions. Adaptation of the model for clumped isotope uptake under non-equilibrium conditions requires knowledge of the clumped isotopic compositions of DIC species and any mass-dependent kinetic fractionation that arises during ion transport to or from the mineral surface.

  14. Zinc isotope fractionation during adsorption on calcite

    NASA Astrophysics Data System (ADS)

    Dong, S.; Wasylenki, L. E.

    2013-12-01

    Zinc is an important element as a nutrient in the marine biosphere. However, our understanding of its biogeochemical cycling in the oceans is relatively limited. The Zn stable isotope system holds the promise of providing novel insights, since published Zn isotopic values for various natural samples reveal significant fractionations in the marine environment. Surface seawater, basalts, shales, deep-sea clay sediments, sediment trap material, bulk plankton and zooplankton samples, and eolian dust fall within a tight range (?66/64Zn from -0.1 to 0.5‰), but modern ferromanganese crusts (?66/64Zn from 0.5 to 1.2‰), as well as carbonates (?66/64Zn from 0.3 to 1.4‰), are notably enriched in heavy Zn isotopes [1-4]. In this study we seek to constrain the mechanism by which carbonates are enriched in heavier isotopes. In particular, we have conducted experiments to quantify isotope fractionation during adsorption of Zn onto the surfaces of calcite crystals that are in equilibrium with solution. The adsorption experiments were carried out in a series of small-volume batch reactions in a clean laboratory environment, using high-purity reagents and calcite seed crystals. The calcite was equilibrated with the solution prior to addition of Zn at atmospheric CO2 pressure (i.e., in air) for 5 days until a stable pH of 8.3 was reached. Later, a small aliquot of dissolved ZnCl2 was added such that the solution remained undersaturated with respect to hydrozincite. Experimental duration varied among the replicates from 6 to 144 hours, and then all solids and solutions were separated by filtration, purified by ion exchange chromatography, and analyzed by MC-ICP-MS. Zn adsorbed on calcite is isotopically heavier than in the co-existing solutions, with ?68/66Zncalcite-solution of approximately 0.3‰. The variation of ?68/66Zncalcite-solution beyond 24 hours is insignificant, so we infer that isotopic equilibrium is reached by this time. Previous work strongly suggests that a difference in coordination number between dissolved Zn and adsorbed Zn is drives the observed fractionation. Elzinga and Reeder[5] determined using EXAFS (Extended X-ray Absorption Fine Structure) that Zn adsorbed to calcite surfaces is tetrahedrally coordinated, sharing three oxygens with the calcite surface. Meanwhile density functional theory calculations[6] predicted that tetrahedral Zn-O species should be heavier than octahedral Zn-O species. Thus we infer that equilibrium between octahedrally coordinated, dissolved Zn and tetrahedrally coordinated, adsorbed Zn is the mechanism of fractionation in our experiments. Our further studies will determine whether the isotopically heavy pool of adsorbed Zn becomes the Zn incorporated within carbonates; if so, then we are closer to understanding the mechanism by which carbonate rocks in nature are enriched in heavier isotopes of zinc. [1] Bermin et al., 2006, Chem. Geol. 226, 280. [2] Maréchal et al., 2000, Geochem. Geophys. Geosyst. 1, 1999GC-000029. [3] Dong et al., 2013, Talanta 114, 103-109. [4] Pichat et al., 2003, Earth Planet. Sci. Lett. 210, 167-178. [5] Elzinga and Reeder, 2002, Geochim. Cosmochim. Acta 66, 3943-3954. [6] Schauble, 2003, EOS, Trans. AGU, Fall Meet. Suppl. 84(46), B12B-0781.

  15. 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...

  16. Oriented Calcite Micropillars and Prisms Formed through Aggregation and Recrystallization of Poly(Acrylic Acid) Stabilized

    E-print Network

    Qi, Limin

    Oriented Calcite Micropillars and Prisms Formed through Aggregation and Recrystallization of Poly crystallization of one-dimensional (1D) calcite microstructures along defined crystallographic axes is poorly) and calcite substrates we can direct the formation of calcite through an intermediate complex of PAA and Ca2

  17. Modeling microbially induced calcite precipitation

    E-print Network

    Cirpka, Olaf Arie

    Modeling microbially induced calcite precipitation Erlangen, November 27th 2014 Johannes Hommel Induced Calcite Precipitation (MICP) is investigated as sealing technology. It is used as an exemplary / detachment · Urea hydrolysis · Precipitation / dissolution of calcite · Clogging calcite precipitate CO2

  18. Combining site-specific mutagenesis and seeding as a strategy to crystallize ‘difficult’ proteins: the case of Staphylococcus aureus thioredoxin

    SciTech Connect

    Roos, Goedele; Brosens, Elke; Wahni, Khadija; Desmyter, Aline; Spinelli, Silvia; Wyns, Lode; Messens, Joris; Loris, Remy

    2006-12-01

    S. aureus thioredoxin was crystallized using a combination of seeding and site-specific mutagenesis. The P31T mutant of Staphylococcus aureus thioredoxin crystallizes 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 crystals diffract to 2.2 Å resolution. Isomorphous crystals of wild-type thioredoxin as well as of other point mutants only grow when seeded with the P31T mutant. These results suggest seeding as a valuable tool complementing surface engineering for proteins that are hard to crystallize.

  19. 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.

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

    PubMed Central

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

    2015-01-01

    Sirtuins constitute a family of NAD+-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. PMID:26625292

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

    PubMed

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

    2015-12-01

    Sirtuins constitute a family of NAD(+)-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. PMID:26625292

  2. 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.

  3. 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.

  4. Microrobotic Streak Seeding For Protein Crystal Growth CUCS04104

    E-print Network

    shift biologists' focus toward proteins, the product genes. A large coordinated e#ort under way. strategies tools automated manipulation of protein crystals, one most popular methods for structure determination X­ray crystallography [NRK + 00]. Automated protein crystal manipulation is a challenging because

  5. Growth of GaN:Mg crystals by high nitrogen pressure solution method in multi-feed-seed configuration

    NASA Astrophysics Data System (ADS)

    Grzegory, I.; Bo?kowski, M.; ?ucznik, B.; Weyher, J.; Litwin-Staszewska, E.; Konczewicz, L.; Sadovyi, B.; Nowakowski, P.; Porowski, S.

    2012-07-01

    Crystallization of GaN by High Nitrogen Pressure Solution method in multi-feed-seed (MFS) configuration without intentional doping [1] results in: (1) Growth of strongly n-type crystals with free electron concentration increasing with growth temperature in ranges of 2-6×1019 cm-3 and 1350-1430 °C, (2) stable growth on Ga-polar surface and unstable growth on N-polar surface, crystals slightly brown, (3) improvement of (0001) crystallographic planes curvature (flattening) with respect to bowing of these planes in the seed crystals. The addition of magnesium into the growth solution causes strong compensation of free electrons in the crystals. Therefore, highly resistive GaN crystals can be grown. In this work, the crystallization of Mg doped GaN on flat ?1 in. seeds (substrates) grown by HVPE in MFS configuration has been studied. It is shown that: (1) Highly resistive GaN:Mg crystals with resistivity higher than 107 ? cm were grown, (2) the growth is stable on N-polar surfaces of the seeds whereas it is unstable on the Ga-polar surfaces, which is opposite to the HNPS growth of the n-type crystals. The GaN:Mg crystals are fully transparent with no visible color, (3) shape of (0001) crystallographic planes improves (flattens) with respect to bowing of these planes in the seed crystals (HVPE substrates).

  6. In-situ Ar-Ar white mica ages reveal differences in mica crystallization behaviour in quartz-rich and calcite-rich rocks of the same shear zone

    NASA Astrophysics Data System (ADS)

    Cossette, Élise; Schneider, David; Warren, Clare; Grasemann, Bernhard

    2013-04-01

    Conventional Ar-Ar dating of tectonites can result in equivocal ages due to mixed mineral populations, excess 40Ar (decoupled from its parent 40K), or partial resetting of the K-Ar systematics. In-situ Ar-Ar dating was performed on white micas from footwall marbles and schists of the Western Cycladic Detachment System (WCDS) of the Aegean. These rocks are part of the Cycladic Blueschist Unit, which experienced HP conditions during the Eocene and strong extension during the Miocene. The rocks contain undeformed, kinked, and neocrystallized micas with the mica phases recording higher strain (elongated grains and mica-fish structures) in quartz-dominated rocks compared to the calcite-dominated assemblages. In both quartzitic and calcitic rocks, deformed white micas are chemically zoned. Two chemical populations were identified: (1) a high component of Al-celadonite in undeformed portions of grains that likely crystallized during high pressure metamorphism; (2) enrichment in muscovite in deformed portions of grains as a result of Tschermak substitution that took place during deformation-induced neocrystallization under shallow crustal conditions. Neocrystallization occurs preferentially in zones of localized deformation and in zones of enhanced fluid availability. The latter is supported by stable isotope (O, C, H) analyses of calcite, dolomite and white micas that suggest a moderate fluid-rock interaction resulting in a coupled depletion of ?18O vs ?13C and ?18O vs ?D. Recrystallized quartz exhibits planar indentation structures, also consistent with fluid-assisted deformation. Completely neocrystallized grains, in quartzitic rocks from Kea Island at the center of the WCDS yield Ar-Ar deformation ages of c. 18-21 Ma, which are interpreted as dating the timing of ductile extension along the detachment system. Undeformed (unkinked, prismatic) portions of white micas in calcitic rocks from Serifos Island at the southern end of the WCDS yield Ar-Ar ages of c. 40-45 Ma, whereas deformed (kinked or strained) portions of the same grains yield younger ages of c. 31-36 Ma. Calcitic rocks are intrinsically less permeable than quartzitic rocks, thus are less affected by fluid-induced recrystallization. Moreover, in calcite-muscovite aggregates, strain is accommodated in calcite (by dislocation creep) whereas in quartz-muscovite aggregates, strain is accommodated in mica (as mica-fish structures). Hence, ductily deformed and completely neocrystallized micas occur more often in quartzitic rocks, whereas calcitic rocks contain micas that are only partially neocrystallized due to a lack of deformation and fluid infiltration. Consequently, consistent with our empirical results, the minimum age of ductile deformation is more likely to be preserved in quartzitic rocks, such as the c. 18-21 Ma obtained on Kea. Similarly, inherited or partially reset ages are likely to be found in calcitic rocks, such as the c. 31-36 Ma from Serifos.

  7. Diffusion of Ca and Mg in Calcite

    SciTech Connect

    Cygan, R.T.; Fisler, D.K.

    1999-02-10

    The self-diffusion of Ca and the tracer diffusion of Mg in calcite have been experimentally measured using isotopic tracers of {sup 25}Mg and {sup 44}Ca. Natural single crystals of calcite 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 calcite is relatively slow and cations are the rate-limiting diffusing species for the deformation of calcite and carbonate rocks. Application of the calcite-dolomite geothermometer to metamorphic assemblages will be constrained by cation diffusion and cooling rates. The direct measurement of Mg tracer diffusion in calcite indicates that dolomitization is unlikely to be accomplished by Mg diffusion in the solid state but by a recrystallization process.

  8. Optical, structural, thermal and dielectric spectroscopy characterizations of seeded melt grown 2-hydroxy biphenyl single crystal.

    PubMed

    Sadhasivam, S; Rajesh, Narayana Perumal

    2014-09-15

    Organic single crystal of 2-hydroxy biphenyl (2-HB) was grown by top seeded melt growth method. Scanning electron microscopy studies has been carried out on the surface of the grown crystals to investigate the nature of growth and defects. The crystalline perfection and lattice parameters of 2-HB has been determined by single crystal XRD analysis and it belongs to orthorhombic crystal system with space group Fdd2. The functional groups and molecular associations were confirmed by FT-IR. The optical characteristics such as cut-off and transmittance were carried out using UV-Vis-NIR spectra. Absence of absorption in the region between 320 and 1100 nm makes the grown crystal desirable to optical applications. Thermal stability of grown crystals was characterized by thermogravimetric (TGA), differential thermal analysis (DTA) and differential scanning calorimetric (DSC) analyses. Broadband dielectric studies reveals that dielectric constant of grown crystal is low. The resistivity of grown crystal was studied by impedance analysis. The second harmonic generation intensity of 3.8 mJ was studied. The grown crystal belongs to soft material studied by hardness test. PMID:24792201

  9. Biogenic and synthetic high magnesium calcite - a review.

    PubMed

    Long, Xia; Ma, Yurong; Qi, Limin

    2014-01-01

    Systematic studies on the Mg distributions, the crystal orientations, the formation mechanisms and the mechanical properties of biogenic high-Mg calcites in different marine organisms were summarized in detail in this review. The high-Mg calcites in the hard tissues of marine organisms mentioned generally own a few common features as follows. Firstly, the Mg distribution is not uniform in most of the minerals. Secondly, high-Mg calcite biominerals are usually composed of nanoparticles that own almost the same crystallographic orientations and thus they behave like single crystals or mesocrystals. Thirdly, the formation of thermodynamically unstable high-Mg calcites in marine organisms under mild conditions is affected by three key factors, that is, the formation of amorphous calcium (magnesium) carbonate precursor, the control of polymorph via biomolecules and the high Mg/Ca ratios in modern sea. Lastly, the existence of Mg ions in the Mg-containing calcite may improve the mechanical properties of biogenic minerals. Furthermore, the key progress in the synthesis of high-Mg calcites in the laboratory based on the formation mechanisms of the biogenic high-Mg calcites was reviewed. Many researchers have realized the synthesis of high-Mg calcites in the laboratory under ambient conditions with the help of intermediate amorphous phase, mixed solvents, organic/inorganic surfaces and soluble additives. Studies on the structural analysis and formation mechanisms of thermodynamically unstable biogenic high-Mg calcite minerals may shed light on the preparation of functional materials with enhanced mechanical properties. PMID:24291472

  10. Mineralogcial Biosignature of High-Magnesian Calcite

    NASA Astrophysics Data System (ADS)

    Zhang, F.; Konishi, H.; Xu, H.; Roden, E. E.

    2008-12-01

    Some dolomite formations are associated with sediments where sulfate reduction is active. In general, sulfate has been considered to inhibit dolomite formation. However, it was also suggested that the reaction products of sulfate reduction, such as increased alkalinity, may play a more important role in increasing the formation rate of dolomite than sulfate does in inhibiting it. We have investigated the effect of sulfide on Mg-Ca carbonate precipitation. Our results show that high-magnesian calcite which contains as much as 34 mol% magnesite can precipitate from solutions with the presence of certain amount of dissolved sulfide and pyrite crystals. These high-magnesian calcites form unusual micro-scale spheres with cracks on them. High- resolution SEM and TEM results show that these spheres are actually composed of a great number of nano- crystals (~50 nm) stacking together with low-angle grain boundaries. Both synthesized and natural high-magnesian calcites indicate that dissolved and solid sulfides can catalyze the Mg incorporation into calcite lattice. We hypothesize that S2- (or HS-) ions and >S2 on pyrite surface will decrease the hydration / slovation energy of magnesium ions and thus promote nucleation and crystallization of the high-magnesian calcite. In nature environment, the sulfide could be related to microbe-induced sulfate reduction at low temperature using organic carbon and methane as electron donors. Such kind of high-magnesium calcite that is rich in light carbon also indicates involvement of sulfate reducing bacteria. This work is supported by NASA Astrobiology Institute (N07-5489).

  11. Isolation, purification, crystallization and preliminary crystallographic studies of chitinase from tamarind (Tamarindus indica) seeds

    PubMed Central

    Patil, Dipak N.; Datta, Manali; Chaudhary, Anshul; Tomar, Shailly; Kumar Sharma, Ashwani; Kumar, Pravindra

    2009-01-01

    A protein with chitinase activity has been isolated and purified from tamarind (Tamarindus indica) seeds. 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 crystallized by the vapour-diffusion method using PEG 4000. The crystals 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

  12. Seeded Physical Vapor Transport of Cadmium-Zinc Telluride Crystals: Growth and Characterization

    NASA Technical Reports Server (NTRS)

    Palosz, W.; George, M. A.; Collins, E. E.; Chen, K.-T.; Zhang, Y.; Burger, A.

    1997-01-01

    Crystals of Cd(1-x)Zn(x)Te with x = 0.2 and 40 g in weight were grown on monocrystalline cadmium-zinc telluride seeds 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 crystals 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.

  13. Multi feed seed (MFS) high pressure crystallization of 1-2 in GaN

    NASA Astrophysics Data System (ADS)

    Bockowski, M.; Grzegory, I.; Lucznik, B.; Sochacki, T.; Nowak, G.; Sadovyi, B.; Strak, P.; Kamler, G.; Litwin-Staszewska, E.; Porowski, S.

    2012-07-01

    The growth and physical properties of GaN crystallized in a multi feed-seed (MFS) configuration by High Nitrogen Pressure Solution (HNPS) growth method are presented in detail. The conversion of free standing HVPE-GaN crystals to free standing HNPS-GaN is the basis of the MFS configuration. The influence of the experimental conditions (i.e. growth temperature, temperature gradient, etc.), the c-plane bowing of the initial substrate, the electrical properties of HNPS-GaN, and the rate and mode of growth from solution are analyzed. We show that the HNPS-GaN crystals have better structural quality than their HVPE-GaN seeds. The defect density decreases with increasing growth temperature, reaching 5×105 cm-2 for crystals grown at 1420 °C or higher. In contrast, the free carrier concentration in HNPS-GaN increases with increasing growth temperature, reaching 7×1019 cm-3 for samples crystallized at 1440 °C. Thus the possibility to obtain good quality plasmonic GaN substrates for laser diodes can be realized.

  14. Research paper Nanostructured calcite precipitated under hydrothermal conditions in the presence

    E-print Network

    Montes-Hernandez, German

    Research paper Nanostructured calcite precipitated under hydrothermal conditions in the presence-L-cystine Crystallographic incorporation into calcite Selenium Selenium is an important trace metalloid, whose global cycle associated with carbonate phases, with Se being gener- ally incorporated as an impurity in calcite crystals

  15. Crystal Structure of a 16 kDa Double-headed Bowman-Birk Trypsin Inhibitor from Barley Seeds at

    E-print Network

    Suh, Se Won

    Crystal Structure of a 16 kDa Double-headed Bowman- Birk Trypsin Inhibitor from Barley Seeds at 1 The Bowman-Birk trypsin inhibitor from barley seeds (BBBI) consists of 125 amino acid residues with two trypsin inhibitor; BBBI, barley Bowman-Birk trypsin inhibitor; BBI, Bowman-Birk protease inhibitor; BPT

  16. Seed crystals with improved properties for melt processing superconductors for practical applications

    DOEpatents

    Veal, Boyd W. (Downers Grove, IL); Paulikas, Arvydas (Downers Grove, IL); Balachandran, Uthamalingam (Hinsdale, IL); Zhong, Wei (Chicago, IL)

    1997-01-01

    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 crystal seed 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 crystal seed 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 crystal seed 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.

  17. Seed crystals with improved properties for melt processing superconductors for practical applications

    DOEpatents

    Veal, B.W.; Paulikas, A.; Balachandran, U.; Zhong, W.

    1997-03-18

    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 crystal seed 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 crystal seed 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 crystal seed 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}.

  18. Crystallization and initial crystallographic characterization of a vicilin-type seed storage protein from Pinus koraiensis

    SciTech Connect

    Jin, Tengchuan; Fu, Tong-Jen; Kothary, Mahendra H.; Howard, Andrew; Zhang, Yu-Zhu

    2007-12-01

    In this study, the Korean pine (Pinus koraiensis) vicilin-type 7S seed storage protein was isolated from defatted pine-nut extract and purified by sequential gel-filtration and anion-exchange chromatography. Well diffracting single crystals were obtained by the vapour-diffusion method in hanging drops. The cupin superfamily of proteins includes the 7S and 11S seed storage proteins. Many members of this family of proteins are known allergens. In this study, the Korean pine (Pinus koraiensis) vicilin-type 7S seed storage protein was isolated from defatted pine-nut extract and purified by sequential gel-filtration and anion-exchange chromatography. Well diffracting single crystals were obtained by the vapor-diffusion method in hanging drops. The crystals belong to the primitive cubic space group P2{sub 1}3, 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 Å{sup 3} Da{sup ?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.

  19. Crystallization and preliminary X-ray diffraction analysis of a lectin from Canavalia maritima seeds.

    PubMed

    Gadelha, Carlos Alberto de Almeida; 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 de; Cavada, Benildo S

    2005-01-01

    A lectin from Canavalia maritima seeds (ConM) was purified and submitted to crystallization experiments. The best crystals 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 A resolution using a synchrotron-radiation source. The ConM crystal belongs to the orthorhombic space group P2(1)2(1)2, with unit-cell parameters a = 67.15, b = 70.90, c = 97.37 A. 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. PMID:16508099

  20. Extracellular matrix protein in calcified endoskeleton: a potential additive for crystal growth and design

    NASA Astrophysics Data System (ADS)

    Azizur Rahman, M.; Fujimura, Hiroyuki; Shinjo, Ryuichi; Oomori, Tamotsu

    2011-06-01

    In this study, we demonstrate a key function of extracellular matrix proteins (ECMPs) on seed crystals, 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 crystallization. We previously studied with the ECMPs from a different type of soft coral ( Sinularia polydactyla) without introducing any seed crystals in the process , which showed different results. Thus, crystallization on the seed 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 crystallization was initiated in a supersaturated solution on seed particles of calcite (1 0 4) with and without ECMPs. No change in the crystal growth shape occurred without ECMPs present during the crystallization process. However, with ECMPs, the morphology and phase of the crystals in the crystallization process changed dramatically. Upon completion of crystallization with ECMPs, an attractive crystal morphology was found. Scanning electron microscopy (SEM) was utilized to observe the crystal morphologies on the seeds surface. The mineral phases of crystals nucleated by ECMPs on the seeds surface were examined by Raman spectroscopy. Although 50 mM Mg 2+ is influential in making aragonite in the crystallization process, the ECMPs significantly made calcite crystals even when 50 mM Mg 2+ was present in the process. Crystallization with the ECMP additive seems to be a technically attractive strategy to generate assembled micro crystals that could be used in crystals growth and design in the Pharmaceutical and biotechnology industries.

  1. Crystallization and preliminary X-ray diffraction analysis of a lectin from Canavalia maritima seeds

    SciTech Connect

    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.

    2005-01-01

    A lectin from C. maritima was crystallized using the vapour-diffusion method and crystals 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 seeds (ConM) was purified and submitted to crystallization experiments. The best crystals 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 crystal 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.

  2. Single-contact pressure solution creep on calcite monocrystals

    E-print Network

    Zubtsov, Sergei; Gratier, Jean-Pierre; Dysthe, Dag; Traskine, Vladimir

    2005-01-01

    Pressure solution creep rates and interface structures have been measured by two methods on calcite single crystals. In the first kind of experiments, calcite monocrystals were indented at 40 degrees C for six weeks using ceramic indenters under stresses in the 50-200 MPa range in a saturated solution of calcite and in a calcite-saturated aqueous solution of NH4Cl. The deformation (depth of the hole below the indenter) is measured ex-situ at the end of the experiment. In the second type of experiment, calcite monocrystals were indented by spherical glass indenters for 200 hours under stresses in the 0-100 MPa range at room temperature in a saturated aqueous solution of calcite. The displacement of the indenter was continuously recorded using a specially constructed differential dilatometer. The experiments conducted in a calcite-saturated aqueous solution of NH4Cl show an enhanced indentation rate owing to the fairly high solubility of calcite in this solution. In contrast, the experiments conducted in a calc...

  3. Characterization of physicochemical and thermal properties and crystallization behavior of krabok (Irvingia Malayana ) and rambutan seed fats.

    PubMed

    Sonwai, Sopark; Ponprachanuvut, Punnee

    2012-01-01

    Fatty acid composition, physicochemical and thermal properties and crystallization behavior of fats extracted from the seeds of krabok (Irvingia Malayana) and rambutan (Nephelium lappaceum L.) trees grown in Thailand were studied and compared with cocoa butter (CB). The krabok seed fat, KSF, consisted of 46.9% lauric and 40.3% myristic acids. It exhibited the highest saponification value and slip melting point but the lowest iodine values. The three fats displayed different crystallization behavior at 25°C. KSF crystallized into a mixture of ?' and pseudo-?' structures with a one-step crystallization curve and high solid fat content (SFC). The fat showed simple DSC crystallization and melting thermograms with one distinct peak. The rambutan seed fat, RSF, consisted of 42.5% arachidic and 33.1% oleic acids. Its crystallization behavior was more similar to CB than KSF, displaying a two-step crystallization curve with SFC lower than that of KSF. RSF solidified into a mixture of ?' and pseudo-?' before transforming to ? after 24 h. The large spherulitic microstructures were observed in both KSF and RSF. According to these results, the Thai KSF and RSF exhibited physicochemical, thermal characteristics and crystallization behavior that could be suitable for specific applications in several areas of the food, cosmetic and pharmaceutical industries. PMID:23196867

  4. Isotopic fractionation of cadmium into calcite

    NASA Astrophysics Data System (ADS)

    Horner, Tristan J.; Rickaby, Rosalind E. M.; Henderson, Gideon M.

    2011-12-01

    Cadmium mimics the distribution of the macronutrient phosphate in the oceans, and has uses as a palaeoproxy of past ocean circulation and nutrient utilization. Isotopic analyses of dissolved Cd in modern seawater show potential as a new tool for disentangling phytoplankton utilization of Cd from abiotic processes, such as ocean mixing. Extending this information into the past requires the Cd isotope signal to be captured and faithfully preserved in a suitable sedimentary archive. However, the role that environmental factors, such as temperature, may play in controlling Cd isotope fractionation into such archives has not been assessed. To this end, we have performed controlled inorganic CaCO 3 precipitation experiments in artificial seawater solutions. We grew calcite under different precipitation rates, temperatures, salinities, and ambient [Mg 2 + ], before measuring Cd isotopic compositions by double spike MC-ICPMS. We find that the isotopic fractionation factor for Cd into calcite ( ?-C) in seawater is always less than one (i.e. light isotopes of Cd are preferred in calcite). The fractionation factor has a value of 0.99955 ± 0.00012 and shows no response to temperature, [Mg 2 + ], or precipitation rate across the range studied. The constancy of this fractionation in seawater suggests that marine calcites may provide a record of the local seawater composition, without the need to correct for effects due to environmental variables. We also performed CaCO 3 growth in freshwater and, in contrast to calcite precipitated from artificial seawater solutions, no isotopic offset was recorded between the growth solution and calcite ( ?-Cd=1.0000±0.0001). Cadmium isotope fractionation during calcite growth can be explained by a kinetic isotope effect during the largely unidirectional incorporation of Cd at the mineral surface. Further, the rate of Cd uptake and isotopic fractionation can be modulated by increased ion blocking of crystal surface sites at high salinity. The fractionation of Cd isotopes observed during precipitation of calcite has the same direction and similar magnitude to that implicated for Cd removal from the surface ocean by seawater measurements. However, flux calculations show that CaCO 3 precipitation is unlikely to play a significant role in setting the Cd isotope composition in seawater, compared to Cd utilization in phytoplankton soft tissue. Marine carbonates therefore record seawater Cd isotope chemistry - with potential as a palaeoceanographic proxy - rather than drive oceanic Cd isotope compositions.

  5. Improving the diffraction of full-length human selenomethionyl metavinculin crystals by streak-seeding

    SciTech Connect

    Rangarajan, Erumbi S.; Izard, Tina

    2012-06-28

    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. Crystals 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-seeding markedly improved the stability, crystal-growth rate and diffraction quality of DCM-associated mutant metavinculin crystals, allowing complete data collection to 3.9 {angstrom} resolution. These crystals 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}.

  6. Interaction of alcohols with the calcite surface.

    PubMed

    Bovet, N; Yang, M; Javadi, M S; Stipp, S L S

    2015-02-01

    A clearer understanding of calcite 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 calcite where the individual crystals 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 calcite 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 calcite 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. PMID:25533590

  7. Seed

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cottonseed is a second product of the cotton plant that accounts for between 15 and 25% of the crop value. The seed is extracted for oil, producing meal, hulls, and linters as co-products, or it is used whole as a protein feed ingredient for ruminant animals. The oil fraction is the most valuable ...

  8. Purification, crystallization and preliminary X-ray characterization of a haemagglutinin from the seeds of Jatropha curcas.

    PubMed

    Nair, Divya N; Suresh, C G; Singh, Desh Deepak

    2011-12-01

    The plant Jatropha curcas (Euphorbiaceae) is an important source of biofuel from the inedible oil present in its toxic seeds. The toxicity arises from the presence of curcin, a ribosome-inactivating protein showing haemagglutination activity. In this communication, the purification, crystallization and preliminary X-ray characterization are reported of a small protein isolated from J. curcas seeds with a molecular mass of ~10 kDa that agglutinates rabbit erythrocytes. The protein was crystallized using the hanging-drop vapour-diffusion method and also by the microbatch method in 72-well HLA plates, using PEG 8000 as the precipitant in both conditions. X-ray diffraction data collected from the rod-shaped crystals were processed in the orthorhombic space group P2(1)2(1)2(1). The crystals diffracted to 2.8 Å resolution at 103 K. PMID:22139159

  9. Growth of organic molecular single crystal trans-stilbene by selective self seeding from vertical Bridgman technique

    NASA Astrophysics Data System (ADS)

    Arulchakkaravarthi, A.; Jayavel, P.; Santhanaraghavan, P.; Ramasamy, P.

    2002-01-01

    Single crystal growth of organic molecular materials by melt growth is plagued by serious difficulties owing to poor thermal conductivity, non-availability of good seed etc. Of all the melt growth techniques, Bridgman technique is widely preferred because of the low cost, versatility, easy adaptability, simple instrumentation etc. In the Bridgman technique the control on the formation/birth of the first single nuclei is still an art and in this paper we have proposed a selective self seeding technique for initiating single crystal growth. Trans-stilbene crystals have been grown using vertical Bridgman technique and using a modified ampoule design. Trans-stilbene crystal grown by using conventional method and by the present method were characterized for quality assessment by DCD and time resolution measurements.

  10. Influence of seed nano-crystals on electrical properties and phase transition behaviors of Ba0.85Sr0.15Ti0.90Zr0.10O3 ceramics prepared by seed-induced method

    NASA Astrophysics Data System (ADS)

    Sutjarittangtham, Krit; Intatha, Uraiwan; Eitssayeam, Sukum

    2015-05-01

    This work studied the effects of seed nano-crystal on the electrical properties and the phase transition behaviors of Ba0.85Sr0.15Ti0.90Zr0.10O3 (BSZT) ceramics. The BSZT ceramics were prepared by the seed-induced method. The seed nano-crystal were prepared by the molten salt technique, and NaCl-KCl (1:1 by mole) eutectic mixtures were used as the flux.[1] The ceramic powders were prepared by using a conventional method which added seed nano-crystals at various ratios. Results indicated that seed nano-crystals enhanced the electrical properties of ceramics. The sample with a 20 wt. % seed nano crystals has excellent value of dielectric constant ( µ r ) of 34698 at maximum temperature. The phase transition temperature was observed at 60°C. The morphology was found that the grain size increasing significantly with an increased of seed nano crystals. The relaxor ferroelectric phase transition behavior was shown by a diffuseness parameter ( ³). An increase in the BSZT-seed showed a decreased in ³ value from 1.61 to 1.44. Thus the ferroelectric of the BSZT ceramics can be confirmed by hysteresis loop.[Figure not available: see fulltext.

  11. Physicochemical characteristics of drip waters: Influence on mineralogy and crystal morphology of recent cave carbonate precipitates

    NASA Astrophysics Data System (ADS)

    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

    2014-11-01

    Speleothems are one of the most intensively explored continental archives for palaeoclimate variability. The parameters, however, that control speleothem petrography and its changes with time and space, specifically calcite crystal morphology and carbonate mineralogy, are still poorly understood. In order to shed light on processes and their products, precipitation experiments of recent carbonate crystals on watch glasses and glass plates were performed in seven selected caves. Drip water sites were analysed for their fluid Mg/Ca molar ratio, pH, degree of saturation for calcite and aragonite and drip rates. Corresponding precipitates were analysed with respect to their mineralogy, calcite crystal morphology and Mg/Ca molar ratio of calcite. The following results are found: High fluid Mg/Ca ratios are found only for caves situated in dolostone, thus the hostrock lithology indirectly controls the carbonate mineralogy and calcite crystal morphology of speleothems. The precipitation of aragonite in place of calcite occurred only in dolostone caves and is bound to very specific conditions. These are: high fluid Mg/Ca ratios (?0.5), high fluid pH (>8.2) and low fluid saturation indices for calcite (<0.8). These specific conditions are induced by slow drip rates of <0.2 ml/min as often under more arid conditions, causing the precipitation of calcite/aragonite prior to reaching the stalagmite top. Due to this, fluid chemistry is altered, which in turn leads to changes in carbonate mineralogy and geochemistry on the stalagmite top. Calcite growth is inhibited at high fluid Mg/Ca ratios and hence, aragonite precipitation is kinetically stabilised. An increase of the drip water Mg/Ca ratio leads to an increased incorporation of Mg2+ into the calcite crystal lattice and thus, to a change in calcite crystal morphology. Four distinctive changes occur with increasing Mg2+ incorporation: (i) development of new forms (steeper rhombohedra and base pinacoid) at the edges and corners of the crystal seed, (ii) crystal habit tend to elongate along [0 0 1] due to slower growth of faces with high Mg2+ densities, (iii) reconstitution of crystal faces with low Mg2+ densities, and (iv) occurrence of calcite crystals 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 calcite crystals. Based on the data shown here, the relation of Mg2+ incorporation and the resulting changes in calcite crystal morphologies as well as the conditions of aragonite precipitation are now clearly better understood. Further work should aim at linking the calcite crystal morphology of watch glass precipitates with calcite crystal fabrics in speleothems in order to exploit the petrographic archive of speleothem deposits.

  12. 1677 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com Brittlestar-Inspired Microlens Arrays Made of Calcite

    E-print Network

    Qi, Limin

    -Inspired Microlens Arrays Made of Calcite Single Crystals Xiaozhou Ye, Fei Zhang, Yurong Ma, and Limin Qi] As a typical linearly birefringent crystal, calcite has been widely used for control and charac- terization of the polarization states of light,[14,24,25] but the controllable fabrication of MLAs built from calcite single

  13. X-Ray Characterization of Structural Defects in Seeded and Self-Seeded ZnSe Crystal Grown by PVT in Horizontal and Vertical Configurations

    NASA Technical Reports Server (NTRS)

    Raghothamachar, B.; Dudley, M.; Su, C.-H.; Volz, H. M.; Matyi, R.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    As part of a pre-flight ground based investigation of crystal growth of II-VI compound semiconductors, a number of ZnSe boules have been grown by physical vapor transport (PVT) at Marshall Space Flight Center. Boules were grown in both horizontal and vertical configurations and seeded and self-seeded growth techniques were employed. As-grown and/or cleaved boules were examined by a combination of synchrotron white beam x-ray topography (SWBXT) and high resolution triple axis diffraction (HRTXD) to characterized the structural defects and correlate them with the growth conditions. Horizontal grown boules tend to grow away from the ampoule wall (contactless growth) and generally exhibit large (110) facets parallel to the gravity vector. Vertical grown boules grew to the full diameter of the ampoule and exhibited no faceting. X-ray topography combined with back reflection x-ray diffraction revealed the presence of lamellar twins (180 deg type about the [111] axis) in horizontal grown boules while vertically grown boules contain a few large grains, some of which are twinned. X-ray topographs and reciprocal space maps recorded from the boules show the better crystal quality of horizontal grown boules. The relationship between crystal quality and gravity vector is investigated. Further, an attempt is made to extend the Hurle theory of twin nucleation in Czochralski grown crystals to explain the twinning mechanisms in horizontal grown boules.

  14. The application of time-dependent ice crystal trajectory and growth model for the evaluation of cloud seeding experiment using liquid carbon dioxide

    NASA Astrophysics Data System (ADS)

    Nishiyama, K.; Wakimizu, K.; Maki, T.; Suzuki, Y.; Morita, O.; Tomine, K.

    2012-12-01

    This study evaluated the results of cloud seeding experiment conducted on 17th January, 2008, in western Kyushu, Japan, using simplified time-dependent ice crystal growth and trajectory cloud model, which is characterized by 1) depositional diffusion growth process only of an ice crystal, and 2) the pursuit of the growing ice crystal based on wind field and ice crystal terminal velocity. For the estimation of the ice crystal growth and trajectory, the model specifies ice supersaturation ratio that expresses the degree of competition growth among ice crystals formed by LC seeding for existing water vapor, assuming no effect of natural ice crystals. The model is based on ice crystal growth along a- and c-axes depending on air temperature and ice supersatuation, according to Chen and Lamb (1994). The cloud seeding experiment was conducted by applying homogeneous nucleation (rapid cooling of air mass and subsequent formation of many ice crystals~1013/g LC) of Liquid Carbon (LC) dioxide seeding 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 seeding 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 seeding experiment. In the next, the observed cloud seeding results were evaluated by estimating the trajectory of artificially-induced growing ice crystal. The results show that the trajectory of artificial ice crystals depends on the degree of completion growth mode. Free growth brings rapid growth of an ice crystal and, therefore, the ice crystal falls into lower layers for a short time. On the other hand, as the degree of competition is higher, ice crystal growth and falling are slower. The result (the right figure of Fig. 1) showed that the movement of observed isolated radar echo formed after LC cloud seeding is closely related to the trajectories of artificially-induced ice crystals depending on the specification of ice supersaturation. Therefore, it was found that time-dependent ice crystal growth and trajectory model is a useful tool for the evaluation of cloud seeding results regardless of its simplification and many uncertain factors. Fig.1 The left figure shows the movement of isolated radar echo formed by LC seeding. The right figure shows the comparison between observed radar echo location and estimated ice crystal location.

  15. Chemistry and petrography of calcite in the KTB pilot borehole, Bavarian Oberpfalz, Germany

    USGS Publications Warehouse

    Komor, S.C.

    1995-01-01

    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 calcite in the drilled section: 1) metamorphic calcite in calc-silicate and marble; 2) crack-filling calcite in all lithologies; and 3) replacement calcite in altered minerals. Crack-filling and replacement calcite postdate metamorphic calcite. Multiple calcite generations in individual cracks suggest that different generations of water repeatedly flowed through the same cracks. Crack-filling mineral assemblages that include calcite originally formed at temperatures of 150-350??C. Presently, crack-filling calcite 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 calcite to lower temperatures means that calcite chemistry tells us little about water-rock interactions in the crystal section of temperatures higher than ~120??C. -from Author

  16. Crystal structure of mature 2S albumin from Moringa oleifera seeds.

    PubMed

    Ullah, Anwar; Mariutti, Ricardo Barros; Masood, Rehana; Caruso, Icaro Putinhon; Gravatim Costa, Gustavo Henrique; Millena de Freita, Cristhyane; Santos, Camila Ramos; Zanphorlin, Leticia Maria; Rossini Mutton, Márcia Justino; Murakami, Mario Tyago; Arni, Raghuvir Krishnaswamy

    2015-12-01

    2S albumins, the seed 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 crystal structure of mMo-CBP3-1 determined at 1.7 Å resolution demonstrated that it is comprised of two proteolytically processed ?-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 crystal 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. PMID:26505799

  17. On the complex conductivity signatures of calcite precipitation

    SciTech Connect

    Wu, Yuxin; Hubbard, Susan; Williams, Kenneth Hurst; Ajo-Franklin, Jonathan

    2009-11-01

    Calcite 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 calcite 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 calcite precipitation. Calcite 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 calcite precipitation, with the precipitation volume and crystal size controlling the overall polarization magnitude and relaxation time constant. We attribute the observed responses to polarization at the electrical double layer surrounding calcite crystals. Our experiment illustrates the potential of electrical methods for characterizing the distribution and aggregation state of nonconductive minerals like calcite. 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).

  18. Characterization of Al2O3 coatings oxidized from Al with different proportion of seed crystals at a lower temperature

    NASA Astrophysics Data System (ADS)

    Wang, Chen; Lin, Yuebin; He, Fei; Luo, Xinyi; Tao, Jie

    2013-10-01

    Al layer with ?-Al2O3 seed crystals was prepared on the surface of 316L stainless steel (SS) by a double cathodes discharge technique, in which the mixed targets of pure Al doped with different proportions of ?-Al2O3 were used. Then, Al2O3 coatings were obtained after plasma oxidization at 580 °C. The phase composition, microstructure and morphology of the coatings were studied respectively by means of glancing-angle (1°) X-ray diffractometry (GAXRD) and scanning electron microscopy (SEM). Furthermore, the bonding force and corrosion resistance of the coatings were measured. The results indicated that ?-Al2O3 nucleated and grew surrounding the seed crystals as the Volmer-Weber Mode. The Al2O3 coating was compact, performing a good corrosion resistance and metallurgical bonding. The inducing effects of ?-Al2O3 with different fractions were discussed. ?-Al2O3 (5.5 wt.%) was distributed in the Al layer when the target possessing 10% ?-Al2O3 was used. After plasma oxidation, 65.54 wt.% ?-Al2O3 was obtained which was 10.34% more than that obtained by the oxidation of pure Al at the same condition. However, the inducing effects became weak with the further increment of content of ?-Al2O3 seed crystals.

  19. Human 17?-hydroxysteroid dehydrogenase-ligand complexes: crystals of different space groups with various cations and combined seeding and co-crystallization

    NASA Astrophysics Data System (ADS)

    Zhu, D.-W.; Han, Q.; Qiu, W.; Campbell, R. L.; Xie, B.-X.; Azzi, A.; Lin, S.-X.

    1999-01-01

    Human estrogenic 17?-hydroxysteroid dehydrogenase (17?-HSD1) is responsible for the synthesis of active estrogens that stimulate the proliferation of breast cancer cells. The enzyme has been crystallized using a Mg 2+/PEG (3500)/?-octyl glucoside system [Zhu et al., J. Mol. Biol. 234 (1993) 242]. The space group of these crystals is C2. Here we report that cations can affect 17?-HSD1 crystallization significantly. In the presence of Mn 2+ instead of Mg 2+, crystals 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 crystal 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 crystal packing in the presence of different cations. In order to further understand the structure-function relationship of 17?-HSD1, enzyme complexes with several ligands have been crystallized. As the steroids have very low aqueous solubility, we used a combined method of seeding and co-crystallization to obtain crystals of 17?-HSD1 complexed with various ligands. This method provides ideal conditions for growing complex crystals, with ligands such as 20?-hydroxysteroid progesterone, testosterone and 17?-methyl-estradiol-NADP +. Several complex structures have been determined with reliable electronic density of the bound ligands.

  20. Native crystal structure of a nitric oxide-releasing lectin from the seeds of Canavalia maritima.

    PubMed

    Gadelha, Carlos Alberto de Almeida; Moreno, Frederico Bruno Mendes Batista; Santi-Gadelha, Tatiane; Cajazeiras, João Batista; Rocha, Bruno Anderson Matias da; Assreuy, Ana Maria Sampaio; Lima Mota, Mário Rogério; Pinto, Nilson Vieira; Passos Meireles, Ana Vaneska; Borges, Júlio César; Freitas, Beatriz Tupinamba; Canduri, Fernanda; Souza, Emmanuel Prata; Delatorre, Plínio; Criddle, David Neil; de Azevedo, Walter Filgueira; Cavada, Benildo Sousa

    2005-12-01

    Here, we report the crystallographic study of a lectin from Canavalia maritima seeds (ConM) and its relaxant activity on vascular smooth muscle, to provide new insights into the understanding of structure/function relationships of this class of proteins. ConM was crystallized and its structure determined by standard molecular replacement techniques. The amino acid residues, previously suggested incorrectly by manual sequencing, have now been determined as I17, I53, S129, S134, G144, S164, P165, S187, V190, S169, T196, and S202. Analysis of the structure indicated a dimer in the asymmetric unit, two metal binding sites per monomer, and loops involved in the molecular oligomerization. These confer 98% similarity between ConM and other previously described lectins, derived from Canavalia ensiformis and Canavalia brasiliensis. Our functional data indicate that ConM exerts a concentration-dependent relaxant action on isolated aortic rings that probably occurs via an interaction with a specific lectin-binding site on the endothelium, resulting in a release of nitric oxide. PMID:16337811

  1. Biotic Control of Skeletal Growth by Scleractinian Corals in Aragonite–Calcite Seas

    PubMed Central

    Higuchi, Tomihiko; Fujimura, Hiroyuki; Yuyama, Ikuko; Harii, Saki; Agostini, Sylvain; Oomori, Tamotsu

    2014-01-01

    Modern scleractinian coral skeletons are commonly composed of aragonite, the orthorhombic form of CaCO3. Under certain conditions, modern corals produce calcite as a secondary precipitate to fill pore space. However, coral construction of primary skeletons from calcite has yet to be demonstrated. We report a calcitic 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 calcitic crystals in parts of the primary skeleton such as the septa; the deposits were observable under Raman microscopy. Using scanning electron microscopy, we observed different crystal morphologies of aragonite and calcite 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 crystal nucleation and growth processes. Our results indicate that the modern scleractinian coral Acropora mainly produces aragonite skeletons in both aragonite and calcite seas, but also has the ability to use calcite for part of its skeletal growth when incubated in calcite seas. PMID:24609012

  2. Thermodynamics of magnesian calcite solid-solutions at 25°C and 1 atm total pressure

    USGS Publications Warehouse

    Busenberg, Eurybiades; Plummer, L. Niel

    1989-01-01

    The stability of magnesian calcites was reexamined, and new results are presented for 28 natural inorganic, 12 biogenic, and 32 synthetic magnesian calcites. The magnesian calcite solid-solutions were separated into two groups on the basis of differences in stoichiometric solubility and other physical and chemical properties. Group I consists of solids of mainly metamorphic and hydrothermal origin, synthetic calcites prepared at high temperatures and pressures, and synthetic solids prepared at low temperature and very low calcite supersaturations () from artificial sea water or NaCl?MgCl2?CaCl2solutions. Group I solids are essentially binary s of CaCO2 and MgCO2, and are thought to be relatively free of structural defects. Group II solid-solutions are of either biogenic origin or are synthetic magnesian calcites and protodolomites (0–20 and ? 45 mole percent MgCO3) prepared at high calcite supersaturations () from NaCl?Na2SO4?MgCl2?CaCl2 or NaCl?MgCl2?CaCl2 solutions. Group II solid-solutions are treated as massively defective solids. The defects include substitution foreign ions (Na+ and SO42?) in the magnesian calcite lattice (point defects) and dislocations (~2 · 109 cm?2). Within each group, the excess free energy of mixing, GE, is described by the mixing model , where x is the mole fraction of the end-member Ca0.5Mg0.5CO3 in the solid-solution. The values of A0and A1 for Group I and II solids were evaluated at 25°C. The equilibrium constants of all the solids are closely described by the equation ln , where KC and KD are the equilibrium constants of calcite and Ca0.5Mg0.5CO3. Group I magnesian calcites were modeled as sub-regular solid-solutions between calcite and dolomite, and between calcite and “disordered dolomite”. Both models yield almost identical equilibrium constants for these magnesian calcites. The Group II magnesian calcites were modeled as sub-regular solid-solutions between defective calcite and protodolomite. Group I and II solid-solutions differ significantly in stability. The rate of crystal 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 calcites and the density of crystal defects. The literature on the occurrence and behavior of magnesian calcites in sea water and other aqueous solutions is also examined.

  3. Indiana is well known for its limestone, but did you know that limestone is made primarily of the mineral calcite (CaCO3)?

    E-print Network

    Polly, David

    of the mineral calcite (CaCO3)? Most people think of limestone as a nondescript, mostly gray rock, but the mineral calcite can have many different forms and colors. The minerals in limestone usually are tiny and not easily seen with the naked eye. When calcite forms visible crystals, they are often six-sided (hexagonal

  4. Time and metamorphic petrology: Calcite to aragonite experiments

    USGS Publications Warehouse

    Hacker, B.R.; Kirby, S.H.; Bohlen, S.R.

    1992-01-01

    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 calcite to aragonite transformation in polycrystalline marble are different from those for earlier experiments on powdered and single-crystal calcite. 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 calcite 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.

  5. Uranium Isotope Fractionation During Coprecipitation with Aragonite and Calcite

    NASA Astrophysics Data System (ADS)

    Chen, X.; Romaniello, S. J.; Herrmann, A. D.; Wasylenki, L. E.; Anbar, A. D.

    2014-12-01

    Natural variations in the 238U/235U ratio of marine carbonates may provide a useful way of constraining past variations in ocean redox conditions. However, before applying this novel redox proxy, it is essential to explore possible isotopic fractionation during U coprecipitation with aragonite and calcite. We investigated these effects in laboratory experiments. Aragonite and calcite coprecipitation experiments were conducted at pH 8.5±0.1 using a constant addition method [1]. More than 90% of the U was incorporated into the solid phase at the end of each experiment. Samples were purified using UTEVA chemistry and ?238/235U was measured using 233U-236U double-spike MC-ICP-MS with a precision of ±0.10‰ [2]. The aragonite experiment demonstrated a 238U/235U Rayleigh fractionation factor of ?=1.00008±0.00002 with the 238U preferentially incorporated. In contrast, the calcite experiment demonstrated no resolvable U isotope fractionation (?=1.00001±0.00003). To determine if U isotopes are affected during the early diagenetic conversion of aragonite to calcite, natural carbonate samples were collected along an aragonite-calcite transition across a single coral head in the Key Largo limestone, and characterized for U concentration and ?238/235U [3]. We found that the mean ?238/235U in aragonite (-0.33±0.07‰ 2se) was slightly heavier than that in calcite (-0.37±0.02‰ 2se). Further work is needed to address the mechanisms leading to differential isotopic fractionation of U(VI) during incorporation into aragonite and calcite. Possible drivers include differences in coordination in the crystal structure or equilibrium isotopic fractionation between various aqueous U(VI) species prior to incorporation. [1] Reeder et al. (2001) GCA 65, 3491-3503. [2] Weyer et al., (2008) GCA 72, 345-359. [3] Gill et al., (2008) GCA 72, 4699-4722.

  6. The calcite ? aragonite transformation in low-Mg marble: Equilibrium relations, transformations mechanisms, and rates

    USGS Publications Warehouse

    Hacker, Bradley R.; Rubie, David C.; Kirby, Stephen H.; Bohlen, Steven R.

    2005-01-01

    Experimental transformation of a rather pure natural calcite 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 calcite grains, producing Mg-rich calcite rods that persisted as relicts. Nucleation of aragonite occurred exclusively on grain boundaries, with aragonite [001] oriented subparallel to calcite [0001]. The aragonite crystals preferentially consumed the calcite crystal 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 calcite grains in between, stabilizing them and causing a few volume percent rodlike relicts of Mg-enriched calcite (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 calcite and dolomite.

  7. Enhancing mechanical properties of calcite by Mg substitutions: An ab initio study

    NASA Astrophysics Data System (ADS)

    Elstnerova, Pavlina; Friak, Martin; Hickel, Tilmann; Fabritius, Helge Otto; Lymperakis, Liverios; Petrov, Michal; Raabe, Dierk; Neugebauer, Joerg; Nikolov, Svetoslav; Zigler, Andreas; Hild, Sabine

    2011-03-01

    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 calcite. As the calcite 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 calcite. Our results show that substituting Ca by Mg causes an almost linear decrease in the crystal volume with Mg concentration and of substituted crystals. As a consequence the calcite crystals become stiffer giving rise e.g. to substantially increased bulk moduli.

  8. Fullerenol entrapment in calcite microspheres.

    PubMed

    Calvaresi, Matteo; Falini, Giuseppe; Bonacchi, Sara; Genovese, Damiano; Fermani, Simona; Montalti, Marco; Prodi, Luca; Zerbetto, Francesco

    2011-10-14

    Hybrid microspheres of calcium carbonate/fullerenol were synthesized and characterized. Their morphology depends on the concentration of the fullerenol solutions. XRD and FT-IR measurements proved that the mineral phase is consistently calcite, while fluorescence confocal microscopy indicated that fullerenol is homogenously included in the crystalline matrix. PMID:21881667

  9. Noncrystallographic calcite dendrites from hot-spring deposits at Lake Bogoria, Kenya

    SciTech Connect

    Jones, B.; Renaut, R.W.

    1995-01-02

    Complex calcite crystals 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 crystal splitting and spherulitic growth. Scandulitic (from Latin meaning shingle) dendrites are formed of stacked calcite crystals and are generally more compact than feather dendrites. These developed through the incremental stacking of rectangular-shaped calcite crystals that initially grew as skeletal crystals. 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 calcite crystal in these dendrites represents one episode of crystal growth. The orientation of the component crystals 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 crystal growth contributed to the formation of these unusual crystals.

  10. Purification, crystallization and preliminary crystallographic studies of a Kunitz-type proteinase inhibitor from tamarind (Tamarindus indica) seeds

    PubMed Central

    Patil, Dipak N.; Preeti; Chaudhry, Anshul; Sharma, Ashwani K.; Tomar, ­Shailly; Kumar, Pravindra

    2009-01-01

    A Kunitz-type proteinase inhibitor has been purified from tamarind (Tamarindus indica) seeds. 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 crystallized by the vapour-diffusion method using PEG 6000. The crystals 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

  11. Is calcite (1014) a chiral surface? Open Questions Is Calcite (1014) a Chiral Surface?

    E-print Network

    Kühnle, Angelika

    1014-01-01

    Is calcite (1014) a chiral surface? Open Questions Is Calcite (1014) a Chiral Surface? Philipp of the most stable calcite (1014) surface is achiral due to a glide plane symmetry,[14] the existence properties of the calcite (1014) surface, unambigu- ously concluding that the bulk-truncated surface

  12. Crystallization and preliminary X-ray diffraction analysis of a new chitin-binding protein from Parkia platycephala seeds

    SciTech Connect

    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

    2005-09-01

    Crystals 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 seeds and crystallized. Crystals 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 crystal 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.

  13. Design of a diamond-crystal monochromator for the LCLS hard x-ray self-seeding project

    NASA Astrophysics Data System (ADS)

    Shu, D.; Shvyd'ko, Y.; Amann, J.; Emma, P.; Stoupin, S.; Quintana, J.

    2013-03-01

    As the result of collaborations between the Advanced Photon Source (APS), Argonne National Laboratory, and the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory, we have designed and constructed a diamond crystal monochromator for the LCLS hard x-ray self-seeding project. The novel monochromator is ultrahigh-vacuum compatible to meet the LCLS linear accelerator vacuum environmental requirement. A special graphite holder was designed for strain-free mount of the 110-?m thin synthetic diamond crystal plate provided by Technological Institute for Super-hard and Novel Carbon Materials of Russia (TISNCM). An in-vacuum multi-axis precision positioning mechanism is designed to manipulate the thin-film diamond holder with resolutions and stabilities required by the hard x-ray self-seeding physics. Optical encoders, limit switches, and hardware stops are established in the mechanism to ensure system reliability and to meet the accelerator personal and equipment safety interlock requirements. Molybdenum shields are installed in the monochromator to protect the encoders and associated electronics from radiation damage. Mechanical specifications, designs, and preliminary test results of the diamond monochromator are presented in this paper.

  14. Barium recovery by crystallization in a fluidized-bed reactor: effects of pH, Ba/P molar ratio and seed.

    PubMed

    Su, Chia-Chi; Reano, Resmond L; Dalida, Maria Lourdes P; Lu, Ming-Chun

    2014-06-01

    The effects of process conditions, including upward velocity inside the column, the amount of added seed and seed 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 BaHPO? crystals 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 BaHPO? crystals with a size of around 0.84-1.0mm. The addition of seed crystals has no effect on barium removal. The use of a seed 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 crystals. The largest BaHPO? crystals 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 (Ba?(PO?)?) was obtained at pH 11. The compounds BaHPO? and BaO were present at a pH of below 10. PMID:24462085

  15. Nickel and manganese interaction with calcite

    SciTech Connect

    Doner, H; Zavarin, M

    1999-08-09

    Many divalent metal cations sorb to calcite surfaces and incorporate into calcite to varying degrees. Since calcite may sorb trace elements in the environment, the factors controlling metal-calcite interactions are critical to understanding element cycling. The interaction of divalent metal cations with calcite can be critical to toxic metal immobilization, nutrient cycling, interpretation of past redox conditions, tracing fluid flow, for example. Sorption of Ni and Mn on calcite surfaces was studied by Zachara et al.. At any particular pH, the sorption of Mn on calcite was greater than Ni. This was attributed in part to the similarity of divalent Mn and Ca with respect to ion size. Although direct spectroscopic evidence was not available, sorption/desorption results suggested that Mn quickly forms a surface precipitate or solid solution while Ni forms a hydrated surface complex that may incorporate into calcite much more slowly via recrystallization. Because Mn(II) ionic radius is similar to that of Ca(II) (0.80 versus 1.0{angstrom}), and because MnCO{sub 3} has a structure similar to calcite, it is likely that Mn can substitute directly for Ca in the calcite structure. The ionic radius of Ni(II) is significantly smaller (0.69{angstrom}) and Ni(OH){sub 2} precipitation is likely to be favored in most systems. For Ni, direct substitution for Ca is less likely or may require more significant calcite lattice deformation.

  16. Fabrication of a good-quality single grain YBCO sample through the control of seed crystals

    SciTech Connect

    Kim, C.J.; Hong, G.W.; Jee, Y.A.; Han, Y.H.; Han, S.C.; Sung, T.H.

    1999-09-01

    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-seeded melt processed YBCO samples. When a slab-like Sm-seed 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 seed 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.

  17. Microstructural control of calcite via incorporation of intracrystalline organic molecules in shells

    NASA Astrophysics Data System (ADS)

    Okumura, Taiga; Suzuki, Michio; Nagasawa, Hiromichi; Kogure, Toshihiro

    2013-10-01

    It is widely accepted that organic substances regulate or influence the structure of biominerals, but its direct evidences are not plenty. Here we show that the crystallographic microstructures in biotic calcites arise from incorporated intracrystalline organic molecules (IOMs), through a comparison between biotic calcites in shells and synthetic ones with the IOMs extracted from the shells. Although the prismatic layers of a pearl oyster (Pinctada fucata) and a pen shell (Atrina pectinata) morphologically resemble each other, the crystallographic features of constituent calcites are considerably different; in Pinctada, the IOMs are distributed inhomogeneously to form small-angle grain boundaries and associated crystal defects, whereas in Atrina, the IOMs are distributed almost homogeneously and defects are rare in the calcite crystals. We conducted in vitro calcite syntheses in the presence of the IOMs in EDTA-soluble extracts from the prisms. The IOMs in the extracts from Pinctada and Atrina were incorporated into synthetic calcites in a different manner, exhibiting defect-rich/free features as observed in the natural shells. With regard to amino acid compositions of the IOMs, the extract from Atrina has a higher proportion of acidic amino acids than that from Pinctada, implying that acidic proteins do not correlate directly to their affinity for calcium carbonate crystals.

  18. Crystallization and preliminary X-ray diffraction studies of frutalin, an ?-D-galactose-specific lectin from Artocarpus incisa seeds.

    PubMed

    Monteiro-Moreira, Ana Cristina de Oliveira; D'Muniz Pereira, Humberto; Vieira Neto, Antonio Eufrasio; Mendes Batista Moreno, Frederico Bruno; Duarte Pinto Lobo, Marina; Sousa, Felipe Domingos de; Moreira, Renato de Azevedo

    2015-10-01

    Frutalin is an ?-D-galactose-specific carbohydrate-binding glycoprotein with antitumour properties and is a powerful tool for tumour biomarker discovery. The crystallization and preliminary X-ray diffraction analysis of this lectin, which was isolated from Artocarpus incisa seeds, 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 crystals 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 crystals belonged to space group I2, with unit-cell parameters a = 76.17, b = 74.56, c = 118.98?Å, ? = 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. PMID:26457519

  19. Top-Seeded Solution Growth of Pb[(Zn1/3Nb2/3)0.93Ti0.07]O3 Single Crystals

    NASA Astrophysics Data System (ADS)

    Karaki, Tomoaki; Nakamoto, Maki; Adachi, Masatoshi

    2002-11-01

    Top-seeded solution growth (TSSG) of relaxor-based ferroelectric single crystal Pb[(Zn1/3Nb2/3)0.93Ti0.07]O3 (PZNT93/7) was investigated. PbO and PbO+B2O3 were used as fluxes. The solution compositions were (PZNT93/7)/PbO]=70/30 wt% and (PZNT93/7)/PbO/B2O3=70/29/1 wt%. A platinum stick, PZNT93/7 single crystal and Pb[(Mg1/3Nb2/3)0.65Ti0.35]O3 (PMNT65/35) single crystal were used as seeds. The addition of B2O3 was used to lower the growth temperature and reduce the rate of PbO evaporation. Crystals grown inside the melting solution had a pure perovskite structure and their Curie temperature was 168°C, corresponding to PZNT93/7 composition. However, it was found that the perovskite crystals decomposed little by little from the crystal surface to undesirable pyrochlore after being pulled out of the melt and exposed to air during the growth. Crystals grown at the melt surface were originally of pyrochlore structure. The investigated results revealed the possibility of growing these single crystals by a continually charged TSSG technique.

  20. In-Situ Partial Pressure Measurements and Visual Observation during Crystal Growth of ZnSe by Seeded Physical Vapor Transport

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Feth, Shari; Lehoczky, Sandor L.

    1999-01-01

    An in-situ monitoring furnace was constructed with side windows to perform partial pressure measurements by optical absorption and visual observation of the growing crystal. A fused silica -rowth ampoule with a 4.5 cm long square tube between the source and the seed was prepared for the optical absorption measurements. A ZnSe crystal was grown by the seeded 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 crystal was more Zn-rich than the source. The visual observation showed that the seed crystal first etched back, with greater thermal etching occurring along the edges of the seed crystal. Once the growth started, the crystal crew in a predominately contactless mode and facets were evident during growth. The crystal did not grow symmetrically which is believed to be due to the unintentional asymmetry of the radial thermal profile in the furnace.

  1. Crystallization and preliminary X-ray diffraction analysis of the lectin from Dioclea rostrata Benth seeds

    SciTech Connect

    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

    2006-02-01

    D. rostrata lectin was crystallized by hanging-drop vapor diffusion. The crystal 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 crystallized by hanging-drop vapour diffusion at 293 K. The crystal 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.

  2. Biaxially-Textured Photovoltaic Film Crystal Silicon on Ion Beam Assisted Deposition CaF2 Seed Layers on Glass

    SciTech Connect

    Groves, J. R.; Li, J. B.; Clemens, B. M.; LaSalvia, V.; Hasoon, F.; Branz, H. M.; Teplin, C. W.

    2012-05-01

    We grow biaxially textured heteroepitaxial crystal silicon (c-Si) films on display glass as a low-cost photovoltaic material. We first fabricate textured CaF{sub 2} seed layers using ion-beam assisted deposition, then coat the CaF{sub 2} with a thin, evaporated epitaxial Ge buffer and finally deposit heteroepitaxial silicon on the Ge. The silicon is grown by hot-wire chemical vapor deposition, a high-rate, scalable epitaxy technology. Electron and X-ray diffraction confirm the biaxial texture of the CaF{sub 2} and epitaxial growth of the subsequent layers. Transmission electron microscopy reveals columnar silicon grains about 500 nm across. We fabricate a proof-of-concept epitaxial film c-Si solar cell with an open circuit voltage of 375 mV that is limited by minority carrier lifetime.

  3. Seed Crystal Homogeneity Controls Lateral and Vertical Heteroepitaxy of Monolayer MoS2 and WS2.

    PubMed

    Yoo, Youngdong; Degregorio, Zachary P; Johns, James E

    2015-11-18

    Heteroepitaxy between transition-metal dichalcogenide (TMDC) monolayers can fabricate atomically thin semiconductor heterojunctions without interfacial contamination, which are essential for next-generation electronics and optoelectronics. Here we report a controllable two-step chemical vapor deposition (CVD) process for lateral and vertical heteroepitaxy between monolayer WS2 and MoS2 on a c-cut sapphire substrate. Lateral and vertical heteroepitaxy can be selectively achieved by carefully controlling the growth of MoS2 monolayers that are used as two-dimensional (2D) seed crystals. Using hydrogen as a carrier gas, we synthesize ultraclean MoS2 monolayers, which enable lateral heteroepitaxial growth of monolayer WS2 from the MoS2 edges to create atomically coherent and sharp in-plane WS2/MoS2 heterojunctions. When no hydrogen is used, we obtain MoS2 monolayers decorated with small particles along the edges, inducing vertical heteroepitaxial growth of monolayer WS2 on top of the MoS2 to form vertical WS2/MoS2 heterojunctions. Our lateral and vertical atomic layer heteroepitaxy steered by seed defect engineering opens up a new route toward atomically controlled fabrication of 2D heterojunction architectures. PMID:26488069

  4. Shock-induced devolatilization of calcite

    NASA Technical Reports Server (NTRS)

    Boslough, M. B.; Ahrens, T. J.; Vizgirda, J.; Becker, R. H.; Epstein, S.

    1982-01-01

    Experimental measurements of the release adiabats by Vizgirda (1981) indicate that substantial vaporization takes place upon release from shock pressures of 37 GPa for calcite and 14 GPa for aragonite. The present investigation includes the first controlled partial vaporization experiments on calcite. The experiments were conducted to test the predictions of the release adiabat experiments. The quantities of the gaseous species produced from shocked calcite 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 calcite 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 calcite to CO2 and CO. The devolatilization of calcite occurs at low pressure at significantly lower entropy densities than predicted on the basis of thermodynamic continuum models.

  5. Experimental investigation of surface energy and subcritical crack growth in calcite

    NASA Astrophysics Data System (ADS)

    RøYne, Anja; Bisschop, Jan; Dysthe, Dag Kristian

    2011-04-01

    Subcritical cracking behavior and surface energies are important factors in geological processes, as they control time-dependent brittle processes and the long-term stability of rocks. In this paper, we present experimental data on subcritical cracking in single calcite crystals exposed to glycol-water mixtures with varying water content. We find upper bounds for the surface energy of calcite that decrease with increasing water concentration and that are systematically lower than values obtained from molecular dynamics simulations. The relation of surface energy to water concentration can explain water weakening in chalks. The rate of subcritical crack growth in calcite is well described by a reaction rate model. The effect of increasing water on crack velocity is to lower the threshold energy release rate required for crack propagation. The slope of the crack velocity curve remains unaffected, something which strongly suggests that the mechanism for subcritical cracking in calcite does not depend on the water concentration.

  6. Effects of the method of apatite seed crystals addition on setting reaction of ?-tricalcium phosphate based apatite cement.

    PubMed

    Tsuru, Kanji; Ruslin; Maruta, Michito; Matsuya, Shigeki; Ishikawa, Kunio

    2015-10-01

    Appropriate setting time is an important parameter that determines the effectiveness of apatite cement (AC) for clinical application, given the issues of crystalline inflammatory response phenomena if AC fails to set. To this end, the present study analyzes the effects of the method of apatite seed crystals addition on the setting reaction of ?-tricalcium phosphate (?-TCP) based AC. Two ACs, both consisting of ?-TCP and calcium deficient hydroxyapatite (cdHAp), were analyzed in this study. In one AC, cdHAp was added externally to ?-TCP and this AC was abbreviated as AC(EA). In the other AC, ?-TCP was partially hydrolyzed to form cdHAp on the surface of ?-TCP. This AC was referred to as AC(PH). Results indicate a decrease in the setting time of both ACs with the addition of cdHAp. Among them, for the given amount of added cdHAp, AC(PH) showed relatively shorter setting time than AC(EA). Besides, the mechanical strength of the set AC(PH) was also higher than that of set AC(EA). These properties of AC(PH) were attributed to the predominant crystal growth of cdHAp in the vicinity of the ?-TCP particle surface. Accordingly, it can be concluded that the partial hydrolysis of ?-TCP may be a better approach to add low crystalline cdHAp onto ?-TCP based AC. PMID:26411440

  7. Stabilities of calcite and aragonite

    USGS Publications Warehouse

    Christ, C.L.; Hostetler, P.B.; Siebert, R.M.

    1974-01-01

    A revaluation of the 25° C activity-product constants of calcite (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 calcite 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.

  8. Solution composition-dependence of the Ca isotope composition of inorganic calcite

    NASA Astrophysics Data System (ADS)

    Gonzales, M. S.; Watkins, J. M.; Depaolo, D. J.

    2010-12-01

    Laboratory experiments have shown that the Ca isotope composition of calcite precipitated from aqueous solution may be sensitive to solution chemistry, temperature, and solution pH. Generally, inorganic calcite precipitation experiments yield calcite crystals that are enriched in the light isotope of Ca relative to the parent solution. Previous studies by Lemarchand et al. (2004) and Tang et al. (2008) showed that the Ca isotope composition (?44Ca) of calcite varies systematically with precipitation rate (R). The studies, however, obtained the opposite relationship between ?44Ca and R despite precipitating calcite at comparable pH, temperature, and Ca2+ as well as CO32- ion concentrations. There is evidence that Ca isotope variability in calcite reflects a mass dependence on reaction rate coefficients, but it is unknown if the mass dependence varies with solution chemistry. A potentially important difference between the studies is that Lemarchand et al. (2004) used parent solutions with higher ionic strength (0.85 versus 0.035). The purpose of this study is to determine the solution composition dependence, if any, on Ca isotope incorporation during calcite growth from aqueous solutions. For our experiments, a beaker containing 300 mL of CaCl2+NH4Cl solution was placed in a container filled with 1 atm of an N2+CO2 gas mixture. The degree of supersaturation with respect to calcite was controlled by the pCO2 of the gas, which was constantly replenished. As CO2 dissolved into solution, calcite crystals grew on the beaker walls. The pH of the solution was maintained by an autotitrator with NaOH as the titrant. Calcite precipitation rates are typically expressed in mmol/m2/hr, but this is difficult to quantify as the reactive surface area of the crystals is not controlled. Relative growth rates are determined by weighing the amount of calcite precipitated over the course of an entire experiment on a fixed surface area. This provides a first estimate of R and we are investigating methods for improving this aspect of the results. Experiments have yielded calcite crystals enriched in the light isotope of Ca relative to the parent solution by 0.4‰ to 1.6‰. Growth rates are estimated to range from 0.01 to 131 mmol/m2/hr, overlapping with the rates from Lemarchand et al. (2004) and Tang et al. (2008). In experiments where we use a solution with high ionic strength (0.7), we find that ?44Ca in calcite increases with increasing precipitation rate. This is in agreement with the findings of Lemarchand et al. (2004), although Ca isotopes are more fractionated in our experiments. We are exploring if a solution with lower ionic strength reproduces the results of Tang et al. (2008), in which ?44Ca in calcite decreased with increasing precipitation rate. Our hypothesis is that solution chemistry may play an important role in calcium isotope incorporation in calcite and we will present results using different parent solution compositions that explore this relationship. The ultimate goal is to understand the molecular scale controls on isotope separation at the mineral surface during crystal growth.

  9. Mechanism of Calcite Co-Orientation in the Sea Urchin Tooth

    SciTech Connect

    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.

    2009-12-01

    Sea urchin teeth are remarkable and complex calcite structures, continuously growing at the forming end and self-sharpening at the mature grinding tip. The calcite (CaCO{sub 3}) crystals of tooth components, plates, fibers, and a high-Mg polycrystalline matrix, have highly co-oriented crystallographic axes. This ability to co-orient calcite in a mineralized structure is shared by all echinoderms. However, the physico-chemical mechanism by which calcite crystals become co-oriented in echinoderms remains enigmatic. Here, we show differences in calcite 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 crystal 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.

  10. Heterogeneous growth of cadmium and cobalt carbonate phases at the (101¯4) calcite surface

    SciTech Connect

    Xu, Man; Ilton, Eugene S.; Engelhard, Mark H.; Qafoku, Odeta; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien N.

    2015-03-01

    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) calcite 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 calcite. Calcite single crystals were reacted in static conditions for 16 hours with CdCl2 and CoCl2 aqueous solutions with initial concentrations 0.3 ? [Cd2+]0 ? 100 ?M and 25 ? [Co2+]0 ? 200 ?M. The reacted crystals were imaged in situ with atomic force microscopy (AFM) and analyzed ex situ with X-ray photoelectron spectroscopy (XPS). AFM images of Cd-reacted crystals showed the formation of large islands elongated along the direction, clear evidence of heteroepitaxial growth, whereas surface precipitates on Co-reacted crystals were small round islands. Deformation of calcite 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 calcite substrate. In contrast, XPS measurements of the Co-reacted crystals 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 calcite 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.

  11. Structural Characterization of Lateral-grown 6H-SiC am-plane Seed Crystals by Hot Wall CVD Epitaxy

    NASA Technical Reports Server (NTRS)

    Goue, Ouloide Yannick; Raghothamachar, Balaji; Dudley, Michael; Trunek, Andrew J.; Neudeck, Philip G.; Woodworth, Andrew A.; Spry, David J.

    2014-01-01

    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 seed crystals (0.8mm x 0.5mm x 15mm) designed to replicate axially grown SiC single crystal fibers. The post-growth crystals 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 seed crystal. Axial and transverse sections from the as grown crystal 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 seed crystal 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 seed than in the grown crystal. Bundles of dislocations are observed propagating from the seed in m-axis lateral directions. Contrast extinction analysis of these dislocation lines reveals they are edge type basal plane dislocations that track the growth direction. Polytype phase transition and stacking faults were observed by high-resolution TEM (HRTEM), in agreement with SWBXT and Raman scattering.

  12. Nucleation, growth and evolution of calcium phosphate films on calcite.

    PubMed

    Naidu, Sonia; Scherer, George W

    2014-12-01

    Marble, a stone composed of the mineral calcite, 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 crystal and lattice compatibility with calcite. 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 calcite 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. PMID:25233226

  13. On-line near infrared spectroscopy as a Process Analytical Technology (PAT) tool to control an industrial seeded API crystallization.

    PubMed

    Schaefer, C; Lecomte, C; Clicq, D; Merschaert, A; Norrant, E; Fotiadu, F

    2013-09-01

    The final step of an active pharmaceutical ingredient (API) manufacturing synthesis process consists of a crystallization during which the API and residual solvent contents have to be quantified precisely in order to reach a predefined seeding 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 seeding of an API crystallization at industrial scale. Furthermore, the successful scale-up of the method proved its capability to be implemented in the manufacturing plant with the launch of the new API process. PMID:23764657

  14. Project Explorer: Get Away Special #007. [alloy solidification, seed germination, crystal growth, and radio transmission of payload data

    NASA Technical Reports Server (NTRS)

    Henderson, A. J., Jr.

    1984-01-01

    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 seeds, and the growth of potassium-tetracyanoplatinate hydrate crystals 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.

  15. Coprecipitation of Chromate with Calcite: Batch Experiments and X-ray Absorption Spectroscopy

    SciTech Connect

    Tang,Y.; Elzinga, E.; Lee, Y.; Reeder, R.

    2007-01-01

    Batch experiments, combined with in situ spectroscopic methods, are used to examine the coprecipitation of Cr(VI) with calcite, including partitioning behavior, site-specific distribution of Cr on the surface of calcite single crystals, and local coordination of Cr(VI) in the calcite structure. It is found that the concentration of Cr incorporated in calcite 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 calcite single crystals 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 calcite. Consideration of possible local coordination indicates that significant distortion or disruption is required to accommodate CrO{sub 4}{sup 2-}in the calcite structure.

  16. Hydrothermal replacement of calcite by Mg-carbonates

    NASA Astrophysics Data System (ADS)

    Jonas, Laura; Mueller, Thomas; Dohmen, Ralf

    2014-05-01

    The transport of heat and mass through the Earth's crust is coupled to mineral reactions and the exchange of isotopes and elements between different phases. Carbonate minerals are a major constituent of the Earth's crust and play an important role in different physical, chemical and even biological processes. In this experimental study, the element exchange reaction between calcite (CaCO3) and a Mg-rich fluid phase is investigated under hydrothermal conditions. Single crystals of calcite (2x2x2 mm) react with 1 ml of a 1 M MgCl2 solution at 200° C in a Teflon-lined steel autoclave for different times between one day and four weeks. The reaction leads to the formation of a porous reaction front and the pseudomorphic replacement of calcite by dolomite [CaMg(CO3)2] and magnesite (MgCO3). Scanning electron microscopy revealed that the reaction rim consists of small Mg-carbonate rhombs closely attached to each other, suggesting that the replacement reaction takes place by a dissolution-precipitation mechanism. Typically, the observed reaction front can be divided into two different domains. The outer part of the reaction rim, i.e. from the mineral surface in contact to the fluid inwards, consists of magnesite, whereas the inner part of the rim surrounding the unreacted calcite core consists of Ca-rich dolomite. The formation of a porous microstructure that varies in different parts of the reaction rim is a direct result of the large molar volume change induced by the replacement of calcite by magnesite and dolomite. The developing porosity therefore creates fluid pathways that promote the progress of the reaction front towards the unreacted core of the single crystal. Compositional profiles measured perpendicular to the mineral surface across the reactions rims using electron microprobe (EMPA) further revealed a compositional gradient within the reaction rim with regard to the structure-forming elements Mg and Ca. Here, the amount of Mg incorporated in both product phases increases with increasing distance from the unreacted calcite core, countered by a decrease of Ca incorporated. Both the coexistence of two different product phases and the distinct compositional gradient within the forming reaction rim are unequivocal signs of a chemical zonation of Ca and Mg in the fluid phase which mediates the element exchange between the reaction interface and the bulk solution. Atomic adsorption spectroscopy revealed that the Ca/Mg ratio in the reacted fluid increases as a function of time, reflecting the progressive exchange of Mg and Ca between the fluid and the solid phase. The time-dependence of the evolving Ca/Mg ratio can be fitted with a square root of time relation that indicates a transport controlled reaction. We interpret the hydrothermal replacement of calcite to operate via a dissolution/re-precipitation mechanism, whereas the reaction progress is controlled by the transport of the structure forming elements through the developing reaction rim.

  17. Do organic ligands affect calcite dissolution rates?

    NASA Astrophysics Data System (ADS)

    Oelkers, Eric H.; Golubev, Sergey V.; Pokrovsky, Oleg S.; Bénézeth, Pascale

    2011-04-01

    Steady state Iceland-spar calcite 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 calcite 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 calcite dissolution rates by as much as a factor of 35 and 500, respectively, compared to rates in organic anion-free solutions. Further calcite 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 calcite 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 calcite forward dissolution rates in most natural environments. Some effect on calcite reactivity may be observed, however, by the presence of organic anions if they change substantially the chemical affinity of the fluid with respect to calcite.

  18. Nickel adsorption on chalk and calcite

    NASA Astrophysics Data System (ADS)

    Belova, D. A.; Lakshtanov, L. Z.; Carneiro, J. F.; Stipp, S. L. S.

    2014-12-01

    Nickel uptake from solution by two types of chalk and calcite was investigated in batch sorption studies. The goal was to understand the difference in sorption behavior between synthetic and biogenic calcite. Experiments at atmospheric partial pressure of CO2, in solutions equilibrated with calcite and chalk and pH ranging from 7.7 to 8.8, explored the influence of initial concentration and the amount and type of sorbent on Ni uptake. Adsorption increases with increased surface area and pH. A surface complexation model describes the data well. Stability constants for the Ni surface complex are log KNi = - 1.12 on calcite and log KNi = - 0.43 and - 0.50 on the two chalk samples. The study confirms that synthetic calcite and chalk both take up nickel, but Ni binds more strongly on the biogenic calcite than on inorganically precipitated, synthetic powder, because of the presence of trace amounts of polysaccharides and clay nanoparticles on the chalk surface.

  19. Upscaling Calcite Growth Rates From the Mesoscale to the Macroscale

    SciTech Connect

    Bracco, Jacquelyn N; Stack, Andrew G; Steefel, Carl I

    2013-01-01

    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 calcite 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 calcite 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 seed material to SI 1.0 to generate/develop growth hillocks, or other factors.

  20. The Crystal Hotel: A Microfluidic Approach to Biomimetic Crystallization.

    PubMed

    Gong, Xiuqing; Wang, Yun-Wei; Ihli, Johannes; Kim, Yi-Yeoun; Li, Shunbo; Walshaw, Richard; Chen, Li; Meldrum, Fiona C

    2015-12-01

    A "crystal hotel" microfluidic device that allows crystal growth in confined volumes to be studied in situ is used to produce large calcite single crystals 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 crystals. PMID:26479157

  1. Ages and Origins of Calcite and Opal in the Exploratory Studies Facility Tunnel, Yucca Mountain, Nevada

    USGS Publications Warehouse

    Paces, James B.; Neymark, Leonid A.; Marshall, Brian D.; Whelan, Joseph F.; Peterman, Zell E.

    2001-01-01

    Deposits of calcite 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 calcite 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 crystal 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 crystal 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 calcite 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. Calcite 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) calcite tends to have the largest delta carbon-13 values and smallest delta oxygen-18 values compared to calcite from intermediate and outer positions. Basal calcite has relatively small strontium-87/strontium-86 ratios, between 0.7105 and 0.7120, that are similar to the initial isotopic compositions of the strontium-rich tuff units, whereas outer calcite has more radiogenic strontium-87/strontium-86 ratios between 0.7115 and 0.7127. Isotopic compositions of strontium, oxygen, and carbon in the outer (youngest) unsaturated-zone calcite are coincident with those measured in Yucca Mountain calcrete, which formed by pedogenic processes. The physical and isotopic data from calcite and opal indicate that they formed from solutions of meteoric origin percolating through a limited network of connected fracture pathways in the unsaturated zone rather than by inundation from ascending ground water originating in the saturated zone. Mineral assemblages, textures, and distributions within the unsaturated zone are distinctly different from those deposited below the water table at Yucca Mountain. The calcite and opal typically are present only on footwall surfaces of a small fraction of fractures and only on floors of a small fraction of lithophysal cavities. The similarities in the carbon, oxygen, and strontium isotopic compositions between fracture calcite and soil-zone calcite, as well as the gradation of textures from detritus-rich micrite in the soil to detritus-free spar 10 to 30 meters below the surface, also support a genetic link between the two depositional environments. Older deposits contain oxygen isotope compositions that indicate elevated temperatures of mineral formation during the early stages of deposition; however, in the youngest deposits these values are consistent with deposition under geothermal gradients similar to modern conditions. Correlations between mineral ages and varying Pleistocene climate conditions are not apparent from the current data. Cumulative evidence from calcite and opal deposits indicate

  2. Calcite dissolution in two deep eutrophic lakes

    SciTech Connect

    Ramisch, F.; Dittrich, M.; Mattenberger, C.; Wehrli, B.; Wueest, A.

    1999-10-01

    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 calcite 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 calcite 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 calcite 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 calcite 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 calcite precipitation in Sempachersee and Lago di Lugano, respectively. However, 61% of the precipitated calcite 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 calcite retention in sediments of hard water lakes.

  3. Radiaxial-fibrous calcites: A new look at an old problem

    NASA Astrophysics Data System (ADS)

    Richter, D. K.; Neuser, R. D.; Schreuer, J.; Gies, H.; Immenhauser, A.

    2011-07-01

    Marine radiaxial-fibrous and fascicular-optic calcites are very common but poorly understood pore-filling cements in Paleozoic and Mesozoic marine neritic and upper bathyal limestones. The main diagnostic feature of these cements is their converging or diverging crystal c-axis, respectively. The reasons for this anomalous texture are at present unknown. Another controversy is due to the relative lack of occurrences in Cenozoic strata and their apparent absence in Quaternary marine limestones. Despite these uncertainties, marine fibrous cements are thought by some to be amongst the best proxies for the geochemistry of ancient oceans because of the absence of metabolic effects during their precipitation. Applying electron backscatter diffraction analysis, we here for the first time document radiaxial-fibrous and subordinate fascicular-optic fibrous biominerals from well-preserved Jurassic and Cretaceous low-Mg calcite belemnite rostra. The finding of fibrous biogenic calcites in combination with the recent description of Holocene and modern fibrous calcites in stalagmites represents—in the view of the authors—a significant advance in carbonate research. Here, these findings are placed in their wider, processes-oriented context and the significance of biogenic and speloan fibrous calcite for their marine counterparts is assessed. Comparing the physico-chemical and organomineralic properties of different precipitation sites indicates that the diagnostic variations in the crystal c-axis orientation are not related to a specific nucleation environment or substratum. In contrast, preliminary crystallographic analyses suggest that kinetic factors during nucleation or subtle gradients in the statistical replacements of Ca 2+ by Mg 2+ in the crystal structure may lead to local strain resulting in converging or diverging crystal c-axes.

  4. Experimental and theoretical study of red-shifted solitonic resonant radiation in photonic crystal fibers and generation of radiation seeded Raman soliton

    NASA Astrophysics Data System (ADS)

    Bose, S.; Roy, S.; Chattopadhyay, R.; Pal, M.; Bhadra, S. K.

    2015-10-01

    Redshifted solitonic resonant radiation (RR) is a fascinating phase-matching phenomenon that occurs when an optical pulse, launched in the normal dispersion regime of photonic crystal fiber, radiates across the zero-dispersion point. The formation of such phase-matched radiation is independent of the generation of any optical soliton and mainly governed by the leading edge of an input pump which forms a shock front. The radiation is generated at the anomalous dispersion regime and found to be confined both in the time and frequency domain. We experimentally investigate the formation of such radiation in fabricated photonic crystal fiber for two different pulse width regimes (femtosecond and picosecond) with detailed theoretical analyses. Theoretically predicted results corroborate well with experimental results and confirm the existence of such unique radiation which is robust in nature. Further, we extend the study to long-length fiber and investigate the interplay between redshifted solitonic RR and intrapulse Raman scattering (IPRS). The consequence of the formation of such solitonic RR in an anomalous dispersion domain is found to be very interesting where it seeds a series of Raman solitons and behaves like a secondary source. These Raman solitons are now continuously redshifted and open up the possibility of wideband supercontinuum generation even in normal dispersion pumping. We fabricate a suitable photonic crystal fiber and experimentally demonstrate the RR-seeded IPRS process.

  5. Selective adsorption of L- and D-amino acids on calcite: Implications for biochemical homochirality

    NASA Technical Reports Server (NTRS)

    Hazen, R. M.; Filley, T. R.; Goodfriend, G. A.

    2001-01-01

    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. Crystals of the common rock-forming mineral calcite (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 crystal-growth surfaces. This selective adsorption is greater on crystals 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 calcite, with subsequent condensation polymerization, represents a plausible geochemical mechanism for the production of homochiral polypeptides on the prebiotic Earth.

  6. Stable isotopes in pedogenic calcite: Can the positive linear covariant trends be used to quantify paleo-evaporation rates?

    NASA Astrophysics Data System (ADS)

    Gröcke, D.; Ufnar, D.; Beddows, P. A.

    2007-12-01

    Paleoclimatological models suggest enhanced evaporation rates in subtropical regions during greenhouse- world conditions. Laboratory evaporation experiments show that calcites precipitated from variably saturated solutions yield a positive linear covariant trend (PLCT) in ?18O vs ?13C values. This investigation experimentally quantifies calcite PLCT so that ?13C of subtropical paleosol calcretes may be used as a regional proxy of paleo-evaporation rates. A series of powdered CaCO3 samples with ?18O and ?13C values of -19.6‰ and -37.2‰ VPDB respectively were dissolved in deionized water in a pressure sealed container; it also contained separate vials of calcite reacted with HCl to generate a range of pCO2 environments, thus simulating a soil atmosphere. The variable pCO2 conditions simulate expected soil atmosphere pCO2 conditions in a calcrete horizon during alternative phases of calcite dissolution and precipitation. After 24 hrs, the solutions were placed in an open beaker in an incubator at 36°C and allowed to evaporate. Aliquots of 100 ?L were removed at 24 hr intervals and the time of calcite crystal nucleation was also noted. Water analyses yielded ?18O enrichments ranging from an initial value of -4.8‰ VSMOW to a range of +10.0‰ to +14.8‰ VSMOW after an evaporation period of 75 hrs. The most enriched water values were attained from the solutions formed under lower pCO2 conditions (more enriched calcite ?18O, ?13C). The array of calcite ?18O vs ?13C values fall upon a PLCT that projects from a theoretical meteoric calcite line (MCL) calculated from the incubation temperature and deionized water ?18O and ?13C values. The precipitated calcite ?18O values range from the MCL value of -8.8‰ VPDB to +0.5‰ VPDB. The higher pCO2 waters precipitated calcite very early during evaporation, and thus the ?18O and ?13C calcite values are slightly enriched relative to the theoretical MCL. The lower pCO2 conditions precipitated calcite late in the evaporation of the fluids, and thus yield more enriched calcite ?18O and ?13C values. Ongoing experiments under warmer and cooler evaporation temperatures will aid in the development of a quantitative model for paleo-evaporation rates from paleosol calcretes.

  7. Experimental and theoretical study of red-shifted solitonic resonant radiation in photonic crystal fibers and generation of radiation seeded Raman solitons

    E-print Network

    Bose, Surajit; Chattopadhyay, Rik; Pal, Mrinmay; Bhadra, Shyamal K

    2015-01-01

    The red shifted solitonic resonant radiation is a fascinating phase matching phenomenon that occurs when an optical pulse, launched in the normal dispersion regime of photonic crystal fiber, radiates across the zero dispersion wavelength. The formation of such phase-matched radiation is independent of the generation of any optical soliton and mainly governed by the leading edge of input pump which forms a shock front. The radiation is generated at the anomalous dispersion regime and found to be confined both in time and frequency domain. We experimentally investigate the formation of such radiations in photonic crystal fibers with detailed theoretical analysis. Our theoretical predictions corroborate well with experimental results. Further we extend our study for long length fiber and investigate the interplay between red-shifted solitonic resonant radiation and intrapulse Raman scattering (IPRS). It is observed that series of radiation-seeded Raman solitons are generated in anomalous dispersion regime.

  8. Inhibition of calcite precipitation by natural organic material: Kinetics, mechanism, and thermodynamics

    USGS Publications Warehouse

    Lin, Y.-P.; Singer, P.C.; Aiken, G.R.

    2005-01-01

    The inhibition of calcite precipitation by natural organic material (NOM) in solutions seeded with calcite 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 calcite 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 calcite precipitation was dictated by the balance between the enthalpy change and the entropy change of the adsorption reaction. ?? 2005 American Chemical Society.

  9. The puzzling presence of calcite in skeletons of modern solitary corals from the Mediterranean Sea

    NASA Astrophysics Data System (ADS)

    Goffredo, Stefano; Caroselli, Erik; Mezzo, Francesco; Laiolo, Leonardo; Vergni, Patrizia; Pasquini, Luca; Levy, Oren; Zaccanti, Francesco; Tribollet, Aline; Dubinsky, Zvy; Falini, Giuseppe

    2012-05-01

    The skeleton of scleractinian corals is commonly believed to be composed entirely of aragonite due to the current Mg/Ca molar ratio of seawater, which thermodynamically favours the deposition of this polymorph of calcium carbonate (CaCO3). However, some studies have shown that other forms of CaCO3 such as calcite can be present in significant amount (1-20%) inside tropical coral skeletons, significantly impacting paleo-reconstructions of SST or other environmental parameters based on geochemical proxies. This study aims at investigating for the first time, (1) the skeletal composition of two Mediterranean solitary corals, the azooxanthellate Leptopsammia pruvoti and the zooxanthellate Balanophyllia europaea, across their life cycle, (2) the distribution of the different CaCO3 forms inside skeletons, and (3) their implications in paleoclimatology. The origin of the different forms of CaCO3 observed inside studied coral skeletons and their relationships with the species' habitat and ecological strategies are also discussed. CaCO3 composition of L. pruvoti and B. europaea was investigated at six sites located along the Italian coasts. Skeleton composition was studied by means of X-ray powder diffraction and Fourier transform infrared spectroscopy. A significant amount of calcite (1-23%) was found in more than 90% of the studied coral skeletons, in addition to aragonite. This calcite was preferentially located in the basal and intermediate areas than at the oral pole of coral skeletons. Calcite was also mainly located in the epitheca that covered the exposed parts of the coral in its aboral region. Interestingly in B. europaea, the calcite content was negatively correlated with skeleton size (age). The presence of calcite in scleractinian corals may result from different mechanisms: (1) corals may biologically precipitate calcite crystals at their early stages in order to insure their settlement on the substrate of fixation, especially in surgy environments; (2) calcite presence may result from skeletons of other calcifying organisms such as crustose coralline algae; and/or (3) calcite may result from the infilling of galleries of boring microorganisms which are known to colonize coral skeletons. We suggest that more than one of the above mentioned processes are involved.

  10. Isotopic tracer evidence for the amorphous calcium carbonate to calcite transformation by dissolution-reprecipitation

    NASA Astrophysics Data System (ADS)

    Giuffre, Anthony J.; Gagnon, Alexander C.; De Yoreo, James J.; Dove, Patricia M.

    2015-09-01

    Observations that some biogenic and sedimentary calcites grow from amorphous calcium carbonate (ACC) raise the question of how this mineralization process influences composition. However, the detailed pathway and geochemical consequences of the ACC to calcite transformation are not well constrained. This experimental study investigated the formation of calcite from ACC by using magnesium and calcium stable isotope labeling to directly probe the transformation pathway and controls on composition. Four processes were considered: dissolution-reprecipitation, solid state transformation, and combinations of these end-members. To distinguish between these scenarios, ACC was synthesized from natural isotope abundance solutions and subsequently transferred to spiked solutions that were enriched in 43Ca and 25Mg for the transformation to calcite. Isotope measurements by NanoSIMS determined the 43Ca/40Ca, and 25Mg/24Mg ratios of the resulting calcite crystals. Analysis of the data shows the transformation is best explained by a dissolution-reprecipitation process. We find that when a small amount of ACC is transferred, the isotopic signals in the resulting calcite are largely replaced by the composition of the surrounding spiked solution. When larger amounts of ACC are transferred, calcite compositions reflect a mixture between the ACC and initial solution end-member. Comparisons of the measurements to the predictions of a simple mixing model indicate that calcite compositions (1) are sensitive to relative amounts of ACC and the surrounding solution reservoir and (2) are primarily governed by the conditions at the time of ACC transformation rather than the initial ACC formation. Shifts in calcite composition over the duration of the transformation period reflect the progressive evolution of the local solution conditions. This dependence indicates the extent to which there is water available would change the end point composition on the mixing line. While these findings have significant geochemical implications, the question remains whether this transformation pathway is generally followed when biomineralization involves ACC or is particular to these inorganic experiments. Insights from this study nonetheless suggest that some types of compositional variability, such as 'vital effects', may be explained in-part by a co-evolution of reservoir and products over the duration of the transformation.

  11. Fluid inclusion studies of calcite veins from Yucca Mountain, Nevada, Tuffs: Environment of formation

    SciTech Connect

    Roedder, E.; Whelan, J.F.; Vaniman, D.T.

    1994-12-31

    Calcite 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 calcite crystallized from fluids at <100{degrees}C. The vapor-filled inclusions provide evidence that a separate vapor phase was present in the fluid during crystallization. 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 calcite crystals 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 crystal surface.

  12. Controls on trace-element partitioning in cave-analogue calcite

    NASA Astrophysics Data System (ADS)

    Day, Christopher C.; Henderson, Gideon M.

    2013-11-01

    We report trace-element data from a series of carbonate growth experiments in cave-analogue conditions in the laboratory with the goal of better understanding environmental controls on trace-element incorporation in stalagmites. The experimental setup closely mimics natural processes (e.g. precipitation driven by CO2-degassing, low ionic strength solution, thin solution-film) but with a tight control on growth conditions (temperature, pCO2, drip rate, calcite saturation index and the composition of the initial solution). Calcite is dissolved in deionized water in a 20,000 ppmV pCO2 environment, with trace-elements (Li, Na, Mg, Co, Sr, Cd, Ba, U) at appropriate concentrations to mimic natural cave drip-waters. This solution is dripped onto glass plates (coated with seed-calcite) in a lower pCO2 environment at 7, 15, 25 and 35 °C and drip rates of 2, 6 and 10 drips per minute. D(Sr) was shown to be statistically invariant over the full range of temperature and growth rate studied. No relationship between Sr/Ca and growth rate is therefore expected in stalagmite samples over comparable growth rates. D(Mg) has a relationship with temperature defined by D(Mg) = 0.01e0.02[±0.006]T, but temperature is not expected to be the dominant control on Mg/Ca in cave calcite due to the larger impact of calcite precipitation on Mg/Ca. Over short timescales, in conditions where temperature is well buffered, the fraction of calcium remaining in solution (f) is likely to be the dominant control on Mg/Ca and other trace-element ratios. But differences in the response of trace-elements to f and T may allow their combined use to assess past cave conditions. High Cd/Castalagmite is particularly indicative of low amounts of prior calcite precipitation and Cd/Ca would be a useful addition to trace-element studies of natural stalagmites. Significant scatter is observed in trace-element ratios during the laboratory experiments, which cannot be explained by simple Rayleigh distillation. This scatter is well explained by solution mixing and by the mixing of calcite with different fractions of calcite growth. Accounting for the effects of mixing on trace-element concentrations or ratios may help to achieve more robust interpretations of stalagmite chemistry as part of a multi-proxy approach to assessment of past environments.

  13. Calcite Reaction Kinetics in Saline Waters 

    E-print Network

    Finneran, David

    2012-02-14

    The effect of ionic strength (I), pCO2, and temperature on the reaction kinetics of calcite was investigated in magnesium-free, phosphate-free, low calcium (mCa^2 ? 0.01 – 0.02 molal) simple KCl and NaCl solutions from both undersaturated...

  14. Cyclic Cratonic Carbonates and Phanerozoic Calcite Seas.

    ERIC Educational Resources Information Center

    Wilkinson, Bruce H.

    1982-01-01

    Discusses causes of cyclicity in cratonic carbonate sequences and evidence for and potential significance of postulated primary calcite 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…

  15. Shock-induced effects in calcite from Cactus Crater

    NASA Technical Reports Server (NTRS)

    Vizgirda, J.; Ahrens, T. J.; Tsay, F.-D.

    1980-01-01

    The paper discusses shock metamorphism of calcite 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 crystal 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.

  16. Understanding control of calcitic biomineralization-proteomics to the rescue.

    PubMed

    Hincke, Maxwell T

    2013-12-01

    The avian eggshell is one of the fastest calcifying processes known and represents a unique model for studying biomineralization. Eggshell strength is a crucial economic trait for table egg production, and ensures that a safe egg reaches the consumer kitchen. However, a common toolkit for eggshell mineralization has not yet been defined. In this issue, label-free MS-based protein quantification technology has been used by Sun et al. (Proteomics 2013, 13, 3523-3536) to detect differences in protein abundance between eggshell matrix from strong and weak eggs and between the corresponding uterine fluids bathing strong and weak eggs. Proteins associated with the formation of strong eggshells are identified, which are now candidates for further investigations to define the regulatory relationship between specific eggshell matrix proteins and calcite crystal texture. PMID:24307661

  17. Synthesis of a Se0 /Calcite Composite Using Hydrothermal

    E-print Network

    Montes-Hernandez, German

    Synthesis of a Se0 /Calcite Composite Using Hydrothermal Carbonation of Ca(OH)2 CoupledVised Manuscript ReceiVed April 4, 2008 ABSTRACT: Elemental selenium (Se0 )/calcite composites were synthesized) deposited on the calcite matrix. Conversely, under O2-rich conditions, the composite consisted rod

  18. Sequestration of Selenium on Calcite Surfaces Revealed by Nanoscale Imaging

    E-print Network

    Montes-Hernandez, German

    Sequestration of Selenium on Calcite Surfaces Revealed by Nanoscale Imaging Christine V. Putnis, ISTerre, BP 53, F-38041 Grenoble, France *S Supporting Information ABSTRACT: Calcite, a widespread natural and for human health. In the form of selenite (Se(IV) ), selenium can be incorporated into calcite during growth

  19. Calcite Mineral Scaling Potentials of High-Temperature Geothermal Wells

    E-print Network

    Karlsson, Brynjar

    #12;i Calcite Mineral Scaling Potentials of High-Temperature Geothermal Wells Alvin I. Remoroza Faculty of Science University of Iceland 2010 #12;#12;iii Calcite Mineral Scaling Potentials of High #12;iv Calcite Mineral Scaling Potentials of High-Temperature Geothermal Wells 60 ECTS thesis

  20. Temperature limits for preservation of primary calcite clumped isotope paleotemperatures

    E-print Network

    Grossman, Ethan L.

    Temperature limits for preservation of primary calcite clumped isotope paleotemperatures Gregory A in the calcite lattice can alter the clumped isotope composition of paleotemperature archives such as fossil experiments involve heating fossil brachiopod calcite at different temperatures and times to directly observe

  1. Surface-Potential Heterogeneity of Reacted Calcite and Rhodochrosite

    E-print Network

    Surface-Potential Heterogeneity of Reacted Calcite and Rhodochrosite C H O N G Z H E N G N A , T R, nanostructures on the (101h4) surfaces of calcite and rhodochrosite are characterized by their surface potentials using Kelvin probe force microscopy. Water- induced nanostructures on calcite have a topographic height

  2. Preparation and formation mechanism of wood-block-like calcite particles

    SciTech Connect

    Guo Hua; Yu Jiaguo . E-mail: jiaguoyu@yahoo.com; Cheng Bei

    2006-08-15

    Pure calcite crystal with different morphologies such as wood-block and spherical aggregates were prepared by a precipitation reaction in the presence of citric acid. The as-prepared products were characterized with scanning electron microscope (SEM) and X-ray diffraction (XRD). The results showed that citric acid obviously influenced the formation of precipitates and the morphology of final products. The formation mechanism of wood-block-like particles was proposed according to theoretical deduction and the proposed growth mode. - Graphical abstract: Pure calcite crystal with different morphologies such as wood-block and spherical aggregates were prepared by a simple precipitation reaction in the presence of citric acid and the formation mechanism was proposed.

  3. Calcite Precipitation and Trace Metal Partitioning in Groundwater and the Vadose Zone: Remediation of Strontium-90 and Other Divalent Metals and Radionuclides in Arid Western Environments

    SciTech Connect

    Smith, Robert W.; Colwell, F. ''Rick'' S.; Ingram, Jani C.; Ferris, F. Grant; Reysenbach, Anna-Louise

    2001-08-09

    Radionuclide and metal contaminants are present in the vadose zone and groundwater throughout the U.S. Department of Energy (DOE) weapons complex. Demonstrating in situ immobilization of these contaminants in vadose zones or groundwater plumes is a cost-effective remediation strategy. However, the implementation of in situ remediation requires definition of the mechanism that controls sequestration of the contaminants. One such mechanism for metals and radionuclides is co-precipitation of these elements in authigenic calcite and calcite overgrowths. Calcite, a common mineral in many aquifers and vadose zones in the arid western U.S., can incorporate divalent metals such as strontium, cadmium, lead, and cobalt into its crystal structure by the formation of solid solutions. The rate at which trace metals are incorporated into calcite is a function of calcite precipitation kinetics, adsorption interactions between the calcite surface and the trace metal in solution, solid solution properties of the trace metal in calcite, and also the surfaces upon which the calcite is precipitating. A fundamental understanding of the coupling of calcite precipitation and trace metal partitioning and how this may occur in aquifers and vadose environments is lacking. The focus of the research proposed here is to investigate the facilitated partitioning of metal and radionuclides by their coprecipitation with calcium carbonate. Our specific research objectives include: (1) Elucidating the mechanisms and rates of microbially facilitated calcite precipitation and divalent cation adsorption/co-precipitation occurring in a natural aquifer as a result of the introduction of urea. (2) Assessing the effects of spatial variability in aquifer host rock and the associated hydro/biogeochemical processes on calcite precipitation rates and mineral phases within an aquifer.

  4. Calcite Precipitation and Trace Metal Partitioning in Groundwater and the Vadose Zone: Remediation of Strontium-90 and Other Divalent Metals and Radionuclides in Arid Western Environments

    SciTech Connect

    Smith, Robert W.; Colwell, F. ''Rick'' S.; Ingram, Jani C.; Ferris, F. Grant; Reysenbach, Anna-Louise

    2000-07-19

    Radionuclide and metal contaminants are present in the vadose zone and groundwater throughout the U.S. Department of Energy (DOE) weapons complex. Demonstrating in situ immobilization of these contaminants in vadose zones or groundwater plumes is a cost-effective remediation strategy. However, the implementation of in situ remediation requires definition of the mechanism that controls sequestration of the contaminants. One such mechanism for metals and radionuclides is co-precipitation of these elements in authigenic calcite and calcite overgrowths. Calcite, a common mineral in many aquifers and vadose zones in the arid western U.S., can incorporate divalent metals such as strontium, cadmium, lead, and cobalt into its crystal structure by the formation of solid solutions. The rate at which trace metals are incorporated into calcite is a function of calcite precipitation kinetics, adsorption interactions between the calcite surface and the trace metal in solution, solid solution properties of the trace metal in calcite, and also the surfaces upon which the calcite is precipitating. A fundamental understanding of the coupling of calcite precipitation and trace metal partitioning and how this may occur in aquifers and vadose environments is lacking. The focus of the research proposed here is to investigate the facilitated partitioning of metal and radionuclides by their coprecipitation with calcium carbonate. Our specific research objectives include: (1) Elucidating the mechanisms and rates of microbially facilitated calcite precipitation and divalent cation adsorption/co-precipitation occurring in a natural aquifer and vadose zone perched water body as a result of the introduction of urea. (2) Assessing the effects of spatial variability in aquifer host rock and the associated hydro/biogeochemical processes on calcite precipitation rates and mineral phases within an aquifer and a vadose zone perched water body.

  5. Kinetics and Mechanisms of Calcite Reactions with Saline Waters

    SciTech Connect

    Gorman, Brian P

    2015-09-02

    Project Description: The general objective of the proposed research is to determine the kinetics and mechanisms of calcite reactions with saline waters over a wide range of saline water composition, pCO2, 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 calcite 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 pCO2, Ca2+, 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 CO2 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 seed 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 calcite substrates and in a wide range of supersaturation conditions did not indicate any ACC layer. Instead, an epitaxial layer by layer growth mechanism was confirmed by grazing incidence X-ray diffraction, µ-Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and electron diffraction. Extended time studies out to 45 days confirmed the epitaxial relationship of the overgrowth layer with the substrate. Under NSW conditions, overgrowths were found to have ~0.4 to 0.8 nm / hr growth rates and accommodating 4 at% Mg, resulting in a highly strained overgrowth layer. Following the initial layer by layer growth mechanism, the growth changes to Stranski-Krastanov type after a critical thickness of approximately 100 nm.

  6. Orientation and Mg Incorporation of Calcite Grown on Functionalized Self-Assembled Monolayers: A Synchrotron X-ray Study

    SciTech Connect

    Kwak,S.; DiMasi, E.; Han, Y.; Aizenberg, J.; Kuzmenko, I.

    2005-01-01

    Calcite crystals were nucleated from MgCl2/CaCl2 solutions onto functionalized self-assembled monolayers adsorbed onto E-beam evaporated Au films. Synchrotron X-ray scattering studies of the crystals reveal new information about preferred orientation and Mg incorporation. The Au [111] axis is distributed within 2.6 degrees of the film surface normal, but the oriented crystals may be tilted up to 6 degrees away from this axis. For low Mg{sup 2+} content, SO{sub 3}--functionalized films nucleated primarily near the (106) calcite face, odd-chain-length carboxylic acid terminated alkanethiol films nucleated near the (012) face, and even-chain-length carboxylic acid terminated alkanethiol films nucleated near the (113) face. [Mg{sup 2+}]/[Ca{sup 2+}] concentration ratios (n) of 2 and greater defeated this preferred orientation and created a powder texture. Diffraction patterns within the layer plane from the coarse calcite powders indicated a shift to higher 2 accompanied by peak broadening with increasing n. For 0.5 < n < 3.5, a double set of calcite peaks is observed, showing that two distinct Mg calcite phases form: one of comparatively lower Mg content, derived from the templated crystals, and a Mg-rich phase derived from amorphous precursor particles. According to the refinement of lattice parameters, Mg incorporation of up to 18 mol % occurs for n = 4, independent of film functionality. We discuss the differences between the differently functionalized monolayers and also introduce the hypothesis that two separate routes to Mg calcite formation occur in this system.

  7. in situ Calcite Precipitation for Contaminant Immobilization

    SciTech Connect

    Yoshiko Fujita; Robert W. Smith

    2009-08-01

    in situ Calcite 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 calcite. Calcite, 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 calcite 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 calcite 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 a well (which can lead to clogging). A final particularly attractive characteristic of this approach is its long-term sustainability; the remediation scheme is geared toward environments that are already saturated with respect to calcite, and in such systems the bulk of any newly precipitated calcite will remain stable once engineered manipulations cease. This means that the co-precipitated contaminants will be effectively sequestered over the long term. We are currently conducting integrated field, laboratory, and computational research to evaluate a) the relationships between urea hydrolysis rate, calcite precipitation rate, and trace metal partitioning under environmentally relevant conditions; and b) the coupling between flow/flux manipulations and calcite precipitate distribution and metal uptake. We are also assessing the application of geophysical and molecular biological tools to monitor the relevant chemical and physical processes. The primary emphasis is on field-scale processes, with the laboratory and modeling activities designed specifically to support the field studies. Field experiments are being conducted in perched water (vadose zone) at the Vadose Zone Research Park (VZRP) at the Idaho National Laboratory; the VZRP provides an uncontaminated setting that is an analog of the 90Sr-contaminated vadose zone at the Idaho Nuclear Technology and Engineering Center. A summary of results to date will be presented.

  8. Crystallization of monosodium urate monohydrate

    NASA Astrophysics Data System (ADS)

    Burt, Helen M.; Dutt, Yougesh C.

    1989-01-01

    The crystallization kinetics of monosodium urate monohydrate (MSUM) at 37°C have been investigated by seeding mechanically stirred supersaturated MSUM solutions with well characterized seed crystals. A second order dependence of the crystallization rate on supersaturation was found and rate constants were determined using an integrated from of the general equation for crystallization. At relative supersaturations of 2.6 and low seed concentrations, induction periods indicative of secondary nucleation were observed. The induction period could be eliminated by increasing the seed concentration.

  9. Evolution of calcite growth morphology in the presence of magnesium: Implications for the dolomite problem

    NASA Astrophysics Data System (ADS)

    Hong, Mina; Xu, Jie; Teng, Henry H.

    2016-01-01

    The effect of magnesium on calcite growth morphology was known to occur as step rounding in some cases and surface segmentation in others. What remains unknown are the conditions for and the relations between the different effects, suggesting a lack of comprehensive understanding of the fundamental cause. Here we investigated the evolution of spiral hillock morphology on calcite cleavage surfaces in solutions with increasing Ca to Mg ratios and supersaturation levels using in situ atomic force microscopy. We isolated the effects of Mg and saturation by conducting experiments under conditions of constant pH, ionic strength, and Ca2+/CO32-. Our results revealed three types of morphological variations, ranging from step rounding in one direction (type I), to all directions (type II), and finally to a mosaic-like surface segmentation associated with monolayer buckling and step bunching (type III). These results suggest that the effect of magnesium on calcite growth depends upon multiple parameters including the concentration of Mg in solution, the step speed, as well as the extensiveness of Mg for Ca substitution in calcite lattice. We propose that the morphological variation may be understood by a model taken into consideration of (1) the lifespan and flux size of Mg ions at kinks in comparison to step kinetics, and (2) the diffusion and alignment of point defects created by the substitution of Mg for Ca in the crystal lattice. Stress calculations show that the maximum amount of Mg which calcite lattice can sustain before plastic deformation is ?40%, suggesting that lattice stress due to the mismatch between MgCO3 and CaCO3 is likely the ultimate cause for the difficulty of ambient condition dolomite crystallization.

  10. Ca-Doped Strontianite-Calcite Hybrid Micropillar Arrays Formed via Oriented Dissolution and Heteroepitaxial Growth on Calcite

    E-print Network

    Qi, Limin

    Ca-Doped Strontianite-Calcite Hybrid Micropillar Arrays Formed via Oriented Dissolution and Heteroepitaxial Growth on Calcite Weike Wu,, Yurong Ma,*, Ying Xing,§ Yuzhe Zhang, Heng Yang, Qiang Luo,§ Jian dissolution up to now. In this work, well ordered single crystalline calcium-doped strontianite-calcite hybrid

  11. Calcite growth-rate inhibition by fulvic acid and magnesium ion—Possible influence on biogenic calcite formation

    USGS Publications Warehouse

    Reddy, Michael M.

    2012-01-01

    Increases in ocean surface water dissolved carbon dioxide (CO2) concentrations retard biocalcification by reducing calcite supersaturation (?c). Reduced calcification rates may influence growth-rate dependent magnesium ion (Mg) incorporation into biogenic calcite modifying the use of calcifying organisms as paleoclimate proxies. Fulvic acid (FA) at biocalcification sites may further reduce calcification rates. Calcite growth-rate inhibition by FA and Mg, two common constituents of seawater and soil water involved in the formation of biogenic calcite, was measured separately and in combination under identical, highly reproducible experimental conditions. Calcite growth rates (pH=8.5 and ?c=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 calcite growth-rate inhibitor as FA. Calcite 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 calcite growth rates by substitution for calcium ion at the growth site. In contrast, FA inhibits calcite growth rates by binding multiple carboxylate groups on the calcite surface. FA and Mg together have an increased affinity for the calcite growth sites reducing calcite growth rates.

  12. Dissolution Kinetics of Biogenic Magnesian Calcites

    NASA Astrophysics Data System (ADS)

    Thompson, R.; Guidry, M.; Mackenzie, F. T.; De Carlo, E. H.

    2014-12-01

    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 calcite (Mg-calcite) calcifiers found in shallow-water reef and other carbonate environments. Many Mg-calcite 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-calcite 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-calcite 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 ?mol 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 dissolution for a broad range of Mg-calcite phases, along with determination of sediment mineralogy, is necessary to allow managers to model and predict quantitatively the impacts of OA on a variety of coral reef and other carbonate-dominated sedimentary environments.

  13. The Influence of Temperature, pH, and Growth Rate on the Stable Isotope Composition of Calcite

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The oxygen isotope composition of carbonate minerals varies with temperature as well as other environmental variables. For carbonates that precipitate slowly, under conditions that approach thermodynamic equilibrium, the temperature-dependence of 18O uptake is the dominant signal and the measured 18O content can be used as a paleotemperature proxy. In the more common case where carbonate minerals grow in a regime where they are not in isotopic equilibrium with their host solution, their stable isotope compositions are a convolution of the effects of multiple environmental variables. We present results from inorganic calcite growth experiments demonstrating the occurrence of non-equilibrium oxygen isotope effects that vary systematically with pH and crystal growth rate. We have developed an isotopic ion-by-ion crystal growth model that quantifies the competing roles of temperature, pH, and growth rate, and provides a general description of calcite-water oxygen isotope fractionation under non-equilibrium conditions. The model predicts that (1) there are both equilibrium and kinetic contributions to calcite oxygen isotopes at biogenic growth rates, (2) calcite does not inherit the stable isotopic composition of dissolved inorganic carbon (DIC), (3) for oxygen isotopes there is a kinetically controlled variation of about 1‰ per pH unit between pH=7.7 and 9.3 at constant growth rate for inorganic calcite as well as the foraminifera Orbulina universa, and (4) extreme light isotope enrichments in calcite in alkaline environments are likely due to disequilibrium among DIC species in aqueous solution. The experimental and modeling approaches can be extended to carbon isotope as well as clumped isotope uptake into calcite but additional data are needed to constrain the kinetic fractionation factors for carbon isotopes and doubly-substituted isotopologues. The results will be discussed in the context of separating the relative influence of inorganic and biologic processes on isotopic fractionation.

  14. Intrinsic versus extrinsic controls on the development of calcite dendrite bushes, Shuzhishi Spring, Rehai geothermal area, Tengchong, Yunnan Province, China

    NASA Astrophysics Data System (ADS)

    Jones, Brian; Peng, Xiaotong

    2012-04-01

    In the Rehai geothermal area, located near Tengchong, there is an old succession of crystalline calcite that formed from a spring that is no longer active. The thin-bedded succession, exposed on the south bank of Zaotang River, is formed of three-dimensional dendrite bushes that are up to 6 cm high and 3 cm in diameter with multiple levels of branching. Bedding is defined by color, which ranges from white to gray to almost black and locally accentuated by differential weathering that highlights the branching motif of the dendrites. The succession developed through repeated tripartite growth cycles that involved: Phase I that was characterized by rapid vertical growth of the dendrite bushes with ever-increasing branching; Phase II that developed once growth of the dendrites had almost or totally ceased, and involved an initial phase of etching that was followed by the precipitation of various secondary minerals (sheet calcite, trigonal calcite crystals, hexagonal calcite crystals, hexagonal plates formed of Ca and P, Mn precipitates, Si-Mg reticulate coatings, opal-CT lepispheres) on the branches of the calcite dendrites, and Phase III that involved deposition of detrital quartz, feldspar, clay, and calcite on top of the dendrite bushes. The tripartite growth cycle is attributed primarily to aperiodic cycles in the CO2 content of the spring water that was controlled by subsurface igneous activity rather than climatic controls. High CO2 coupled with rapid CO2 degassing triggered growth of the dendrite bushes. As CO2 levels waned, saturation levels in the spring water decreased and calcite dendrite growth ceased and precipitation of the secondary minerals took place, possibly in the microcosms of microbial mats. Deposition of the detrital sediment was probably related to surface runoff that was triggered by periods of high rainfall. Critically, this study shows that intrinsic factors rather than extrinsic factors (e.g., climate) were the prime control on the development of the tripartite growth cycle.

  15. Arsenate Uptake by Calcite: Macroscopic and Spectroscopic Characterization of Adsorption and Incorporation Mechanisms

    SciTech Connect

    Alexandratos,V.; Elzinga, E.; Reeder, R.

    2007-01-01

    Batch uptake experiments and X-ray element mapping and spectroscopic techniques were used to investigate As(V) (arsenate) uptake mechanisms by calcite, including adsorption and coprecipitation. Batch sorption experiments in calcite-equilibrated suspensions (pH 8.3; PCO{sub 2} = 10{sup -3.5} atm) reveal rapid initial sorption to calcite, with sorption rate gradually decreasing with time as available sorption sites decrease. An As(V)-calcite 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}. Calcite single crystals 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 calcite 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 calcite surface, similar to often-cited analog phosphate, and uptake can occur via both adsorption and coprecipitation reactions. Therefore, calcite may be effective for partial removal of dissolved arsenate from aquatic and soil systems.

  16. Nanoscale effects of strontium on calcite growth: An in situ AFM study in the absence of vital effects

    NASA Astrophysics Data System (ADS)

    Wasylenki, Laura E.; Dove, Patricia M.; Wilson, Darren S.; De Yoreo, James J.

    2005-06-01

    This experimental study presents in situ measurements of step migration rates for layer growth of calcite at various levels of superaturation and fluid Sr concentrations. Our results show that Sr has complex behavior as an impurity. At low concentrations, Sr promotes faster growth. This effect may be associated with slight shifts in calcite solubility when Sr is incorporated or may be due to as yet uncharacterized kinetic effects. At higher concentrations, Sr stops step advancement by pinning kink-sites or step edges. The threshold concentration of Sr needed to halt growth is positively correlated with supersaturation. Addition of Sr to the calcite growth system leads to significant changes in hillock morphology. Hillocks become elongate perpendicular to the projection of the c-glide plane, in contrast to the changes previously reported for Mg. Step edges also become scalloped, and the boundary between the obtuse-stepped flanks disappears and is replaced by a new step direction with edges parallel to [010]. Incorporation of Sr was measured at two supersaturation levels and identical fluid [Sr]. The results indicate a strong positive correlation between fluid supersaturation and crystal Sr content. Further, Sr is strongly fractionated between obtuse- and acute-stepped flanks by a factor of approximately two. The sensitivity of Sr uptake to supersaturation may explain apparently contradictory results in the literature regarding whether Sr uptake in the calcite produced by one-celled marine organisms is controlled by temperature. In addition, Sr contents of natural calcite samples may be good indicators of the levels of supersaturation at which the crystals grew. Results of this investigation demonstrate the importance of understanding impurity-specific interactions with calcite growth surfaces at the microscopic scale. Despite similar chemical behavior in some systems, Mg and Sr clearly have very different effects on calcite growth. If Sr and other impurities are to be used as robust indicators of growth conditions in natural calcite samples, well grounded understanding of the mechanisms of recording trace element signatures in calcite is an essential step toward correctly deciphering paleoenvironmental signals from fossil calcite compositions.

  17. Magnesian calcite sorbent for carbon dioxide capture.

    PubMed

    Mabry, James C; Mondal, Kanchan

    2011-01-01

    Magnesian calcite 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 calcite 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. PMID:21473269

  18. Stable isotope composition alteration produced by the aragonite-to-calcite transformation in speleothems and implications for paleoclimate reconstructions

    NASA Astrophysics Data System (ADS)

    Zhang, Haiwei; Cai, Yanjun; Tan, Liangcheng; Qin, Shijiang; An, Zhisheng

    2014-07-01

    Aragonite, a mineralogical constituent of speleothems in cave environments, is unstable and susceptible to inversion to calcite, a diagenetic process that involves changes in the mineralogy, texture and geochemistry of speleothems. However, the exact alterations of stable isotope compositions during such diagenesis have not been fully investigated. In this study, two aragonite stalagmites (SN3 and SN15) from the Shennong Cave, southeast China, were found partially inverted to calcite, as determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses, and thin-section inspections under microscope. The fiber relics and textural ghosts of aragonite preserved in coarse and equant mosaic calcite crystals clearly indicate that the calcite in these two stalagmites were inverted from aragonite. The stable isotope compositions (?13C and ?18O, given in per mil versus VPDB standard) of primary aragonite and secondary calcite were analyzed and compared, along both growth layers and growth axes. The results show that, along growth layers, differences of ?13C values between aragonite and calcite are negligible (0.1‰-0.2‰), whereas differences of ?18O values between aragonite and calcite are significant (0.63‰-0.87‰). Comparisons along growth axes show similar results: i.e., differences of ?13C values are negligible (0.06‰ ± 0.22‰) whereas differences of ?18O values are significant (0.85‰ ± 0.29‰). Most likely, the aragonite in SN3 and SN15 were internally inverted by interactions of trace calcite crystallites and pore water within intercrystalline pore spaces, by a dissolution-reprecipitation process occurring in trapped pore water. In the case of the inversion of aragonite to calcite in speleothems, such as that observed in SN3 and SN15, the ?13C values could be used in paleoclimate and paleoenvironment reconstructions because they are inherited from those of primary aragonite. Although the ?18O values might be cross-calibrated to those of primary aragonite if the aragonite-calcite fractionation offset is known (e.g., 0.85‰ ± 0.29‰ in this study), however, the ?18O values of secondary calcite should be used with caution in such reconstructions as the ?18O offset value is not consistently invariable.

  19. Kinetics and Mechanisms of Cadmium Carbonate Heteroepitaxial Growth at the Calcite (101¯4) Surface

    SciTech Connect

    Xu, Man; Kovarik, Libor; Arey, Bruce W.; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien N.

    2014-06-01

    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 calcite-water interfaces was investigated by exposing calcite (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 crystallization 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 calcite substrate. Cross-sectional transmission electron microscopy (TEM) images reveal that the atomic structure of the interface between the cadmium carbonate coating and calcite shows perfect, dislocation-free epitaxy.

  20. Frictional behavior of talc-calcite mixtures

    NASA Astrophysics Data System (ADS)

    Giorgetti, C.; Carpenter, B. M.; Collettini, C.

    2015-09-01

    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 calcite 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 calcite 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 calcite 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 calcite 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.

  1. Physical and stable-isotope evidence for formation of secondary calcite and silica in the unsaturated zone, Yucca Mountain, Nevada

    USGS Publications Warehouse

    Whelan, J.F.; Paces, J.B.; Peterman, Z.E.

    2002-01-01

    Calcite 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 calcite??fluorite??zeolites that is frequently capped by chalcedony??quartz. Intermediate- and late-stage deposits consist largely of calcite, commonly with opal on buried growth layers or outermost crystal faces of the calcite. 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 calcite blades up to several cms in length. These blades may be capped with knobby or corniced overgrowths of late-stage calcite 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 crystals by surface tension and evaporated at the crystal tips. Fluid inclusion studies have shown that most early-stage and some intermediate-stage calcite formed at temperatures of 35 to 85??C. Calcite 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 calcite ??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 gradual cooling of nearby plutons. The physical restriction of the deposits (and, therefore, fluid flow) to fracture footwalls and cavity floors and the heterogeneous and limited distribution of the deposits provides compelling evidence that they do not reflect flooding of the thick UZ at Yucca Mountain. The textures and isotopic and chemical compositions of these mineral deposits are consistent with deposition in a UZ setting from meteoric waters percolating downward along fracture flow paths.

  2. Characterization and In-Situ Monitoring of ZnSe Crystal Growth by Seeded PVT for Microgravity Applications

    NASA Technical Reports Server (NTRS)

    Feth, Shari T.

    2001-01-01

    Crystal 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 crystal 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 crystal growth of ZnSe by PVT (P.I.: Su of NASA/MSFC) will help to clarify the effects of convection on crystal growth. A crystal growth furnace with in-situ and real time optical monitoring capabilities was constructed and used to monitor the vapor composition and growing crystal 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.

  3. Selectively increasing of polyunsaturated (18:2) and monounsaturated (18:1) fatty acids in Jatropha curcas seed oil by crystallization using D-optimal design

    PubMed Central

    2012-01-01

    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 seed 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, crystallization temperature and crystallization 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, crystallization temperature of ?10°C and 24 h of crystallization 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

  4. Adsorption of ethanol and water on calcite: dependence on surface geometry and effect on surface behavior.

    PubMed

    Keller, K S; Olsson, M H M; Yang, M; Stipp, S L S

    2015-04-01

    Molecular dynamics (MD) simulations were used to explore adsorption on calcite, 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 calcite crystal 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 crystal faces are more stabilized because of their surface geometry. The -O(H) functional group on ethanol forms tight bonds with calcite; the nonpolar, -CH3 ends, which point away from the surface, create a hydrophobic layer that changes surface charge, thus wettability, and partly protects calcite from precipitation and dissolution. These tricks could easily be adopted by biomineralizing organisms, allowing them to turn on and off crystal growth. They undoubtedly also play a role in the wetting properties of mineral surfaces in commercial CaCO3 manufacture, oil production, and contamination remediation. PMID:25790337

  5. The effect of preincubation of seed crystals of uric acid and monosodium urate with undiluted human urine to induce precipitation of calcium oxalate in vitro : implications for urinary stone formation.

    PubMed Central

    Grover, Phulwinder K.; Ryall, Rosemary L.

    2002-01-01

    BACKGROUND: Previous studies demonstrated that crystals 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 seeds 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 seed crystals of UA, NaU and CaOx (6 mg/100 ml) on CaOx crystallization were compared in a solution with the same crystals that had been preincubated for 3 hours with healthy male urine. A Coulter Counter was used to follow the crystallization 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 seeds 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 seeds 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 seed crystals 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 seed crystals of UA and NaU, untreated and treated, were attached like barnacles upon the surfaces of CaOx crystals which themselves were bigger than those precipitated in the presence of CaOx seeds. SDS-PAGE analysis of the demineralized treated seeds showed that they all selectively adsorbed urinary proteins, and perhaps other urinary macromolecules and low molecular weight components, on their surface. CONCLUSIONS: It was concluded that preincubation with urine, such as occurs in vivo, only slightly reduces the ability of seed crystals of CaOx, but not of UA, to cause deposition of CaOx. The most striking effect was on NaU seeds where the preincubation quite dramatically attenuated their promotory effect on the mineral deposition. This may explain the discrepancy between findings of studies carried out in inorganic solutions and undiluted human urine. This stresses the invalidity of directly extrapolating results obtained in inorganic solutions to likely effects in urine and more importantly, on stone formation. PMID:12456991

  6. Tuning calcite morphology and growth acceleration by a rational design of highly stable protein-mimetics

    SciTech Connect

    Chen, Chunlong; Qi, Jiahui; Tao, Jinhui; Zuckermann, Ronald; De Yoreo, James J.

    2014-09-05

    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 crystal formation. Here, we demonstrate that both the morphology and the degree of acceleration or inhibition observed during growth of calcite 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-crystal binding energies and observed changes in calcite 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 crystallization promoters, and offers a straightforward screening method based on macroscopic crystal morphology. Because peptoids are sequence-specific, highly stable, and easily synthesized, peptoid-enhanced crystallization offers a broad range of potential applications.

  7. Tuning calcite morphology and growth acceleration by a rational design of highly stable protein-mimetics

    NASA Astrophysics Data System (ADS)

    Chen, Chun-Long; Qi, Jiahui; Tao, Jinhui; Zuckermann, Ronald N.; Deyoreo, James J.

    2014-09-01

    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 crystal formation. Here, we demonstrate that both the morphology and the degree of acceleration or inhibition observed during growth of calcite in the presence of peptoids can be rationally tuned by balancing the electrostatic and hydrophobic interactions, with hydrophobic interactions playing the dominant role. While either strong electrostatic or hydrophobic interactions inhibit growth and reduces expression of the {104} faces, correlations between peptoid-crystal binding energies and observed changes in calcite growth indicate moderate electrostatic interactions allow peptoids to weakly adsorb while moderate hydrophobic interactions cause disruption of surface-adsorbed water layers, leading to growth acceleration with retained expression of the {104} faces. This study provides fundamental principles for designing peptoids as crystallization promoters, and offers a straightforward screening method based on macroscopic crystal morphology. Because peptoids are sequence-specific, highly stable, and easily synthesized, peptoid-enhanced crystallization offers a broad range of potential applications.

  8. Occurrence of microdiamond in UHP calcite marble from the Kokchetav Massif

    NASA Astrophysics Data System (ADS)

    Ogasawara, Y.; Adachi, T.; Aoki, K.

    2004-12-01

    Small amount of microdiamond was discovered in UHP calcite marble from Kumdy-kol, the Kokchetav Massif northern Kazakhstan. UHP calcite marble is characterized by 1) pure calcite (after aragonite) is only one carbonate phase, 2) presence of titanite, K-feldspar and diopside with phengite and K-feldspar lamella, 3) coesite exsolution from supersilicic titanite. This marble contains UHP evidence as coesite of exsolution origin in titanite and lamella texture in diopside. Minimum P condition was constrained as 6 GPa by precursor composition of titanite. So far, we have described this calcite marble as diamond-free UHP carbonate rock (Ogasawara et al., 2002); however, our recent observation found microdiamond in some domains (B-type) of this rock. Microdiamond occurs only in diopside and its amount is very low compared with diamond-bearing dolomite marble. We found 61 microdiamond grains in two thin sections (c.f. in dolomite marble, highest concentration domain contains over 4000 grains in one thin section). Microdiamond grains are heterogeneously distributed in some layers. The domain (A-type) containing relatively large amount of titanite does not contain diamond. The microdiamond in calcite marble shows 3 to 20 micrometers in diameter, rounded or cubic form, pale yellowish color and translucent character. Laser Raman spectroscopy indicated that FWHM of a Raman band at about 1332 cm-1 ranges from 2.99 to 3.64 cm-1 (average: 3.28 cm-1) and this average value is the smallest among core of S-type, rim of S-type, R-type and diamond in gneiss. Based on the morphology and other features except for FWHM of Raman band, the microdiamond in calcite marble is similar to R-type in dolomite marble (Ishida et al., 2003). No S-type diamond (_gStar_h-shaped form with core and rim) occurs in this calcite marble, and this indicates that the second stage growth of microdiamond probably from multicomponent aqueous fluid had not occurred in calcite marble. Low amount of microdiamond occurs only in diopside, no diamond occurs in titanite (stable at extremely low-XCO2 conditions), and lack of the second stage growth of microdiamond in calcite marble; all these features may be related with extremely low-XCO2 condition under UHP metamorphism. One of the possible explanations for this diamond occurrence is that microdiamonds in calcite marble are relic crystal formed before the second stage growth (the rim stage of S-type microdiamond in dolomite marble). Therefore, it is very important to confirm whether these microdiamond in B-type calcite marble had been growing or dissolving under such extremely low-XCO2 conditions. References Ishida et al. (2003): Journal of Metamorphic Geology, Vol. 21, p. 515-522. Ogasawara et al. (2000): The Island Arc, Vol. 9, p. 400-416. Ogasawara et al. (2002): American Mineralogist, Vol. 87, p. 454-461.

  9. New Shocked Calcite and Fe Grains from Noerdlingen Ries Impact Crater

    NASA Astrophysics Data System (ADS)

    Miura, Y.

    1995-09-01

    Shocked minerals with simple chemical composition of silica, carbon or iron material reveal high-pressure phase during compression process [1]. As calcite 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 calcite 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 calcite 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 calcites show low X-ray intensity and high Bragg angle shift. compared with standard calcite 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 crystal 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 calcite: rho=2.71g/cm^3) of the calcite cell which is the same characters of shocked phases of quartz or graphite [1,2,3,4] (Table 1). Anomalous calcite 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 calcite with high density from Ries and artificial impact craters, appears here in the hard copy. Two types of shocked calcites are found in artificial impact experiments of railgun of the ISAS. Japan. (a) Shocked calcite formed on oxidation condition (near the rim of vapor plume of impact [7]). (b)Shocked calcite formed on reduction condition (interior of vapor plume of impact [7]). The shocked calcites of the Buschelberg (R8) inside the crater are correspondent to shocked calcite with reduction state. which suggests recrystallization inside the crater. The detailed experiments of the R8 samples are checked on yellow (Fe-rich) colored sample of R8Yl and white colored sample (R8W). From the X-ray diffraction data of Bragg angle shift, the R8W1 is more close to reduction state during impact. The shocked calcites under oxidation state are formed as non-stoichiometric compound (and high density) after gas of C02 formation mainly near rim of vapor plume, which is the same data of artificial impact experiments of oxidation condition (i.e. sample No. LSRGl). The shocked calcite under reduction state are formed relatively as normal calcite (with normal or a little high density) and carbon after formation of gaseous materials of CO, 02 and Ca. Thus cabon source from target rock of limestone [2,3,4] can be explained as reduction formation of impact, as listed in Table 2. Table 2, showing, the formation process of shocked calcite materials by shock impact, appears here in the hard copy. References [1] Miura Y.(l991): Shock Waves, 1, 135-141. ?2] Miura Y. (1994): Proc. ISAS Lunar & Planet. Sci. (ISAS, Japan), 27, 204-207. [3] Miura Y. et al. (1995): Shock Waves, Japan, 613-624. [4] Miura Y. and Okanoto M. (19995): Antarctic Meteorites (NIP?), 20, 169-171. ?1989): Tma;l(-.t. r?r;lt.?rin? ?rhrfnr? llniv?r?i?v Pr? )A? 7?;

  10. Impact of trace metals on the water structure at the calcite surface

    NASA Astrophysics Data System (ADS)

    Wolthers, Mariette; Di Tommaso, Devis; De Leeuw, Nora

    2014-05-01

    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 calcite 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 calcite (10-14) surface. We have performed Molecular Dynamics simulations of metal-doped calcite 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 calcite affect its reactivity. The information obtained in this study will help in improving existing macroscopic surface model for the reactivity of calcite [2] and give more general insight in mineral surface reactivity in relation to crystal 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.

  11. Basal slip and texture development in calcite: new results from torsion experiments

    SciTech Connect

    Barber, D. J.; Wenk, H.-R.; Gomez-Barreiro, J.; Rybacki, E.; Dresen, G.

    2008-06-09

    The deformation behavior of calcite has been of longstanding interest. Through experiments on single crystals, 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 calcite single crystals 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 calcite rocks at high temperature can now be explained, resolving a long-standing puzzle.

  12. Textural properties of synthetic nano-calcite produced by hydrothermal carbonation of calcium hydroxide

    E-print Network

    Montes-Hernandez, German; Charlet, L; Tisserand, Delphine; Renard, F

    2008-01-01

    The hydrothermal carbonation of calcium hydroxide (Ca(OH)2) at high pressure of CO2 (initial PCO2 1/4 55 bar) and moderate to high temperature (30 and 90 1C) was used to synthesize fine particles of calcite. This method allows a high carbonation efficiency (about 95% of Ca(OH)2-CaCO3 conversion), a significant production rate (48 kg/m3 h) and high purity of product (about 96%). However, the various initial physicochemical conditions have a strong influence on the crystal size and surface area of the synthesized calcite crystals. The present study is focused on the estimation of the textural properties of synthesized calcite (morphology, specific surface area, average particle size, particle size distribution and particle size evolution with reaction time), using Rietveld refinements of X-ray diffraction (XRD) spectra, Brunauer-Emmett-Teller (BET) measurements, and scanning electron microscope (SEM) and transmission electron microscope (TEM) observations. This study demonstrate that the pressure, the temperatu...

  13. Biomineralization processes of calcite induced by bacteria isolated from marine sediments.

    PubMed

    Wei, Shiping; Cui, Hongpeng; Jiang, Zhenglong; Liu, Hao; He, Hao; Fang, Nianqiao

    2015-06-01

    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 calcite. Scanning electron microscopy showed that morphologies of the minerals were dominated by cubic, rhombic and polygonal plate-like crystals. The dynamic process of microbial calcium carbonate precipitation revealed that B. lentus CP28 precipitated calcite crystals through the enzymatic hydrolysis of urea, and that when ammonium ion concentrations reached 746 mM and the pH reached 9.6, that favored calcite 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

  14. Biomineralization processes of calcite induced by bacteria isolated from marine sediments

    PubMed Central

    Wei, Shiping; Cui, Hongpeng; Jiang, Zhenglong; Liu, Hao; He, Hao; Fang, Nianqiao

    2015-01-01

    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 calcite. Scanning electron microscopy showed that morphologies of the minerals were dominated by cubic, rhombic and polygonal plate-like crystals. The dynamic process of microbial calcium carbonate precipitation revealed that B. lentus CP28 precipitated calcite crystals through the enzymatic hydrolysis of urea, and that when ammonium ion concentrations reached 746 mM and the pH reached 9.6, that favored calcite 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

  15. Carbonates in thrust faults: High temperature investigations into deformation processes in calcite-dolomite systems

    NASA Astrophysics Data System (ADS)

    Kushnir, A.; Kennedy, L.; Misra, S.; Benson, P.

    2012-04-01

    The role of dolomite on the strength and evolution of calcite-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 calcite, 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, calcite-dolomite composites of relatively low dolomite content. The effect of dolomite on limestone rheology, the onset of crystal-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 calcite-dolomite composites. Experiments were performed on samples produced by hot isostatic pressing (HIP) amalgams of a natural, pure dolomite and a reagent, pure calcite. 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 shows that small dolomite grains (~50 ?m) are characterized by well-defined grain boundaries and cleavage controlled fracture. There is evidence of the interruption of foliation development due to the presence of large-grained dolomite. Calcite grains are characterized by triple junction grain boundaries, providing evidence for recrystallization. Ongoing microstructural analyses (including: thin section analysis, EBSD, SEM, and Microprobe analysis) are being conducted to better constrain the deformation mechanisms and the degree of strain localization in these composites. Our experiments provide insights into the processes controlling rheology within bimodal calcite-dolomite systems, which can be used to improve models of the evolution of fold and thrust belt systems.

  16. Removal of organic magnesium in coccolithophore calcite

    NASA Astrophysics Data System (ADS)

    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.

    2012-07-01

    Coccolithophore calcite 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 calcite 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 calcite. 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 (Fe/Ca and P/Ca) make this protocol applicable to field and laboratory studies of trace elemental composition in coccolithophore calcite.

  17. Fibrous calcite from the Middle Ordovician Holston Formation (east Tennessee)

    SciTech Connect

    Tobin, K.J.; Walker, K.R. . Dept. of Geological Sciences)

    1993-03-01

    Fibrous calcite 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 calcite (mainly radiaxial fibrous) occur most commonly as cements in mainly stromatactis structures present in bioherms and intergranular porosity in beds that flank bioherms. Fibrous calcite is interpreted to have been precipitated in a marine setting. Fibrous calcite is uniformly turbid or banded with interlayered turbid and clearer cement. Fibrous calcite most commonly shows patchy or blotchy dull-non-luminescence under cathodoluminescence. Bands of uniformly non-luminescent and relatively bright luminescent calcite are present. [delta][sup 13]C compositions of fibrous calcite 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 calcite ([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 calcite reflect addition of post-depositional calcite during stabilization. Most enriched [delta][sup 13]C and [delta][sup 18]O fibrous calcite 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 calcite precipitated in isotopic equilibrium with Middle Ordovician sea water.

  18. The influence of temperature, pH, and growth rate on the ?18O composition of inorganically precipitated calcite

    NASA Astrophysics Data System (ADS)

    Watkins, James M.; Hunt, Jonathan D.; Ryerson, Frederick J.; DePaolo, Donald J.

    2014-10-01

    The oxygen isotope composition of carbonate minerals varies with temperature as well as other environmental variables. For carbonates that precipitate slowly, under conditions that approach thermodynamic equilibrium, the temperature-dependence of 18O uptake is the dominant signal and the measured 18O content can be used as a paleotemperature proxy. In the more common case where carbonate minerals grow in a regime where they are not in isotopic equilibrium with their host solution, their oxygen isotope compositions are a convolution of multiple environmental variables. Here we present results from calcite growth experiments demonstrating the occurrence of large (>2‰) non-equilibrium oxygen isotope effects under conditions relevant to biogenic calcite growth and many natural inorganic systems. We show that these non-equilibrium effects vary systematically with pH and crystal growth rate. An isotopic ion-by-ion crystal growth model quantifies the competing roles of temperature, pH, and growth rate, and provides a general description of calcite-water oxygen isotope fractionation under non-equilibrium conditions. The crystal growth model results show that (1) there are both equilibrium and kinetic contributions to calcite oxygen isotopes at biogenic growth rates, (2) calcite does not directly inherit the oxygen isotope composition of DIC even at fast growth rates, (3) there is a kinetically controlled variation of about 1‰ per pH unit between pH=7.7 and 9.3 at constant growth rate for inorganic calcite as well as biogenic calcite, and (4) extreme light isotope enrichments in calcite in alkaline environments are likely due to disequilibrium among DIC species in aqueous solution. The model can be extended to 13C uptake into carbonates as well as clumped isotopes but additional data are needed to constrain the kinetic fractionation factors for carbon isotopes. The experimental and model results constitute an important step in separating the relative influence of inorganic and biologic processes on isotopic fractionation and may aid the development of new paleoproxies based on non-equilibrium effects.

  19. Dissolution dynamics of the calcite-water interface observed in situ by glancing-incidence X-ray scattering

    SciTech Connect

    Sturchio, N.C.; Chiarello, R.P.

    1995-06-02

    Glancing-incidence X-ray scattering measurements made at the National Synchrotron Light Source were used to investigate dissolution dynamics in situ at the calcite-water interface. The relation between calcite saturation state and roughness of the calcite (1014) cleavage surface as a function of time was examined during pH titrations of an initially calcite-saturated solution. Systematic variations in roughness were observed as a function of saturation state as pH was titrated to values below that of calcite 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-crystal dissolution studies by atomic force microscopy. These data indicate some important potential applications of GIXS in the study of mineral-water interface geochemistry.

  20. Spectroscopic characterization of natural calcite minerals

    NASA Astrophysics Data System (ADS)

    Gunasekaran, S.; Anbalagan, G.

    2007-11-01

    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 calcite, 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 calcite 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.

  1. Calcite and dolomite in intrusive carbonatites. II. Trace-element variations

    NASA Astrophysics Data System (ADS)

    Chakhmouradian, Anton R.; Reguir, Ekaterina P.; Couëslan, Christopher; Yang, Panseok

    2015-06-01

    The composition of calcite 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 calcite and dolomite are controlled by crystal fractionation of fluorapatite, monazite and, possibly, other minerals. Enrichment in REE observed in some samples (up to ~2000 ppm in calcite) 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 calcite 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 crystal 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 calcite and dolomite, approach the average chondritic values. In consanguineous rocks, calcite invariably has higher REE and LILE levels than dolomite. Hydrothermal reworking of carbonatites does not produce a unique geochemical fingerprint, leading instead to a variety of evolutionary trends that range from light-REE and LILE enrichment (Turiy Mys, Russia) to heavy-REE enrichment and LILE depletion (Bear Lodge, USA). These differences clearly attest to variations in the chemistry of carbonatitic fluids and, consequently, their ability to mobilize specific trace elements from earlier-crystallized minerals. An important telltale indicator of hydrothermal reworking is deviation from the primary, chondrite-like REE ratios (in particular, Y/Ho and Eu/Eu*), accompanied by a variety of other compositional changes depending on the redox state of the fluid (e.g., depletion of carbonates in Mn owing to its oxidation and sequestration by secondary oxides). The effect of supergene processes was studied on a single sample from Bear Lodge, which shows extreme depletion in Mn and Ce (both due to oxidation), coupled with enrichment in Pb and U, possibly reflecting an increased availability of Pb2+ and (UO2)2+ species in the system. On the basis of these findings, several avenues for future research can be outlined: (1) structural mechanisms of REE uptake by carbonates; (2) partitioning of REE and LILE between cogenetic calcite and dolomite; (3) the effects of fluorapatite, phlogopite and pyrochlore fractionation on the LILE budget of magmatic carbonates; (4) the cause(s) of coupled Mn-Ce depletion in some primary calcite; and (5) relations between fluid chemistry and compositional changes in hydrothermal carbonates.

  2. Nano-structured calcite produced by micro-organisms in ancient and modern loess in Chinese Loess Plateau

    NASA Astrophysics Data System (ADS)

    Xu, H.; Chen, T.; Lu, H.; Wang, X.

    2005-12-01

    The results from transmission electron microscopy (TEM) and field emission gun scanning microscopy (FEG-SEM) investigation show that there are calcite nano-fibers (CNFs) formed during pedogenic process. The CNFs are widely distributed in the loess and red clay samples of Caoxian, Luochuan, Lingtai, Lantian, and Xifeng profiles as well as the samples of modern surface loess soils in Chinese Loess Plateau. Diameters of all the NFCs are about 40 nm, the length of the CNFs ranges from tens nanometer to several micrometers. Elongation direction of NFCs is unusual near parallel (105)* or (115)*. Crystals of NFCs arrange as bird net like and lattice-like frameworks. X-ray EDS spectra show the weak peaks of magnesium, phosphorous, and sulfur. Our investigation indicates that CNFs are in pore space of loess and paleosol and made up most of carbonate except for caliche nodular layers. Concentration of NFCs in the loess layers are significantly higher than those of paleosol layers because of leaching of carbonate in the paleosol forming environment (warn and wet paleoclimate). The "nanobacteria-like CNFs are well crystalline calcite single crystals with smoothes surfaces. The morphologies of CNFs are very unusual and different from the calcite single crystals observed in most geological environments. The CNFs are directly related to microbial activities in both ancient and modern loess. It is proposed that the intervention of organic compounds derived from microbial activities control the formation of the calcite nano-fibers. Both morphology and bulk composition of CNFs indicate that the formation of the CNFs involves bio-organics derived from microorganisms in loess deposit environment. Formation conditions of the calcite nano-fibers may information about paleoclimate, paleo-environment and paleoecology. So, the discovery of CNFs in loess-paloesol sequences can provide a new route for reconstruct paleoclimate by oxygen and carbon isotope from the CNFs.

  3. Dissolution of coccolithophorid calcite by microzooplankton and copepod grazing

    NASA Astrophysics Data System (ADS)

    Antia, A. N.; Suffrian, K.; Holste, L.; Müller, M. N.; Nejstgaard, J. C.; Simonelli, P.; Carotenuto, Y.; Putzeys, S.

    2008-01-01

    Independent of the ongoing acidification of surface seawater, the majority of the calcium carbonate produced in the pelagial is dissolved by natural processes above the lysocline. We investigate to what extent grazing and passage of coccolithophorids through the guts of copepods and the food vacuoles of microzooplankton contribute to calcite dissolution. In laboratory experiments where the coccolithophorid Emiliania huxleyi was fed to the rotifer Brachionus plicatilis, the heterotrophic flagellate Oxyrrhis marina and the copepod Acartia tonsa, calcite dissolution rates of 45-55%, 37-53% and 5-22% of ingested calcite were found. We ascribe higher loss rates in microzooplankton food vacuoles as compared to copepod guts to the strongly acidic digestion and the individual packaging of algal cells. In further experiments, specific rates of calcification and calcite dissolution were also measured in natural populations during the PeECE III mesocosm study under differing ambient pCO2 concentrations. Microzooplankton grazing accounted for between 27 and 70% of the dynamic calcite stock being lost per day, with no measurable effect of CO2 treatment. These measured calcite dissolution rates indicate that dissolution of calcite in the guts of microzooplankton and copepods can account for the calcite losses calculated for the global ocean using budget and model estimates.

  4. crystal

    NASA Astrophysics Data System (ADS)

    Bai, Fen; Wang, Qingpu; Tao, Xutang; Li, Ping; Zhang, Xingyu; Liu, Zhaojun; Shen, Hongbin; Lan, Weixia; Gao, Liang; Gao, Zeliang; Zhang, Junjie; Fang, Jiaxiong

    2014-08-01

    An eye-safe Raman laser is realized with BaTeMo2O9 (BTM) nonlinear crystal for the first time. By using a diode-end-pumped acousto-optically Q-switched Nd:YVO4 laser as the pumping source, the BTM crystal converts the fundamental laser at 1,342 nm to first-Stokes laser at 1,531 nm successfully. With an incident power of 10.8 W and a pulse repetition rate of 25 kHz, the average output power at 1,531 nm is obtained to be 0.83 W, corresponding to a diode-to-Stokes conversion efficiency of 7.7 %. The pulse width is 11 ns, and the peak power is 3.0 kW.

  5. Effect of fluid salinity on subcritical crack propagation in calcite

    NASA Astrophysics Data System (ADS)

    Rostom, Fatma; Røyne, Anja; Dysthe, Dag Kristian; Renard, François

    2013-01-01

    The slow propagation of cracks, also called subcritical crack growth, is a mechanism of fracturing responsible for a ductile deformation of rocks under crustal conditions. In the present study, the double-torsion technique was used to measure the effect of fluid chemistry on the slow propagation of cracks in calcite single crystals at room temperature. Time-lapse images and measurements of force and load-point displacement allowed accurate characterization of crack velocities in a range of 10- 8 to 10- 4 m/s. Velocity curves as a function of energy-release rates were obtained for different fluid compositions, varying NH4Cl and NaCl concentrations. Our results show the presence of a threshold in fluid composition, separating two regimes: weakening conditions where the crack propagation is favored, and strengthening conditions where crack propagation slows down. We suggest that electrostatic surface forces that modify the repulsion forces between the two surfaces of the crack may be responsible for this behavior.

  6. Numerical investigation of microbially induced calcite precipitation as leakage mitigation technology

    E-print Network

    Cirpka, Olaf Arie

    Numerical investigation of microbially induced calcite precipitation as leakage mitigation calcite precipitation (MICP). Other applications of MICP are discussed in [4]. Caprockfailure- ponent due to chemical reactions. Biofilm and calcite are immobile, hence the mass balance only yields

  7. The coordination of Mg in foraminiferal calcite. Supplementary Material Branson et al, 2013.

    E-print Network

    Cambridge, University of

    The coordination of Mg in foraminiferal calcite. Supplementary Material Branson et. al., 2013 to assess the coordination of Mg in foraminiferal calcite. We calcite, and the efficacy of the fitting algorithm used to assess

  8. Emission polarization study on quartz and calcite.

    NASA Technical Reports Server (NTRS)

    Vincent, R. K.

    1972-01-01

    Calculation of the spectral emission polarization of quartz and calcite 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.

  9. Bent crystal spectrometer for both frequency and wavenumber resolved x-ray scattering at a seeded free-electron laser

    SciTech Connect

    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

    2014-09-15

    We present a cylindrically curved GaAs x-ray spectrometer with energy resolution ?E/E = 1.1 ×?10{sup ?4} and wave-number resolution of ?k/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??m 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 seeded bandwidth of 1 eV and a significant range of wavenumbers must be covered in one exposure.

  10. Bent crystal spectrometer for both frequency and wavenumber resolved x-ray scattering at a seeded free-electron laser

    NASA Astrophysics Data System (ADS)

    Zastrau, Ulf; Fletcher, Luke B.; Förster, Eckhart; Galtier, Eric Ch.; Gamboa, Eliseo; Glenzer, Siegfried H.; Heimann, Philipp; Marschner, Heike; Nagler, Bob; Schropp, Andreas; Wehrhan, Ortrud; Lee, Hae Ja

    2014-09-01

    We present a cylindrically curved GaAs x-ray spectrometer with energy resolution ?E/E = 1.1 × 10-4 and wave-number resolution of ?k/k = 3 × 10-3, 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 ?m 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 seeded bandwidth of 1 eV and a significant range of wavenumbers must be covered in one exposure.

  11. Sr 2+/Ca 2+ and 44Ca/ 40Ca fractionation during inorganic calcite formation: II. Ca isotopes

    NASA Astrophysics Data System (ADS)

    Tang, Jianwu; Dietzel, Martin; Böhm, Florian; Köhler, Stephan J.; Eisenhauer, Anton

    2008-08-01

    Ca isotope fractionation during inorganic calcite formation was experimentally studied by spontaneous precipitation at various precipitation rates (1.8 < log R < 4.4 ?mol/m 2/h) and temperatures (5, 25, and 40 °C) with traces of Sr using the CO 2 diffusion technique. Results show that in analogy to Sr/Ca [see Tang J., Köhler S. J. and Dietzel M. (2008) Sr 2+/Ca 2+ and 44Ca/ 40Ca fractionation during inorganic calcite formation: I. Sr incorporation. Geochim. Cosmochim. Acta] the 44Ca/ 40Ca fractionation during calcite formation can be followed by the Surface Entrapment Model (SEMO). According to the SEMO calculations at isotopic equilibrium no fractionation occurs (i.e., the fractionation coefficient ?calcite-aq = ( 44Ca/ 40Ca) s/( 44Ca/ 40Ca) aq = 1 and ? 44/40Ca calcite-aq = 0‰), whereas at disequilibrium 44Ca is fractionated in a primary surface layer (i.e., the surface entrapment factor of 44Ca, F44Ca < 1). As a crystal grows at disequilibrium, the surface-depleted 44Ca is entrapped into the newly formed crystal lattice. 44Ca depletion in calcite can be counteracted by ion diffusion within the surface region. Our experimental results show elevated 44Ca fractionation in calcite grown at high precipitation rates due to limited time for Ca isotope re-equilibration by ion diffusion. Elevated temperature results in an increase of 44Ca ion diffusion and less 44Ca fractionation in the surface region. Thus, it is predicted from the SEMO that an increase in temperature results in less 44Ca fractionation and the impact of precipitation rate on 44Ca fractionation is reduced. A highly significant positive linear relationship between absolute 44Ca/ 40Ca fractionation and the apparent Sr distribution coefficient during calcite formation according to the equation ?Ca=(-1.90±0.26)·logD-2.83±0.28 is obtained from the experimental results at 5, 25, and 40 °C. Thus, Sr partitioning during calcite formation directly reflects Ca isotopic fractionation, independent of temperature, precipitation rate, and molar (Sr/Ca) aq ratio of the aqueous solution. If the (Sr/Ca) aq ratio is constant, ? 44/40Ca calcite-aq values can be directly followed by the Sr content of the precipitated calcite. A (Sr/Ca) aq ratio close to that of modern seawater yields the equation ?Ca=(-0.000940±0.000108)·Sr(mg/kgCaCO)-0.07±0.09. Our experimental results indicate that neither precipitation rate nor temperature dominantly controls Ca isotope fractionation. However, Ca isotopes and Sr content of inorganic calcite comprise an excellent environmental multi-proxy in natural and applied systems.

  12. Strain rate dependent calcite microfabric evolution - An experiment carried out by nature

    NASA Astrophysics Data System (ADS)

    Rogowitz, Anna; Grasemann, Bernhard; Huet, Benjamin; Habler, Gerlinde

    2014-12-01

    A flanking structure developed along a secondary shear zone in calcite marbles, on Syros (Cyclades, Greece), provides a natural laboratory for directly studying the effects of strain rate variations on calcite deformation at identical pressure and temperature conditions. The presence and rotation of a fracture during progressive deformation caused extreme variations in finite strain and strain rate, forming a localized ductile shear zone that shows different microstructures and textures. Textures and the degree of intracrystalline deformation were measured by electron backscattered diffraction. Marbles from the host rocks and the shear zone, which deformed at various strain rates, display crystal-preferred orientation, suggesting that the calcite preferentially deformed by intracrystalline-plastic deformation. Increasing strain rate results in a switch from subgrain rotation to bulging recrystallization in the dislocation-creep regime. With increasing strain rate, we observe in fine-grained (3 ?m) ultramylonitic zones a change in deformation regime from grain-size insensitive to grain-size sensitive. Paleowattmeter and the paleopiezometer suggest strain rates for the localized shear zone around 10-10 s-1 and for the marble host rock around 10-12 s-1. We conclude that varying natural strain rates can have a first-order effect on the microstructures and textures that developed under the same metamorphic conditions.

  13. Effect of calcite on lead-rich cementitious solid waste forms

    SciTech Connect

    Lee, Dongjin; Swarbrick, Gareth; Waite, T. David . E-mail: D.waite@unsw.edu.au

    2005-06-01

    The effect of calcite on lead-rich solidified waste forms generated using Portland cement has been investigated. Samples of cementitious wastes in the absence and presence of Pb and in the absence and presence of calcite were examined separately at 2, 7, 14 and 28 days of hydration by X-ray diffraction and SEM/EDS and for compressive strength. The presence of lead was observed to produce lead carbonate sulfate hydroxide (Pb{sub 4}SO{sub 4}(CO{sub 3}){sub 2}(OH){sub 2}), lead carbonate hydroxide hydrate (3PbCO{sub 3}.2Pb(OH){sub 2}.H{sub 2}O) and two other unidentified lead salts in cavity areas, and was observed to significantly retard the hydration of cement. Calcite addition to the Pb wastes was found to induce the rapid crystallization of calcium hydroxide coincident with the onset of C-S-H gel germination. The rapid dissolution of lead precipitates was observed with the subsequent development of very insoluble gel products of the form C-Pb-S-H. These products are formed by chemical incorporation of re-dissolved Pb species into silicate structures.

  14. Epitaxial high saturation magnetization FeN thin films on Fe(001) seeded GaAs(001) single crystal wafer using facing target sputterings

    SciTech Connect

    Ji Nian; Wu Yiming; Wang Jianping

    2011-04-01

    It was demonstrated that Fe-N martensite ({alpha}') films were grown epitaxially on Fe(001) seeded GaAs(001) single crystal wafer by using a facing target sputtering method. X-ray diffraction pattern implies an increasing c lattice constant as the N concentration increases in the films. Partially ordered Fe{sub 16}N{sub 2} films were synthesized after in situ post-annealing the as-sputtered samples with pure Fe{sub 8}N phase. Multiple characterization techniques including XRD, XRR, TEM, and AES were used to determine the sample structure. The saturation magnetization of films with pure Fe{sub 8}N phase measured by VSM was evaluated in the range of 2.0-2.2 T. The post annealed films show systematic and dramatic increase on the saturation magnetization, which possess an average value of 2.6 T. These observations support the existence of giant saturation magnetization in {alpha}''-Fe{sub 16}N{sub 2} phase that is consistent with a recent proposed cluster-atom model and the first principles calculation [N. Ji, X. Q. Liu, and J. P. Wang, New J. Phys. 12 063032 (2010)].

  15. Evaluation of defects generation in crystalline silicon ingot grown by cast technique with seed crystal for solar cells

    PubMed Central

    Tachibana, Tomihisa; Sameshima, Takashi; Kojima, Takuto; Arafune, Koji; Kakimoto, Koichi; Miyamura, Yoshiji; Harada, Hirofumi; Sekiguchi, Takashi; Ohshita, Yoshio; Ogura, Atsushi

    2012-01-01

    Although crystalline silicon is widely used as substrate material for solar cell, many defects occur during crystal 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

  16. Evaluation of defects generation in crystalline silicon ingot grown by cast technique with seed crystal for solar cells

    NASA Astrophysics Data System (ADS)

    Tachibana, Tomihisa; Sameshima, Takashi; Kojima, Takuto; Arafune, Koji; Kakimoto, Koichi; Miyamura, Yoshiji; Harada, Hirofumi; Sekiguchi, Takashi; Ohshita, Yoshio; Ogura, Atsushi

    2012-04-01

    Although crystalline silicon is widely used as substrate material for solar cell, many defects occur during crystal 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.

  17. Calcite Biomineralization by Bacterial Isolates from the Recently Discovered Pristine Karstic Herrenberg Cave

    PubMed Central

    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

    2012-01-01

    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. Calcite 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 calcite, vaterite, and monohydrocalcite. R. globerulus formed idiomorphous crystals with rhombohedral morphology, whereas A. sulfonivorans formed xenomorphous globular crystals, evidence for taxon-specific crystal 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

  18. Calcitization and silicification of evaporites in Guadalupian back-reef carbonates of the Delaware basin, west Texas and New Mexico

    SciTech Connect

    Ulmer, D.S.; Scholle, P.A. )

    1991-03-01

    Outcrop of the Seven Rivers, Yates, and Tansill formations contain numerous examples of evaporites that have been replaced by both quartz and calcite. The original evaporites consisted of discrete horizons, scattered nodules, enterolithic layers, and individual crystal 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. Calcite replacement followed silicification and consists of coarse, equant, blocky spar. Isotopic analyses of these calcites 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. Calcitization, however, was associated with mid-Tertiary block faulting that uplifted the area causing deep groundwater circulation. The isotopically very light calcites 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 calcites 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.

  19. Tectonic Evolution of Chingshui Geothermal Field Inferred from Evidence of Quartz and Calcite Veins

    NASA Astrophysics Data System (ADS)

    Lu, Y. C.; Song, S. R.; Wang, P. L.; Liu, C. M.; Yeh, E. C.

    2014-12-01

    The Chingshui geothermal field is located in the valley of Chingshui stream, where is about 27 km SW of Ilan, northeastern Taiwan. It is a tectonically complex area occurred by the Philippine Plate subducting beneath the Eurasian plate in the south with Okinawa Trough opening in the Ilan Plain. Owing to complicated geological structure, the heat source of Chingshui geothermal field is still controversial. For understanding hot fluid sources and tectonic evolution, this study focuses on field survey of veins and scaling in the Chingshui geothermal field, and the results inferred from the data of SEM, XRD, carbon and oxygen isotope, and Uranium-thorium dating. The Chingshui hot fluid contains both high concentrations of SiO­2 and HCO3-, therefore, temperature and pressure both drop when the hot fluids inject into shallower fractures, and calcite and quartz both could be precipitated with competition or simultaneously. In Chilukeng River, many euhedral quartz crystals occurred in large damage zone of Xioananao fault that indicated the temperature drop played the dominated role when the hot fluids injected into the shallow. It inferred that the quartz crystal precipitated under compression stress, evidenced by the Xioananao thrust fault with no surface rupture. Whiles, there are gouges in normal fault with abundant calcite or calcite with quartz veins cropped out in the confluence of Chingshui River and Chilukeng River. The results indicate that those veins occurred in more recent period by U-Th dating data, because of degassing CO2 occurred in open fractures by normal faulting or the stress changing from compression to extension. The standard oxygen isotopes range from 1.29 to 20.73 permil of SMOW and the clumped isotope of ?47 outcrop is 0.385 in calcite veins, suggest that the highest temperature of thermal fulids with calcite precipitations is 222?±9? by calibrated equation of Passey and Henkes 2012. Meanwhile, it also indicates that the oxygen isotope of initial water is 6.31 permil of SMOW which is totally different from the values of -5.36 and -6.5~-7.1 in the meteoric water of Chingshui area and the scaling of Well IC-13, respectively. This result infers that the compositions of hot fluids may be changed with different source in the Chingshui geothermal field.

  20. Chapter 9 Crystal Structure Although the symmetry and beauty of crystals have always excited curiosity and wonder, the

    E-print Network

    Lee, Ho Sung

    1-1 Chapter 9 Crystal Structure Although the symmetry and beauty of crystals have always excited by the fact that when he accidently dropped a crystal of calcite (a form of calcium carbonate), it fractured into smaller crystals that had the same interfacial angles between their plane surface as did the original

  1. High-pressure deformation of calcite marble and its transformation to aragonite under non-hydrostatic conditions

    USGS Publications Warehouse

    Hacker, B.R.; Kirby, S.H.

    1993-01-01

    We conducted deformation experiments on Carrara marble in the aragonite and calcite stability fields to observe the synkinematic transformation of calcite to aragonite, and to identify any relationships between transformation and deformation or sample strength. Deformation-induced microstructures in calcite crystals 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 calcite 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 calcite 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 crystals 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.

  2. High-pressure deformation of calcite marble and its transformation to aragonite under non-hydrostatic conditions

    NASA Astrophysics Data System (ADS)

    Hacker, Bradley R.; Kirby, Stephen H.

    1993-09-01

    We conducted deformation experiments on Carrara marble in the aragonite and calcite stability fields to observe the synkinematic transformation of calcite to aragonite, and to identify any relationships between transformation and deformation or sample strength. Deformation-induced microstructures in calcite crystals 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 calcite 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 calcite 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 crystals 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.

  3. Strontium Incorporation into Calcite Generated by Bacterial Ureolysis

    SciTech Connect

    Yoshiko Fujita; George D. Redden; Jani C. Ingram; Marnie M. Cortez; Robert W. Smith

    2004-08-01

    Strontium incorporation into calcite 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 calcite produced by ureolysis (0.5) were up to an order of magnitude higher than values reported in the literature for natural and synthetic calcites (0.02–0.4). They were also higher than values for calcite produced abiotically by ammonium carbonate addition (0.3). The precipitation of calcite 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 calcite samples as a solid solution. The extent of Sr incorporation appeared to be driven primarily by the overall rate of calcite 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 calcite precipitation, the application of this approach is promising for remediation of 90Sr contamination in environments where calcite is stable over the long term.

  4. Field Test of Combination Seeding Flares

    E-print Network

    Delene, David J.

    racks were loaded with a new type of flare manufactured by Ice Crystal Engineering. The new flaresField Test of Combination Seeding Flares Report to Ice Crystal Engineering 5985 49th St. SE 2008 during the Polarimetric Cloud Analysis and Seeding Test 2 (POLCAST2) field project. Aircraft

  5. Climate and cave control on Pleistocene/Holocene calcite-to-aragonite transitions in speleothems from Morocco: Elemental and isotopic evidence

    NASA Astrophysics Data System (ADS)

    Wassenburg, Jasper A.; Immenhauser, Adrian; Richter, Detlev K.; Jochum, Klaus Peter; Fietzke, Jan; Deininger, Michael; Goos, Manuela; Scholz, Denis; Sabaoui, Abdellah

    2012-09-01

    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 calcite. 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 calcite-to-aragonite transitions. Aragonite fabrics are well-preserved and represent primary features. In order to shed light on the factors that control alternating calcite 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 ?m resolution across stratigraphic and lateral transitions. Carbon and oxygen isotope ratios were analysed at 100 ?m resolution covering stratigraphic calcite-to-aragonite transitions. Results show that the precipitation of aragonite was driven by a decrease in effective rainfall, which enhanced prior calcite precipitation. Different geochemical patterns are observed between calcite 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 calcite precipitation in the limestone cave. A full understanding for the presence of lateral calcite-to-aragonite transitions is not reached. Trace elemental analysis, however, does suggest that different crystallographic parameters (ionic radius, amount of crystal defect sites, adsorption potential) may have a direct effect on the incorporation of Sr, Mg, Ba, Al, Ti, Th and possibly Y and P.

  6. Indications for the past redox environments in deep groundwaters from the isotopic composition of carbon and oxygen in fracture calcite, Olkiluoto, SW Finland.

    PubMed

    Sahlstedt, Elina; Karhu, Juha A; Pitkanen, Petteri

    2010-09-01

    In paleohydrogeological studies, the geochemical and isotope geochemical composition of fracture calcites can be utilised to gain information about the evolution of the composition of deep groundwaters in crystalline bedrock. The aim of our study was to investigate the latest hydrogeochemical evolution of groundwaters in the crystalline bedrock at Olkiluoto, which is the planned site for deep geological disposal of spent nuclear fuel. Samples were collected from drill cores intercepting water-conducting fractures at the upper ~500 m of the bedrock. The latest fracture calcite generations were identified using optical microscopy and electron microprobe. They occur as thin ~10-200 ?m crusts or small euhedral crystals on open fracture surfaces. These latest calcite fillings were carefully sampled and analysed for the isotopic composition on carbon and oxygen. In addition, fluid inclusion homogenisation temperatures were determined on selected calcite samples. Fluid inclusion data indicated a low temperature of formation for the latest fracture calcite fillings. The ?(18)O values of calcite in these fracture fillings vary only slightly, from-7.3 to-11.5 ‰ (Vienna Pee Dee Belemnite, VPDB), whereas the ?(13)C values fluctuate widely, from-30 to+31 ‰ (VPDB). The ?(13)C values of latest calcite fillings show a systematic pattern with depth, with high and variable ?(13)C values below 50 m. The high ?(13)C values indicate active methanogenesis during the formation of the latest calcite fillings. In contrast, the present-day methanic redox environment is restricted to depths below 200-300 m. It is possible that the shift in the redox environment at Olkiluoto has occurred during infiltration of SO2-(4)-rich marine waters, the latest of such events being the infiltration of brackish waters of the Littorina Sea stage of the Baltic Sea at ~8000-3000 BP. PMID:20665300

  7. Relative Shock Effects in Mixed Powders of Calcite, Gypsum, and Quartz: A Calibration Scheme from Shock Experiments

    NASA Technical Reports Server (NTRS)

    Bell, Mary S.

    2009-01-01

    The shock behavior of calcite 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 calcite yield seemingly conflicting results: early experimental devolatilization studies [7,8,9] suggested that calcite was substantially outgassed at 30 GPa (> 50%). However, the recent petrographic work of [10,11,12] presented evidence that essentially intact calcite 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 calcite, anhydrite, and gypsum, [14] observe calcite 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 crystallized 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 calcite and anhydrite shock wave experiments of [17] using improved equations of state of porous materials and vaporized products. They determined the pressures for incipient and complete vaporization to be 32.5 and 122 GPa for anhydrite and 17.8 and 54.1 GPa for calcite, respectively, a factor of 2 to 3 lower than reported earlier by [17].

  8. Vertical Distribution of Calcite at Yucca Mountain, Nevada, as an Indicator of Flow Through a Thick Unsaturated Zone

    SciTech Connect

    J.B. Paces; Z.E. Peterman

    2001-07-20

    Meteoric water percolating through 500 to 700 m of hydrologically unsaturated felsic tuffs provides a mechanism for release and transport of radionuclides from a potential high-level radioactive waste repository at Yucca Mountain, Nevada. Modern flow through the unsaturated zone (UZ) is low (probably <20 mm/year) and has not been observed directly. However, calcite formed from water percolating through fracture and lithophysal cavities over the last 12.8 million years provides, in part, a time-integrated record of UZ flow. Calcite concentration profiles were determined in dry-drilled boreholes USW WT-24 and USW SD-6 by acidifying samples of powdered rock cuttings collected over 5-foot intervals and measuring the evolved CO{sub 2} using gas chromatography. Resulting CO{sub 2}-derived calcite concentrations ranged from 30,800 to less than 20 ppm. Aliquots of the same powders also were analyzed for Ca, Ti, and Zr by energy-dispersive X-ray fluorescence. Concentrations of Ti and Zr in the crystal-poor, high-silica rhyolite parts of the Topopah Spring Tuff are uniform (standard deviations of 3 to 4%); however, Ca scatters widely (standard deviations of 21 and 32%). Concentrations of Ca are positively correlated to CO{sub 2}-derived calcite concentrations and regressions for samples of the two major rhyolitic tuffs yielded r{sup 2} values >0.9, CO{sub 2}-intercept Ca concentrations in the range of values determined on fresh rock samples, and slopes equivalent to addition of stoichiometric calcite. Therefore, combined CO{sub 2} and Ca data provide a means of determining the amount of secondary calcite added to the rock mass from percolating water. The vertical distribution of calcite is related to lithostratigraphy with the largest concentrations in the welded hydrogeologic unit of the Tiva Canyon Tuff near the land surface and progressively smaller values with depth into the underlying nonwelded units. Large values also may be present in the upper parts of the underlying welded hydrogeologic unit of the Topopah Spring Tuff, but generally decrease in the deeper parts of the unit. The spatial distribution of calcite is complex and likely is related, in part, to spatial variations in the amount of water and vapor transported through the thick UZ.

  9. Magnesium inhibition of calcite dissolution kinetics

    SciTech Connect

    Arvidson, Rolf S.; Collier, Martin; Davis, Kevin J.; Vinson, Michael D.; Amonette, James E.; Luttge, Andreas

    2006-02-01

    We present evidence of inhibition of calcite 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.

  10. Paleoclimatic and paleohydrologic records from secondary calcite: Yucca Mountain, Nevada

    SciTech Connect

    Whelan, J.F.; Stuckless, J.S.; Moscati, R.J.; Vaniman, D.T.

    1994-12-31

    Stable isotope analyses of calcite and opal, fluid inclusion formation conditions and gas compositions, Sr isotope ratios, and REE compositions all support formation of secondary calcite 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 calcite 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 calcite 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.

  11. Kinetics and Mechanisms of Calcite Reactions with Saline Waters

    SciTech Connect

    Chapman, Piers; *Morse, John W.

    2010-11-15

    1. Objective The general objective of this research was to determine the kinetics and mechanisms of calcite 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 calcite surface morphology and composition would be made to provide an understanding of rate controlling mechanisms.

  12. Magnesium content of calcite in carapaces of benthic armine Ostracoda

    E-print Network

    Cadot, H. M.; Kaesler, R. L.

    1977-07-22

    PALEONTOLOGICAL CONTRIBUTIONS July 22, 1977 Paper 87 MAGNESIUM CONTENT OF CALCITE IN CARAPACES OF BENTHIC MARINE OSTRACODA 1 H. MEADE CADOT, JR.,2 and ROGER L. KAESLER3 2 Antioch College—New England and The Harris Center for Conservation Education, Hancock, New... Hampshire; 'The University of Kansas, Lawrence ABSTRACT Statistically significant differences in mean magnesium content of calcite in carapaces of benthic marine Ostracoda were found to occur among four superfamily groups and among regions of the carapace...

  13. Biogenic and synthetic high magnesium calcite A review q Xia Long, Yurong Ma

    E-print Network

    Qi, Limin

    Review Biogenic and synthetic high magnesium calcite ­ A review q Xia Long, Yurong Ma , Limin Qi e i n f o Article history: Available online 26 November 2013 Keywords: High-Mg calcite Biominerals-Mg calcites in different marine organisms were summarized in detail in this review. The high-Mg calcites

  14. O of cellulose organic fraction combined with 18 O of calcite and 18

    E-print Network

    Edwards, Thomas W.D.

    1 18 O of cellulose organic fraction combined with 18 O of calcite and 18 O of diatoms in lake of authigenic calcite and 18 O of diatoms (if available). The results of 18 O of authigenic calcite, diatom and cellulose are presented in Fig.3. Fig. 3. Oxygen isotopic composition of authigenic calcite, diatom

  15. The calcite !! aragonite transformation in low-Mg marble: Equilibrium relations, transformation mechanisms, and rates

    E-print Network

    Hacker, Bradley R.

    The calcite !! aragonite transformation in low-Mg marble: Equilibrium relations, transformation] Experimental transformation of a rather pure natural calcite marble to aragonite marble did not proceed via calcite grains, producing Mg-rich calcite rods that persisted as relicts. Nucleation of aragonite occurred

  16. Nickel sorption on calcite surface: a macroscopic experimental study Thais R. LAMANA

    E-print Network

    Nickel sorption on calcite surface: a macroscopic experimental study By Thais R. LAMANA Department. calcite, oxides), and of the adsorption behaviour of divalent metal ions on calcite as well carried out to characterize the adsorption behaviour of Ni on calcite under controlled laboratory

  17. A novel determination of calcite dissolution kinetics in seawater

    NASA Astrophysics Data System (ADS)

    Subhas, Adam V.; Rollins, Nick E.; Berelson, William M.; Dong, Sijia; Erez, Jonathan; Adkins, Jess F.

    2015-12-01

    We present a novel determination of the dissolution kinetics of inorganic calcite in seawater. We dissolved 13 C -labeled calcite in unlabeled seawater, and traced the evolving ?13 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 calcite 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 (?) of: This result substantiates the non-linear response of calcite 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 calcite-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 calcite lysocline.

  18. The differnces between bond lengths in biogenic and geologocal calcite.

    SciTech Connect

    Zlotoyabko, E.; Caspi, E. N.; Fieramosca, J. S.; Von Dreele, R. B.; Marin, F.; Mor, G.; Politi, Y.; Addadi, L.; Weiner, S.

    2010-01-01

    We used high-resolution neutron powder diffraction to accurately measure the atomic positions and bond lengths in biogenic and geological calcite. 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 calcite we found some atomic bonds to have significantly different lengths as compared to those in geological calcite, 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 calcite (as compared to geological calcite) 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 calcite as compared to geological samples was detected. Possible explanations for the experimental findings are discussed.

  19. Calcite Farming at Hollow Ridge Cave: Calibrating Net Rainfall and Cave Microclimate to Dripwater and Calcite Chemical Variability

    NASA Astrophysics Data System (ADS)

    Tremaine, D. M.; Kilgore, B. P.; Froelich, P. N.

    2012-04-01

    Stable isotope (?18O and ?13C) and trace element records in cave speleothems are often interpreted as climate changes in rainfall amount or source, cave air temperature, overlying vegetation and atmospheric pCO2. However, these records are difficult to verify without in situ calibration of changes in cave microclimate (e.g., net rainfall, interior ventilation changes) to contemporaneous variations in dripwater and speleothem chemistry. In this study at Hollow Ridge Cave (HRC) in Marianna, Florida (USA), cave dripwater, bedrock, and modern calcite (farmed in situ) were collected in conjunction with continuous cave air pCO2, temperature, barometric pressure, relative humidity, radon-222 activity, airflow velocity and direction, rainfall amount, and drip rate data [1]. We analyzed rain and dripwater ?D and ?18O, dripwater Ca2+, pH, ?13C and TCO2, cave air pCO2 and ?13C, and farmed calcite ?18O and ?13C to examine the relationships among rainwater isotopic composition, cave air ventilation, cave air temperature, calcite growth rate and seasonal timing, and calcite isotopic composition. Farmed calcite ?13C decreases linearly with distance from the front entrance to the interior of the cave during all seasons, with a maximum entrance-to-interior gradient of ??13C = -7‰ . A whole-cave "Hendy test" at distributed contemporaneous farming sites reveals that ventilation induces a +1.9 ± 0.96‰ ?13C offset between calcite precipitated in a ventilation flow path and out of flow paths. Farmed calcite ?18O exhibits a +0.82 ± 0.24‰ offset from values predicted by both theoretical calcite-water calculations and by laboratory-grown calcite [2]. Unlike calcite ?13C, oxygen isotopes show no ventilation effects and are a function only of temperature. Combining our data with other speleothem studies, we find a new empirical relationship for cave-specific water-calcite oxygen isotope fractionation across a range of temperatures and cave environments: 1000 ln ? = 16.1(1000/T) - 24.6 We analyzed anions, cations, and trace elements in dripwater, bedrock, and farmed calcite to examine the relationships between net rainfall, drip rates, drip water chemistry, and calcite chemistry. Dripwater Mg/Ca and Sr/Ca ratios fall on coherent mixing lines between three geochemical endmembers: rainwater, dissolved dolomite, and dissolved limestone. Dripwater Sr/Ca vs. Mg/Ca ratios are also influenced by evaporative enrichment within the epikarst as a function of net rainfall amount [3]. Farmed calcite trace Cation/Ca ratios faithfully track short-term seasonal variations in dripwater chemistry for Na, Mg, Sr, Ba and U. However, speleothem calibrations are unique to each drip site regardless of proximity to one another, suggesting that individual speleothems are unlikely to be useful as a whole-cave hydrologic proxy. [1] Kowalczk, A. J., Froelich, P. N., 2010. Cave air ventilation and CO2 outgassing by radon-222 modeling: How fast do caves breathe? Earth & Planet. Sci. Lett. 289, 209-219. [2] Tremaine, D. M., Froelich, P. N., Wang, Y., 2011. Speleothem calcite farmed in situ: Modern calibration of ?18O and ?13C paleoclimate proxies in a continuously-monitored natural cave system. Geochim. Cosmochim. Acta 75, 4929-4950. [3] Tremaine, D. M., Froelich, P. N., 2012. Speleothem trace element signatures: A modern hydrologic geochemical study of cave drip waters and farmed calcite. Geochim. Cosmochim. Acta (submitted)

  20. Photoinduced synthesis of single-digit micrometer-size spheroidal calcite composites in the presence of partially hydrolyzed poly(vinyl alcohol)

    NASA Astrophysics Data System (ADS)

    Nishio, Takashi; Naka, Kensuke

    2015-06-01

    Photoinduced crystallization 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, calcite spheroids in single-digit micrometer-sizes were obtained as major products at pH 8.4. The obtained calcite 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 crystallization of both vaterite and calcite 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 crystal growth in the presence of PVAPS seemed to enable the formation of the spheroidal composites of calcite in single-digit micrometer-sizes.

  1. Effect of Otoconial Proteins Fetuin A, Osteopontin, and Otoconin 90 on the Nucleation and Growth of Calcite

    PubMed Central

    2015-01-01

    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 calcite 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 crystal morphology. All three proteins were found to be potent inhibitors of calcite 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 calcite nucleation on films of these proteins adsorbed onto mica surfaces. By measuring the calcite 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 calcite 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

  2. The Raman spectrum of CaCO{sub 3} polymorphs calcite and aragonite: A combined experimental and computational study

    SciTech Connect

    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

    2014-04-28

    Powder and single crystal 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 calcite 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 calcite 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 calcite and aragonite in the case of powder spectra, and among different polarization directions of each compound in the case of single crystal spectra.

  3. Polysaccharide chemistry regulates kinetics of calcite nucleation through competition of interfacial energies

    PubMed Central

    Hamm, Laura M.; Han, Nizhou; De Yoreo, James J.; Dove, Patricia M.

    2013-01-01

    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 calcite 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–crystal and substrate–liquid interfacial energies. Chitosan presents a low-energy barrier to nucleation because its near-neutral charge favors formation of a substrate–crystal 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–crystal interfaces. The findings support a directing role for PS in biomineral formation and demonstrate that substrate–crystal interactions are one end-member in a larger continuum of competing forces that regulate heterogeneous crystal nucleation. PMID:23690577

  4. Surface kinetic model for isotopic and trace element fractionation during precipitation of calcite from aqueous solution

    SciTech Connect

    DePaolo, D.

    2010-10-15

    A surface reaction kinetic model is developed for predicting Ca isotope fractionation and metal/Ca ratios of calcite 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 crystal 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 calcite (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 calcite 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 calcite precipitation. Mechanistic models for calcite 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}. Allowing R{sub b} to vary as R{sub p}{sup 1/2}, consistent with available precipitation rate studies, produces a better fit to some trace element and isotopic data than a model where R{sub b} is constant. This model can account for most of the experimental data in the literature on the dependence of {sup 44}Ca/{sup 40}Ca and metal/Ca fractionation in calcite as a function of precipitation rate and temperature, and also accounts for {sup 18}O/{sup 16}O variations with some assumptions. The apparent temperature dependence of Ca isotope fractionation in calcite may stem from the dependence of R{sub b} on temperature; there should be analogous pH dependence at pH < 6. The proposed model may be valuable for predicting the behavior of isotopic and trace element fractionation for a range of elements of interest in low-temperature aqueous geochemistry. The theory presented is based on measureable thermo-kinetic parameters in contrast to models that equire hyper-fast diffusivity in near-surface layers of the solid.

  5. Surface kinetic model for isotopic and trace element fractionation during precipitation of calcite from aqueous solution

    SciTech Connect

    DePaolo, Donald J.

    2011-01-01

    A surface reaction kinetic model is developed for predicting Ca isotope fractionation and metal/Ca ratios of calcite 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 (Rp) to the gross forward precipitation rate (Rf), for conditions where ionic transport to the growing crystal surface is not rate-limiting. The value of Rp has been experimentally measured under varying conditions, but the magnitude of Rf 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, Rf can be estimated from the bulk far-from-equilibrium dissolution rate of calcite (Rb or kb), since at equilibrium Rf = Rb, and Rp = 0. Hence it can be inferred that Rf ? Rp + Rb. The dissolution rate of pure calcite is measureable and is known to be a function of temperature and pH. At given temperature and pH, equilibrium precipitation is approached when Rp (=Rf - Rb) « Rb. For precipitation rates high enough that Rp » Rb, 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 Rp ? Rb for Ca isotopic fractionation. According to this model, Ca isotopic data can be used to estimate Rf for calcite precipitation. Mechanistic models for calcite 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 Rp. Allowing Rb to vary as Rp1/2, consistent with available precipitation rate studies, produces a better fit to some trace element and isotopic data than a model where Rb is constant. This model can account for most of the experimental data in the literature on the dependence of 44Ca/40Ca and metal/Ca fractionation in calcite as a function of precipitation rate and temperature, and also accounts for 18O/16O variations with some assumptions. The apparent temperature dependence of Ca isotope fractionation in calcite may stem from the dependence of Rb on temperature; there should be analogous pH dependence at pH < 6. The proposed model may be valuable for predicting the behavior of isotopic and trace element fractionation for a range of elements of interest in low-temperature aqueous geochemistry. The theory presented is based on measureable thermo-kinetic parameters in contrast to models that require hyper-fast diffusivity in near-surface layers of the solid.

  6. Seed proteomics

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Seeds comprise a protective covering, a small embryonic plant, and a nutrient-storage organ. Seeds are protein-rich, and have been the subject of many mass spectrometry-based analyses. Seed storage proteins (SSP), which are transient depots for reduced nitrogen, have been studied for decades by cel...

  7. Seed Proteomics"

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Proteomic analysis of seeds encounters some specific problems that do not impinge on analyses of other plant cells, tissues, or organs. There are anatomic considerations. Seeds comprise the seed coat, the storage organ(s), and the embryonic axis. Are these to be studied individually or as a compo...

  8. Sequestration of selenium on calcite surfaces revealed by nanoscale imaging

    NASA Astrophysics Data System (ADS)

    Putnis, Christine V.; Renard, François; King, Helen E.; Montes-Hernandez, German; Ruiz-Agudo, Encarnacion

    2014-05-01

    Selenium is an important element because of its high toxicity in natural systems. In-situ atomic force microscopy observations of calcite surfaces during contact with selenium-bearing solutions demonstrate that selenium trapping can occur under conditions in which calcite both dissolves and precipitates. The contact of solutions containing selenium in two states of oxidation (either Se(IV ) or Se(V I)) onto a growing or dissolving calcite surface either changes the growth pattern or results in precipitates formed during dissolution. In the form of selenite (Se(IV )), but not as selenate (Se(IV )), selenium can be incorporated into calcite during growth. During dissolution, in the presence of selenate (Se(V I)), the precipitates formed remained small during the observation period. When injecting selenite (Se(IV )), the precipitates grew significantly, and were identified as CaSeO3·H2O, based on SEM observations, Raman spectroscopy and thermodynamic calculations. An interpretation is proposed where dissolution of calcite increases the calcium concentration in a thin boundary layer in contact with the surface, allowing the precipitation of a selenium phase. This process of dissolution-precipitation provides a new mechanism for selenium sequestration and extends the range of thermodynamic conditions under which such a process is efficient.

  9. A Raman spectroscopic comparison of calcite and dolomite.

    PubMed

    Sun, Junmin; Wu, Zeguang; Cheng, Hongfei; Zhang, Zhanjun; Frost, Ray L

    2014-01-01

    Raman spectroscopy was used to characterize and differentiate the two minerals calcite 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 calcite and dolomite were observed at 1440, 1088, 715 and 278 cm(-1). The significant differences between the minerals calcite and dolomite are observed by Raman spectroscopy. Calcite 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. Calcite 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. PMID:23988531

  10. A Raman spectroscopic comparison of calcite and dolomite

    NASA Astrophysics Data System (ADS)

    Sun, Junmin; Wu, Zeguang; Cheng, Hongfei; Zhang, Zhanjun; Frost, Ray L.

    2014-01-01

    Raman spectroscopy was used to characterize and differentiate the two minerals calcite 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 calcite and dolomite were observed at 1440, 1088, 715 and 278 cm-1. The significant differences between the minerals calcite and dolomite are observed by Raman spectroscopy. Calcite 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. Calcite 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.

  11. Geochronological Potential of Isoleucine Epimerization in Calcite Speleothems

    NASA Astrophysics Data System (ADS)

    Lauritzen, Stein-Erik; Erik Haugen, John; Løvlie, Reidar; Gilje-Nielsen, Helge

    1994-01-01

    The extent of isoleucine epimerization in a calcite speleothem was determined to evaluate the amino acid racemization method in abiotic calcite. A 5.5-cm-thick flowstone slab from Hamarnesgrotta, northern Norway, was analyzed for amino acid concentration, composition, and isoleucine epimerization at 26 levels through the sequence. U-series dates provide an independent chronologic control. Epimerization increases monotonically with stratigraphic depth and linearily with U-series age, independent of amino acid concentrations. The rate of epimerization is calibrated against the U-series dates, and extrapolation into lower strata beyond the U-series limit yields absolute age estimates that are consistent with paleomagnetic data from the same speleothem. The results suggest that, if adequately calibrated, amino acid dating is applicable to speleothem material reaching time spans beyond the range of conventional dating methods. Amino acids in the speleothem were probably derived from surface soils and are associated with brown humic stains in the calcite.

  12. Structure and properties of Bi(Zn0.5Ti0.5)O3- Pb(Zr(1-x)Ti(x))O3 ferroelectric single crystals grown by a top-seeded solution growth technique.

    PubMed

    Wang, Bixia; Wu, Xiaoqing; Ren, Wei; Ye, Zuo-Guang

    2015-06-01

    Bi(Zn0.5Ti0.5)O3 (BZT)-modified Pb(Zr(1-x)Ti(x))O3 (PZT) single crystals have been grown using a top-seeded solution growth technique and characterized by various methods. The crystal structure is found to be rhombohedral by means of X-ray powder diffraction. The composition and homogeneity of the as-grown single crystals 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 crystals are enhanced by the BZT substitution with a remanent polarization of 28 ?C/cm(2) and a coercive field E(C) of 22.1 kV/cm. PMID:26067036

  13. Microbially Induced Calcite Precipitation for Subsurface Immobilization of Contaminants

    NASA Astrophysics Data System (ADS)

    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.

    2011-12-01

    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 calcite. We have found that calcite precipitation and co-precipitation of Sr can be accelerated by the activity of urea hydrolyzing microorganisms, that higher calcite precipitation rates can result in increased Sr partitioning, and that nutrient additions can stimulate ureolytic activity. To extend our understanding of microbially induced calcite 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 calcite 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 calcite precipitation. Modeling activities are underway to define field-scale urea hydrolysis rates.

  14. Discovery of a Cretaceous Scleractinian Coral with a Calcitic Skeleton

    NASA Astrophysics Data System (ADS)

    Stolarski, J.; Meibom, A.; Przenioslo, R.; Mazur, M.

    2007-12-01

    It has been generally thought that scleractinian corals form purely aragonitic skeletons. We show that a well- preserved fossil coral, Coelosmilia sp. from the Upper Cretaceous (ca. 70 Ma), has preserved skeletal structural features identical to those observed in present day scleractinians. However, the skeleton of Coelosmilia sp. is entirely calcitic. Its fine-scale structure and chemistry indicate that the calcite is primary and did not from via diagenetic alteration of aragonite. This result implies that corals, like other groups of marine, calcium carbonate- producing organisms, can form skeletons of different carbonate polymorphs. Implications for coral biomineralization and evolution will be discussed.

  15. Chalk-calcite-microfluidic experiments: construction and flooding of microsystems with reactive fluids

    NASA Astrophysics Data System (ADS)

    Neuville, Amélie; Thuy Luu, Thi; Dysthe, Dag Kristian; Vinningland, Jan Ludvig; Hiorth, Aksel

    2015-04-01

    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 calcite crystals. 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 calcite, we obtain reactive rates that are coherent with the litterature and with numerical simulations based on Lattice-Boltzmann methods.

  16. Field test of a calcite dissolution rate law: Fort's Funnel Cave, Mammoth Cave National Park

    SciTech Connect

    Slunder, J.S. ); Groves, C.G. . Center for Cave and Karst Studies)

    1994-03-01

    The laboratory-derived calcite 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 crystal 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 calcite, as were the waters within this part of the groundwater flow system.

  17. Inversion of calcite twin data for stress (2) : EBSD as a tool for data measurements

    NASA Astrophysics Data System (ADS)

    Parlangeau, Camille; Lacombe, Olivier; Brisset, Francois; Kohler, Eric; Daniel, Jean-Marc; Schueller, Sylvie

    2015-04-01

    Inversion of calcite 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 calcite-twin orientations that should be fast, without any loss of information, and which must reconcile (1) the need for a large amount of calcite twin data (3 mutually perpendicular thin sections and at least 30 crystals 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 calcite 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 and its coordinates entered in a file later used to pilot automatically the EBSD spot. This new procedure is applied on sections from natural samples; the EBSD data are converted and restored into the geographical framework and analyzed using the improved Etchecopar stress inversion technique. The results are compared to the results obtained from classical, optically-based measurements of the same sections using the Universal-stage. The advantages and limitations of this approach are discussed.

  18. Shock Waves Trigger Fault Weakening in Calcite-bearing Rocks During Earthquakes

    NASA Astrophysics Data System (ADS)

    Spagnuolo, E.; Plumper, O.; Violay, M.; Cavallo, A.; Di Toro, G.

    2014-12-01

    The weakening mechanism of calcite-bearing rocks is still poorly understood though many major earthquakes stroke within carbonate sequences. Insights derive from the laboratory: in experiments performed on calcite-bearing gouges, up to 90% drop in friction is associated to grain size reduction to the nanoscale and the formation of crystal-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. calcite 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 origin of such a shock-like behaviour responsible for large initial frictional weakening. The passage of the shock wave induces pervasive nanofracturing with grain size reduction to the nano-scale and an abrupt temperature rise responsible for calcite decarbonation and formation of carbon amorphous material.

  19. Petrology of UHP calcite marble from the Kokchetav Massif

    NASA Astrophysics Data System (ADS)

    Aoki, K.; Adachi, T.; Kikuchi, M.; Ogasawara, Y.

    2004-12-01

    In the Kumdy-kol area, Kokchetav Massif, northern Kazakhstan, three types of UHP marbles have been described: diamond-bearing dolomite marble, Ti-clinohumite-bearing dolomitic marble (Ogasawara et al., 2000) and titanite-bearing calcite marble (Ogasawara et al., 2002). UHP calcite marble is distinguished from other types of UHP marbles by pure calcite (after aragonite) as a dominant carbonate phase. This calcite marble has unique evidence of UHP metamorphism; titanite with coesite exsolution and its precursor compositions indicated that the peak P-T conditions was > 6 GPa and 980-1250 C (Ogasawara et al., 2000; 2002). This rock shows typical granoblastic texture consisting of calcite, diopside, K-feldspar, titanite and symplectite (diopside + zoisite) after garnet. The peak assemblage was aragonite + diopside + K-feldspar + garnet + titanite. Based on the phase relations in the system CaO-MgO-TiO2-SiO2-CO2-H2O, aragonite + diopside + rutile tie-triangle is stable under UHP conditions and divides the compositional space into dolomite-bearing or dolomite-free tetrahedrons (Kikuchi et al., 2003). The presence of titanite in calcite marble means that P-T condition was located at the right-hand side of the reaction rutile + aragonite + coesite = titanite + CO2. Previously described titanite-bearing calcite marble is diamond-free (A-type) and is characterized by titanite with coesite exsolution (Ogasawara et al., 2002). Recently, we found a small amount of diamond in calcite marble (B-type) that is characterized by microdiamond in diopside, and by the lack of K-feldspar and low amount of titanite. No diamond occurs in titanite. Rutile, aragonite and calcite inclusions in titanite were found in titanite of B-type calcite marble. These three inclusion phases in titanite that were confirmed by laser Raman spectroscopy are the evidence for titanite formation reaction described above. This titanite forming reaction occurs at extremely low XCO2 conditions as 0.02. In B-type calcite marble, microdiamond occurs locally and its amount is low; only 61 grains were found in two thin sections. Distributions of titanite, K-feldspar and diamond are heterogeneous and seem to form layers. Diamond occurs in the domain where amounts of titanite and K-feldspar are relatively low. Low amount of microdiamond may be related with extremely low-XCO2 condition under UHP metamorphism. References Ishida et al. (2003: Journal of Metamorphic Geology, Vol. 21, p. 515-522. Kikuchi et al. (2003): EOS Transactions AGU, Vol. 84, F1532. Ogasawara et al. (2000): The Island Arc, Vol. 9, p 400-416. Ogasawara et al. (2002): American Mineralogist, Vol. 87, p. 454-461.

  20. The inhibition of calcium carbonate crystal growth by the cysteine-rich Mdm2 peptide.

    PubMed

    Dalas, E; Chalias, A; Gatos, D; Barlos, K

    2006-08-15

    The crystal growth of calcite, 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. Crystallization took place exclusively on well-characterized calcite crystals 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 crystal growth of calcite by 22-58% in the concentration range tested, through adsorption onto the active growth sites of the calcite crystal 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. PMID:16678843

  1. Aragonite, breunnerite, calcite and dolomite in the CM carbonaceous chondrites: High fidelity recorders of progressive parent body aqueous alteration

    NASA Astrophysics Data System (ADS)

    Lee, Martin R.; Lindgren, Paula; Sofe, Mahmood R.

    2014-11-01

    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 calcite, whereas aragonite occurs only in the CM2.5-CM2.2 meteorites and dolomite in the CM2.2-CM2.0. All of the aragonite crystals, and most of the calcite 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 crystals 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 crystals and the proportion of them that have preserved crystal 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 calcite. Following completion of cementation, the carbonates were partially replaced by phyllosilicates and sulphides. Calcite 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 calcite were replaced by Fe-rich serpentine and Fe-Ni sulphide, again followed by Mg-rich serpentine. The difference between meteorites in the mineralogy of their replacive sulphides may again reflect greater temperatures in the parent body regions from where the more highly altered CMs were derived. This transition from Fe-rich to Mg-rich carbonate replacement products mirrors the chemical evolution of parent body solutions in response to consumption of Fe-rich primary minerals followed by the more resistant Mg-rich anhydrous silicates. Almost all of the CMs examined contain a second generation of calcite that formed after the sulphides and phyllosilicates and by replacement of remaining anhydrous silicates and dolomite (dedolomitization). The Ca and CO2 required for this replacive calcite is likely to have been sourced by dissolution of earlier formed carbonates, and ions may have been transported over metre-plus distances through high permeability conduits that were created by impact fracturing.

  2. Seeding Rangeland. 

    E-print Network

    Welch, Tommy G.; Haferkamp, Marshall R.

    1987-01-01

    years on land barren from farming. On other bare areas, such as newly constructed dams and newly laid pipelines, seeding to establish a plant cover often is necessary to prevent wind and water erosion WHERE TO SEED Seed only those sites having..., expend the most effort on ones with the best chance for success. Select seeding sites so the area can be incorporated into the overall ranch management. Sites with sufficient soil depth for adequate root development and water storage or sites that can...

  3. Isolation and identification of Pseudomonas azotoformans for induced calcite precipitation.

    PubMed

    Heidari Nonakaran, Siamak; Pazhouhandeh, Maghsoud; Keyvani, Abdullah; Abdollahipour, Fatemeh Zahra; Shirzad, Akbar

    2015-12-01

    Biomineralization is a process by which living organisms produce minerals. The extracellular production of these biominerals by microbes has potential for various bioengineering applications. For example, crack remediation and improvement of durability of concrete is an important goal for engineers and biomineral-producing microbes could be a useful tool in achieving this goal. Here we report the isolation, biochemical characterization and molecular identification of Pseudomonas azotoformans, a microbe that produces calcite and which potentially be used to repair cracks in concrete structures. Initially, 38 bacterial isolates were isolated from soil and cements. As a first test, the isolates were screened using a urease assay followed by biochemical tests for the rate of urea hydrolysis, calcite production and the insolubility of calcite. Molecular amplification and sequencing of a 16S rRNA fragment of selected isolates permitted us to identify P. azotoformans as a good candidate for preparation of biotechnological concrete. This species was isolated from soil and the results show that among the tested isolates it had the highest rate of urea hydrolysis, produced the highest amount of calcite, which, furthermore was the most adhesive and insoluble. This species is thus of interest as an agent with the potential ability to repair cracks in concrete. PMID:26386580

  4. Utricular otoconia of some amphibians have calcitic morphology

    NASA Technical Reports Server (NTRS)

    Pote, K. G.; Ross, M. D.

    1993-01-01

    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 calcite, rather than the widely accepted idea that they are mineralized by calcium carbonate of the aragonite polymorph.

  5. The coordination and distribution of B in foraminiferal calcite

    E-print Network

    Branson, Oscar; Kaczmarek, Karina; Redfern, Simon A.T.; Misra, Sambuddha; Langer, Gerald; Tyliszczak, Tolek; Bijma, Jelle; Elderfield, Henry

    2015-02-25

    The isotopic ratio and concentration of B in foraminiferal calcite appear to reflect the pH and bicarbonate concentration of seawater. The use of B as a chemical proxy tracer has the potential to transform our understanding of the global carbon...

  6. On the Shock Behavior of Calcite: Recent Results from MEMIN Experiments

    NASA Astrophysics Data System (ADS)

    Hamann, C.; Hecht, L.; Deutsch, A.

    2015-09-01

    Hypervelocity impact and laser melting experiments, aiming at a better understanding of the shock behavior of calcite, suggest that both melting and decomposition of calcite can occur at P–T conditions commensurate with impact processes.

  7. Modelling of the thermal dependence of structural and elastic properties of calcite, CaCO3

    NASA Astrophysics Data System (ADS)

    Pavese, A.; Catti, M.; Parker, S. C.; Wall, A.

    1996-03-01

    A computational method, based on the quasiharmonic approximation, has been computer-coded to calculate the temperature dependence of elastic constants and structural features of crystals. The model is applied to calcite, CaCO3; an interatomic potential based on a C-O Morse function and Ca-O and O-O Borntype interactions, including a shell model for O, has been used. Equilibrations in the range 300 800 K reproduce the experimental unit-cell edges and bond lengths within 1%. The simulated thermal expansion coefficients are 22.3 (//c) and 2.6 (? c), against 25.5 and-3.7×10-6K-1 experimental values, respectively. The thermal coefficients of elastic constants tend to be underestimated; for the bulk modulus, -2.3 against-3.7×10-4K-1 is obtained.

  8. Crystal-like growth of a metal oxide/CNT composite fiber with electroplated "seed" from a CNT-dispersed nonaqueous electrolyte.

    PubMed

    Kim, Wal Jun; Jang, Eui Yun; Seo, Dong Kyun; Kang, Tae June; Jin, Kyoung Cheol; Jeong, Dae Hong; Kim, Yong Hyup

    2010-10-19

    A fabrication technique is developed for the preparation of metal oxide/CNT composites. An essential feature of the technique lies in the use of nonaqueous electrolyte in place of the usual aqueous electrolyte, which ensures well-dispersed CNTs without surfactants. After a "seed" is formed by electroplating on the anode, the seed is simply pulled up at a certain speed to grow a 1D CNT composite structure. The technique leads to a uniform distribution of metal oxide and a high weight fraction of CNT in the composite structure. Moreover, the conductivity of the composite is much higher than that of the CNT fibers fabricated with polymer. PMID:20843050

  9. Stability of Basalt plus Anhydrite plus Calcite at HP-HT: Implications for Venus, the Earth and Mars

    NASA Technical Reports Server (NTRS)

    Martin, A. M.; Righter, K.; Treiman, A. H.

    2010-01-01

    "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 calcite 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. Calcite 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+calcite. Very high contents of C and S are measured in some Earth s magmas, either dissolved or in the form of crystals (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) . Calcite is a major product of oceanic sedimentation and alteration of the crust. Therefore, sulfate- and calcite-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, calcite and anhydrite separately or on a combination of two. In this study we performed piston-cylinder experiments at 1 GPa between 950 and 1700 C using a mixture of 70wt% tholeiitic basalt + 15wt% anhydrite + 15wt% calcite. Up to 1440 C, an ultracalcic (CaO>13.5 wt%; CaO/Al2O3>1 wt%) picrobasaltic (SiO240-45 wt%; Na2O+K2O<2 wt%) melt containing up to 5 wt% SO3 and up to 5.3 wt% CO2+H2O (calculated by difference) is present in equilibrium with clinopyroxene, anhydrite, spinel-chromite, a CAS-phase and a gas composed mainly of CO and an aliphatic thiol (CH2)4SH. Hydrogen was incorporated either by contact between the starting material and air or by diffusion through the capsule during the experiments. The S content in the gas increases with temperature and run duration, implying that gases with various C/S ratios might be released during an impact or at subduction zones, depending on the P-T-t path and on the H content. Above approx.1440 C, a Ca-rich carbonate-sulfate melt forms (in equilibrium with the picrobasaltic melt) which contains a few percents of Na and K. Such melt is not expected to form at Earth s subduction temperatures. If it forms by meteorite impact, it might crystallize too fast to explain long flows like Venus canali. A different basalt/anhydrite/calcite ratio might, however, decrease its formation temperature.

  10. Dissolution enthalpies of synthetic magnesian calcites: Comparison with biogenic phases

    SciTech Connect

    Bischoff, W.D. . Geology Dept.); Wollast, R. )

    1992-01-01

    A series of synthetic magnesian calcites (0--15 mol% MgCO[sub 3]) were dissolved in weak acetic acid solutions to measure enthalpies of the reaction at 25 C. Heat released was 33.5 KJ/mol for calcite, decreasing to 33 KJ/mol for a Mg-Calcite of 2 mol% MgCO[sub 3], and increasing to 35 KJ/mol for a phase of 15 mol%. Excess enthalpies of formation Hf for these phases were calculated using calcite and magnesite as end-members. Values of Hf average about [minus]1 KJ/mol for the synthetic phases with a trend of increasingly negative values of Hf with Mg content. Excess entropies of formation Sf, corrected for excess entropies associated with ideal solid solutions, were calculated form available data on Gibbs free energies of formation and the values of Hf from this study. These values of Sf range from about [minus]2 J/mol-K for the phase with 2 mol% MgCO[sub 3] to [minus]5 J/mol-K at 15 mol%. The values of Sf suggest that some form of ordering (probably cation ordering) is obtained from these phases. In contrast, biogenic phases have positive values of Hf, increasing from about 1 KJ/mol for phases containing 5 mol% MgCO[sub 3] to 3 KJ/mol for those with 20 mol%. Values of Sf for the biogenic phases are positive, approximately 5 J/mol-K for a phase containing 15 mol% MgCO[sub 3]. For the biogenic phases, some form of disordering is suggested from the entropy calculations and may be the result of positional disordering is suggested from the entropy calculations and may be the result of positional disordering of the carbonate ion. The disorder in biogenic phases compared to the ordering in synthetic phases indicates significant structural differences that account for the higher solubilities of biogenic Mg-Calcites.

  11. Experimental study of the replacement of calcite by calcium sulphates

    NASA Astrophysics Data System (ADS)

    Ruiz-Agudo, E.; Putnis, C. V.; Hövelmann, J.; Álvarez-Lloret, P.; Ibáñez-Velasco, A.; Putnis, A.

    2015-05-01

    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 calcite (CaCO3) cleavage surfaces with sulphate-bearing acidic solutions, calcite 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 calcite by anhydrite. The reaction stops before equilibrium with respect to calcite 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 calcite attains equilibrium with respect to the bulk solution.

  12. Low-threshold collinear parametric Raman comb generation in calcite under 532 and 1064?nm picosecond laser pumping

    NASA Astrophysics Data System (ADS)

    Smetanin, S. N.; Jelínek, M., Jr.; Kube?ek, V.; Jelínková, H.

    2015-09-01

    Optimal conditions of low-threshold collinear parametric Raman comb generation in calcite (CaCO3) are experimentally investigated under 20 ps laser pulse excitation, in agreement with the theoretical study. The collinear parametric Raman generation of the highest number of Raman components in the short calcite crystals corresponding to the optimal condition of Stokes-anti-Stokes coupling was achieved. At the excitation wavelength of 1064?nm, using the optimum-length crystal resulted in the effective multi-octave frequency Raman comb generation containing up to five anti-Stokes and more than four Stokes components (from 674?nm to 1978?nm). The 532?nm pumping resulted in the frequency Raman comb generation from the 477?nm 2nd anti-Stokes up to the 692?nm 4th Stokes component. Using the crystal with a non-optimal length leads to the Stokes components generation only with higher thresholds because of the cascade-like stimulated Raman scattering with suppressed parametric coupling.

  13. Sr2+/Ca2+ and 44Ca/40Ca fractionation during inorganic calcite formation: III. Impact of salinity/ionic strength

    PubMed Central

    Tang, Jianwu; Niedermayr, Andrea; Köhler, Stephan J.; Böhm, Florian; K?sakürek, Basak; Eisenhauer, Anton; Dietzel, Martin

    2012-01-01

    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 crystallize inorganic calcite 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 calcite formation is mainly controlled by precipitation rate (R in ?mol/m2/h) and is weakly influenced by ionic strength/salinity. In analogy to Sr incorporation, 44Ca/40Ca fractionation during precipitation of calcite is weakly influenced by ionic strength/salinity too. At 25 °C the calcium isotope fractionation between calcite and aqueous calcium ions (?44/40Cacalcite-aq = ?44/40Cacalcite ? ?44/40Caaq) correlates inversely to log R values for all experiments. In addition, an inverse relationship between ?44/40Cacalcite-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 ?44/40Cacalcite-aq relationship, Sr/Ca and ?44/40Cacalcite values of precipitated calcite can be used as an excellent multi-proxy approach to reconstruct environmental conditions (e.g., temperature, precipitation rate) of calcite growth and diagenetic alteration. PMID:22347722

  14. Empirical calibration of the clumped isotope paleothermometer using calcites of1 various origins2

    E-print Network

    Schöne, Bernd R.

    Empirical calibration of the clumped isotope paleothermometer using calcites of1 various origins2 3 calibration of the clumped isotope thermometer for calcites of26 various mineralizing types calcites digested at 25 °C (Ghosh et al., 2006a)36 and from several other studies having confirmed

  15. Oxygen isotopes and MgCO3 in brachiopod calcite and a new paleotemperature equation

    E-print Network

    Zuschin, Martin

    Oxygen isotopes and MgCO3 in brachiopod calcite and a new paleotemperature equation Uwe Brand a Editor: David R. Hilton Keywords: Modern brachiopod calcite 18 O equilibrium Shell SrCO3 and MgCO3-squares regression analysis yields a new oxygen isotope paleotemperature equation for brachiopod calcite, which makes

  16. Magnesium isotope fractionation during precipitation of inorganic calcite under laboratory conditions

    E-print Network

    Johnson, Clark M.

    Magnesium isotope fractionation during precipitation of inorganic calcite under laboratory Available online 25 May 2012 Keywords: Mg isotope Mg-calcite carbonate isotope fractionation free fractionation factors between Mg-bearing calcite and aqueous Mg (Mg/Ca molar ratio between 3:1 and 13:1) from 20

  17. From structural to charge stability: Molecules on the insulating calcite (1014)

    E-print Network

    Ku?el, Petr

    1014-01-01

    From structural to charge stability: Molecules on the insulating calcite (1014) surface Seminá odd and to perform local manipulations. The calcite (1014) surface, a material itself highly relevant in biology molecules in an on-surface synthesis step [4]. Last, I will present results for a metallocene/calcite system

  18. Measurement of c-axis angular orientation in calcite (CaCO3) nanocrystals using

    E-print Network

    Coppersmith, Susan N.

    Measurement of c-axis angular orientation in calcite (CaCO3) nanocrystals using X-ray absorption are demonstrated here on geologic calcite (CaCO3) and used to investigate the prismatic layer of a mollusk shell, Pinctada fucata. These XANES-PEEM data reveal multiply oriented nanocrystals within calcite prisms

  19. Estimation of uncertain parameters to improve modeling of Mirobially Induced Calcite Precipitation

    E-print Network

    Cirpka, Olaf Arie

    Estimation of uncertain parameters to improve modeling of Mirobially Induced Calcite Precipitation in the subsurface or fracking could be reduced with sealing technologies like microbially induced calcite reactions rock grain calcite biofilm CO2 dissolved components suspended biomass water rockbiofilm brine w

  20. The solubility of fish-produced high magnesium calcite in seawater Ryan J. Woosley,1

    E-print Network

    Grosell, Martin

    The solubility of fish-produced high magnesium calcite in seawater Ryan J. Woosley,1 Frank J calcite as part of the physiological mechanisms responsible for maintaining salt and water balance 0.09) is approximately two times higher than aragonite and similar to the high magnesium calcite

  1. Peptide Controls on Calcite Mineralization: Polyaspartate Chain Length Affects Growth Kinetics and Acts as a Stereochemical

    E-print Network

    Dove, Patricia M.

    Peptide Controls on Calcite Mineralization: Polyaspartate Chain Length Affects Growth Kinetics interactions with step edges. Here, we show that the morphology and growth kinetics of calcite are modified suggest a process by which small fluctuations in primary structure in proteins can control calcite shape

  2. Empirical calibration of the clumped isotope paleothermometer using calcites of various origins

    E-print Network

    Schöne, Bernd R.

    Empirical calibration of the clumped isotope paleothermometer using calcites of various origins thermometer for calcites of various mineralizing types. These are an eggshell of an ostrich, a tropical from the first experimental calibration based on synthetic calcites digested at 25 °C (Ghosh et al

  3. Stabilization of Polar Step Edges on Calcite (10.4) by the Adsorption of Congo Red

    E-print Network

    Kühnle, Angelika

    Stabilization of Polar Step Edges on Calcite (10.4) by the Adsorption of Congo Red Rebecca Momper of calcite (10.4) by the presence of a water-soluble organic molecule, namely Congo Red. While characteristic. Especially calcite3,4 has attracted considerable attention in the context of additive

  4. Improvements in Modeling Microbially Induced Calcite Precipitation as a Leakage Mitigation Technology

    E-print Network

    Cirpka, Olaf Arie

    Improvements in Modeling Microbially Induced Calcite Precipitation as a Leakage Mitigation induced calcite precipitation (MICP). Other applications of MICP are discussed in [5]. Caprockfailure S + · x v - · Dpm, x = q reactions rock grain calcite biofilm CO2 dissolved components suspended biomass

  5. Fluids in the Crust Redox effects on calcite-portlandite-fluid equilibria at forearc conditions: Carbon

    E-print Network

    Manning, Craig

    Fluids in the Crust Redox effects on calcite-portlandite-fluid equilibria at forearc conditions: Carbon mobility, methanogenesis, and reduction melting of calcite Codi lazar*,1,2 , Chi zhang1,3 , Craig­10 kbar). Experimental calcite solubility was constant at O2 values from quartz-fayalite-magnetite (QFM

  6. SUPPORTING INFORMATION Surface-Potential Heterogeneity of Reacted Calcite and Rhodochrosite

    E-print Network

    S1 SUPPORTING INFORMATION Surface-Potential Heterogeneity of Reacted Calcite and Rhodochrosite histograms of steps and terraces for calcite and rhodochrosite surfaces of Figure 1. Figure S4: Topography for data shown in Figure 3 Sample Dependent Variable Probability (> F-Test Value)* h(nano) 2.6×10-4 calcite

  7. In situ AFM study of the dissolution and recrystallization behaviour of polished and stressed calcite surfaces

    E-print Network

    Dysthe, Dag Kristian

    calcite surfaces J. Bisschop a,*, D.K. Dysthe a , C.V. Putnis b , B. Jamtveit a a Physics of Geological in revised form 12 December 2005 Abstract We investigated the dissolution behaviour of polished calcite to study the effects of applied surface stress and crystallographic orientation on calcite dissolution

  8. On the complex conductivity signatures of calcite precipitation Susan Hubbard,1

    E-print Network

    Hubbard, Susan

    Click Here for Full Article On the complex conductivity signatures of calcite precipitation Yuxin; revised 24 November 2009; accepted 22 December 2009; published 5 May 2010. [1] Calcite is a mineral phase strengthening. Because induced calcite precipitation is typically quite variable in space and time, monitoring

  9. Molecular Self-Assembly of Enantiopure Heptahelicene-2-Carboxylic Acid on Calcite (1014)

    E-print Network

    Kühnle, Angelika

    1014-01-01

    Molecular Self-Assembly of Enantiopure Heptahelicene-2-Carboxylic Acid on Calcite (1014)-heptahelicene-2-carboxylic acid ((M)-[7]HCA) on the calcite (1014) cleavage plane under ultrahigh vacuum along the calcite [0110] direction. Here, we investigate the enantiopure (M)- [7]HCA compound, resulting

  10. A revised model for microbially induced calcite precipitation -improvements and insights

    E-print Network

    Cirpka, Olaf Arie

    A revised model for microbially induced calcite precipitation - improvements and insights Johannes technologies like microbially induced calcite precipitation (MICP). Other applications of MICP are discussed phases: t () = q reactions solutes: t x S + · x v - · Dpm, x = q reactions rock grain calcite

  11. Interactions of arsenic with calcite surfaces revealed by in situ nanoscale imaging

    E-print Network

    Montes-Hernandez, German

    Interactions of arsenic with calcite surfaces revealed by in situ nanoscale imaging Franc of contamination. In calcareous environments calcite may play an important role in arsenic solubility and transfer in water. Arsenic­calcite interactions remain controversial, especially for As(III) which was proposed

  12. Atomistic simulations of calcite nanoparticles and their interaction David J. Cooke and James A. Elliotta

    E-print Network

    Elliott, James

    Atomistic simulations of calcite nanoparticles and their interaction with water David J. Cooke 12 September 2007 Molecular dynamics MD simulations have been used to study the stability of calcite, an understand- ing of the chemical and physical properties of calcium car- bonate polymorphs, especially calcite

  13. Cite this: CrystEngComm, 2013, 15, Calcite formation by hydrothermal carbonation of

    E-print Network

    Montes-Hernandez, German

    Cite this: CrystEngComm, 2013, 15, 3392 Calcite formation by hydrothermal carbonation-Hernandezb and C. Noguera*cd The present study complements experimental results of calcite nanoparticle formation calcite particles ­ are considered. The simulation is performed with the help of the NANOKIN code

  14. From Viterbo Hot Springs More Aragonite Pearls (of wisdom), And Some Calcite Too Do Nannos Rule?

    E-print Network

    Catlos, Elizabeth

    From Viterbo Hot Springs ­ More Aragonite Pearls (of wisdom), And Some Calcite Too ­ Do Nannos Rule S-bacteria especially flourish, their slimy mucus slows the precipitation rate and calcite forms. The carbonate is mainly aragonite with some calcite (fig. 6); the aragonite forms as radial needles encrusting

  15. USE OF VATERITE AND CALCITE IN FORMING CALCIUM PHOSPHATE CEMENT A. Cuneyt Tas

    E-print Network

    Tas, A. Cuneyt

    USE OF VATERITE AND CALCITE IN FORMING CALCIUM PHOSPHATE CEMENT SCAFFOLDS A. Cuneyt Tas Department was that they all utilized single-phase CaCO3 (calcite or vaterite) in their powder components. The major phase with some varying amounts of unreacted CaCO3. Calcite powders used were needle-like or acicular in shape

  16. Crystallization and preliminary X-ray analysis of ginkbilobin-2 from Ginkgo biloba seeds: a novel antifungal protein with homology to the extracellular domain of plant cysteine-rich receptor-like kinases

    SciTech Connect

    Miyakawa, Takuya; Sawano, Yoriko; Miyazono, Ken-ichi; Hatano, Ken-ichi; Tanokura, Masaru

    2007-09-01

    Purification and crystallization 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 seeds 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 crystallized 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 crystals of both proteins belonged to the primitive cubic space group P2{sub 1}3, with unit-cell parameters a = b = c = 143.2 Å.

  17. SEED PRODUCTION

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This book chapter provides information at the upper division undergraduate and graduate student levels that describe the environmental factors and production practices that affect the capacity of forage crops to produce seeds. Consumers require dependable quantities of high quality seeds. Special ru...

  18. Fluid mediated transformation of aragonitic cuttlebone to calcite

    NASA Astrophysics Data System (ADS)

    Perdikouri, C.; Kasioptas, A.; Putnis, A.

    2009-04-01

    The aragonite to calcite transition has been studied extensively over the years because of its wide spectra of applications and of its significant geochemical interest. While studies of kinetics (e.g. Topor et al., 1981), thermodynamics (e.g. Wolf et al., 1996) and behavior of ions such as Sr and Mg (e.g. Yoshioka et al., 1986) have been made there are still unanswered questions regarding this reaction especially in the cases where the effects of fluid composition are considered. It is well known that when heated in air, aragonite transforms by a solid state reaction to calcite. The aragonite cuttlebone of the sepia officinalis that was used for our experiments undergoes a phase transition at ~370-390Ë? C, measured by in situ heating experiments in a Philips X'pert X-ray powder diffractometer equipped with a HTK 1200 High temperature oven. Successive X-ray scans were taken at isothermal temperatures at 200C intervals. A similar temperature range was found by Vongsavat et al. 2006, who studied this transition in Acropora corals. It is possible however to promote this transition at considerably lower temperatures by means of a fluid mediated reaction where the replacement takes place by a dissolution-precipitation mechanism (Putnis & Putnis, 2007). We have successfully carried out hydrothermal experiments where cuttlebone has been converted to calcite at 200Ë? C. Using the PhreeqC program we calculated the required composition of a solution that would be undersaturated with respect to aragonite and saturated with respect to calcite leading to dissolution of the aragonite and to a consequent precipitation of the new calcite phase, similar to the experiments described in an earlier study (Perdikouri et al, 2008). This reaction is not pseudomorphic and results in the destruction of the morphology, presumably due to the molar volume increase. A total transformation of the cuttlebone produced a fine calcite powder. The cuttlebone exhibits a unique microstructure, made up of interconnected chambers. The aragonite grown during biomineralization of the cuttlebone is interlaced with a β-chitin organic phase that provides the framework for the morphology that is observed. Experiments carried out with the same constant conditions but for different periods of time have revealed the evolution of the transformation to calcite. At shorter reaction times the product was made up of calcite powder and of well preserved aragonite septa, as was confirmed by powder X-ray diffraction. In other words, the vertical pillars appear to react at faster rates than the horizontal septa. It has been reported by Florek et al. 2008 that the septa contain higher quantities of β-chitin. The aim of this study is the investigation of these observations and the determination of the effect of the organic component on the kinetics of the aragonite to calcite transformation. Florek M., Fornal E., Gómez-Romero P., Zieba E., Paszkowicz W., Lekki J.,Nowak J., Kuczumow A. Materials Science and Engineering C, In Press (2008) Perdikouri C., Kasioptas A., Putnis C.V., Putnis A. Mineralogical Magazine 72, 111-114 (2008) Putnis A., Putnis C.V. Solid State Chemistry 180, 1783-1786 (2007) Topor N. D., Tolokonnikova L. I., Kadenatsi B. M. Journal of Thermal Analysis 20, 169-174 (1981) Vongsavat V., Winotai P., Meejoo S. Nuclear Instruments and Methods in Physics Research B 243, 167-173 (2006) Wolf G., Lerchner J., Schmidt H., Gamsjäger H., Königsberger E., Schmidt P. Journal of Thermal Analysis 46, 353-359 (1996) Yoshioka S., Ohde S., Kitano Y., Kanamori N. Marine Chemistry 18, 35-48 (1986)

  19. Patterns of biomediated CaCO3 crystal bushes in hot spring deposits

    NASA Astrophysics Data System (ADS)

    Peng, Xiaotong; Jones, Brian

    2013-08-01

    In the Eryuan hot spring, located in south China, the vent pool is covered with “crystal bushes”, up to 2 cm high, 1 cm in diameter, that grew in the biofilms that thrive in the spring waters that have a pH of 7.5 and a temperature of 88 °C. The biofilms are formed largely of phototrophic purple bacteria and green bacteria. Growth of the crystal bushes, which are formed of aragonite crystals (wheat-sheaves, radiating clusters), rhombohedral and dodecahedral calcite crystals, amorphous CaCO3 (ACC), and opal-A, is attributed to precipitation in the micro-domains of the biofilms where physiochemical conditions can vary on the sub-micron scale. There is no evidence that the calcite was formed through recrystallization of the metastable aragonite and most of the calcite crystals developed as mesocrystals that are characterized by incomplete growth and porous crystal faces. With the onset of diagenesis, there is a high probability that the crystal bushes will lose much of their identity as the (1) biofilm is lost through decay, (2) ACC and aragonite change to calcite, (3) identities of the mesocrystals and incompletely formed crystals are lost through continued precipitation and/or recrystallization, and (4) porous crystal faces are converted to solid crystal faces. This means that most of the features considered indicative of biomediated calcite precipitation have a low preservation potential and that the recognition of biomediated precipitates in old spring deposits may remain problematical.

  20. Microbially-Mediated Subsurface Calcite Precipitation for Removal of Hazardous Divalent Cations

    SciTech Connect

    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.

    2003-03-27

    We are investigating microbially-mediated acceleration of calcite precipitation and co-precipitation of hazardous divalent cations (e.g., 90Sr) in calcite 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 calcite precipitation. Lab studies indicated the ability of various bacteria to precipitate calcite through urea hydrolysis and that incorporation of strontium in biogenically-formed calcite is greater than in abiotically formed calcite. 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 calcite 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.

  1. U(VI) behaviour in hyperalkaline calcite systems

    NASA Astrophysics Data System (ADS)

    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

    2015-01-01

    The behaviour of U(VI) in hyperalkaline fluid/calcite systems was studied over a range of U(VI) concentrations (5.27 × 10-5 ?M to 42.0 ?M) 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 ?M 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 ?M) in the young cement leachate, U(VI) showed no interaction with the calcite surface over an 18 month period. Small angle X-ray scattering techniques indicated that at high U concentrations (42.0 ?M) and after 18 months, the U(VI) was present in a colloidal form which had little interaction with the calcite 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 calcite: in the system with 0.21 ?M U(VI), a liebigite-like Ca2UO2(CO3)3 surface complex was identified; at higher U(VI) concentrations (0.42 ?M), a second binding site of undetermined coordination was identified. At elevated U(VI) concentrations (>2.10 ?M) 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-calcite interface. Transmission electron microscope images of the section revealed that the calcite surface was coated with a nano crystalline, U containing phase. Selected area electron diffraction images of the U precipitate which was formed at a U(VI) concentration of 4.20 ?M were consistent with the formation of calcium uranate. XAS spectroscopy at higher concentrations (?21.0 ?M) suggested the formation of a second U(VI) phase, possibly a uranyl oxyhydroxide phase. These results indicated that in the young cement leachate, U(VI) did not react with the calcite surface unless U(VI) concentrations were very low (5.27 × 10-5 ?M). At higher concentrations, speciation calculations suggested that U(VI) was significantly oversaturated and experimental observations confirmed it existed in a colloidal form that interacted with the mineral surface only weakly. In the old cement leachate systems at low concentrations batch sorption and luminescence data suggested that U(VI) removal was being driven by a surface complexation mechanism. However, at higher concentrations, spectroscopic methods suggest a combination of both surface complexation and surface mediated precipitation was responsible for the observed removal. Overall, U(VI) behaviour in hyperalkaline calcite systems is distinct from that at circumneutral pH conditions: at high pH and anything but low U(VI) concentrations, a surface mediated precipitation mechanism occurs; this is in contrast to circumneutral pH conditions where U(VI) surface complexation reactions tend to dominate.

  2. Origin of gem corundum in calcite marble: The Revelstoke occurrence in the Canadian Cordillera of British Columbia

    NASA Astrophysics Data System (ADS)

    Dzikowski, Tashia J.; Cempírek, Jan; Groat, Lee A.; Dipple, Gregory M.; Giuliani, Gaston

    2014-06-01

    The calcite 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 crystals have elevated Cr2O3 (? 0.21 wt.%) and variable amounts of TiO2; rare blue rims on the corundum crystals 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 calcite (dolomite is very rare), the corundum was preserved because it did not react with dolomite to spinel + calcite during decompression. The scapolite-bearing assemblages formed during or after decompression of the rock at ~ 650 °C and 4-6 kbar. Gem-quality corundum crystals formed especially on borders of the mica-feldspar layers in an assemblage with calcite. 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 ?18O and ?13C 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 component of their protolith.

  3. Temperature Dependence of the Structural Parameters in the Transformation of Aragonite to Calcite, as Determined from In Situ Synchrotron Powder X-ray-Diffratction Data

    SciTech Connect

    Antao, Sytle M.; Hassan, Ishmael

    2011-09-06

    The temperature dependency of the crystal structure and the polymorphic transition of CaCO{sub 3} from aragonite to calcite 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 calcite, 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 calcite, 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 calcite, the CO{sub 3} groups change by a 30{sup o} rotation across the transition.

  4. Interaction of copper with the surface of calcite

    SciTech Connect

    Franklin, M.L.; Morse, J.W.

    1981-05-01

    The interaction of Cu ions in solution with the surface of calcite has been studied in a range of solutions from pure water to seawater. Observations of the uptake of Cu from solution onto calcite 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 calcite. A possible explanation for this behavior is the formation of a precipitate of malachite on the calcite surface. The value of K/sub s/ decreased slightly with increasing solid to solution ratios in seawater.

  5. Use of coupled passivants and consolidants on calcite mineral surfaces

    SciTech Connect

    Nagy, K.L.; Cygan, R.T.; Brinker, C.J.; Ashley, C.S.; Scotto, C.S.

    1997-02-01

    Deterioration of monuments, buildings, and works of art constructed of carbonate-based stone potentially can be arrested by applying a combination of chemical passivants and consolidants that prevent hydrolytic attack and mechanical weakening. The authors used molecular modeling and laboratory synthesis to develop an improved passivating agent for the calcite mineral surface based on binding strength and molecular packing density. The effectiveness of the passivating agent with and without a linked outer layer of consolidant against chemical weathering was determined through leaching tests conducted with a pH-stat apparatus at pH 5 and 25 C. For the range of molecules considered, modeling results indicate that the strongest-binding passivant is the trimethoxy dianionic form of silylalkylaminocarboxylate (SAAC). The same form of silylalkylphosphonate (SAP) is the second strongest binder and the trisilanol neutral form of aminoethylaminopropylsilane (AEAPS) is ranked third. Short-term leaching tests on calcite powders coated with the trisilanol derivative of SAAC, the triethoxy neutral form of SAP, and the trimethoxy neutral form of AEAPS show that the passivant alone does not significantly slow the dissolution rate. However, all passivants when linked to the sol consolidant result in decreased rates. Combined AEAPS plus consolidant results in a coating that performs better than the commercial product Conservare{reg_sign} OH and at least as well as Conservare{reg_sign} H. The modeling results indicate that there may be a threshold binding energy for the passivant above which the dissolution rate of calcite is actually enhanced. More strongly-binding passivants may aid in the dissolution mechanism or dissociate in aqueous solution exposing the calcite surface to water.

  6. String stabilized ribbon growth a method for seeding same

    DOEpatents

    Sachs, Emanuel M. (39 Harding Ave., Belmont, MA 02178)

    1987-08-25

    This invention is a method of initiating or seeding the growth of a crystalline or polycrystalline ribbon by the String Stabilized Ribbon Growth Method. The method for seeding the crystal growth comprises contacting a melt surface with a seed and two strings used in edge stabilization. The wetted strings attach to the wetted seed as a result of the freezing of the liquid melt. Upon drawing the seed, which is attached to the strings, away from the melt surface a melt liquid meniscus, a seed junction, and a growth interface forms. Further pulling of the attached seed causes a crystal ribbon to grow at the growth interface. The boundaries of the growing ribbon are: at the top the seed junction, at the bottom the freezing boundary of the melt liquid meniscus, and at the edges frozen-in strings.

  7. Arsenite sorption and co-precipitation with calcite

    E-print Network

    Roman-Ross, Gabriela; Turrillas, Xavier; Fernandez-Martinez, Alejandro; Charlet, Laurent

    2008-01-01

    Sorption of As(III) by calcite was investigated as a function of As(III) concentration, time and pH. The sorption isotherm, i.e. the log As(III) vs. log [As(OH)3 degrees / Assat] plot is S-shaped and has been modelled on an extended version of the surface precipitation model. At low concentrations, As(OH)3 degrees is adsorbed by complexation to surface Ca surface sites, as previously described by the X-ray standing wave technique. The inflexion point of the isotherm, where As(OH)3 degrees is limited by the amount of surface sites (ST), yields 6 sites nm-2 in good agreement with crystallographic data. Beyond this value, the amount of sorbed arsenic increases linearly with solution concentration, up to the saturation of arsenic with respect to the precipitation of CaHAsO3(s). The solid solutions formed in this concentration range were examined by X-ray and neutron diffraction. The doped calcite lattice parameters increase with arsenic content while c/a ratio remains constant. Our results made on bulk calcite on...

  8. Earthworm-produced calcite granules: A new terrestrial palaeothermometer?

    NASA Astrophysics Data System (ADS)

    Versteegh, Emma A. A.; Black, Stuart; Canti, Matthew G.; Hodson, Mark E.

    2013-12-01

    In this paper we show for the first time that calcite granules, produced by the earthworm Lumbricus terrestris, and commonly recorded at sites of archaeological interest, accurately reflect temperature and soil water ?18O 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 calcite granules were collected from the second set of soils. ?18O values were determined on individual calcite granules (?18Oc) and the soil solution (?18Ow). The ?18Oc values reflect soil solution ?18Ow 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 ? = [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.

  9. Seeding Rangeland. 

    E-print Network

    Welch, Tommy G.; Rector, Barron S.; Alderson, James S.

    1993-01-01

    ? This publication was funded by the State Agricultural Soil and Water Conservation Fund. ' Seeding Rangeland Tommy G. Welch, Barron S. Rector and James S. Alderson* Soil and water conservation, high quality forage production for livestock and wildlife... met by alter ing vegetation composition through rangeland seeding include soil stabilization, improved water infiltration, improved vegetation ground cover for reduced water runoff, return to a prairie-like vegeta tion and improved wildlife...

  10. Carbonate "clumped" isotope signatures in aragonitic scleractinian and calcitic gorgonian deep-sea corals

    DOE PAGESBeta

    Kimball, J.; Tripati, R. E.; Dunbar, R.

    2015-12-04

    Deep-sea corals are a potentially valuable archive of the temperature and ocean chemistry of intermediate and deep waters. Living in near constant temperature, salinity and pH, and having amongst the slowest calcification rates observed in carbonate-precipitating biological organisms, deep-sea corals can provide valuable constraints on processes driving mineral equilibrium and disequilibrium isotope signatures. Here we report new data to further develop "clumped" isotopes as a paleothermometer in deep-sea corals as well as to investigate mineral-specific, taxon-specific, and growth-rate related effects. Carbonate clumped isotope thermometry is based on measurements of the abundance of the doubly-substituted isotopologue 13C18O16O2 in carbonate minerals, analyzedmore »in CO2 gas liberated on phosphoric acid digestion of carbonates and reported as ?47 values. We analyzed ?47 in live-collected aragonitic scleractinian (Enallopsammia sp.) and calcitic gorgonian (Isididae and Coralliidae) deep-sea corals, and compared results to published data for other aragonitic scleractinian taxa. Measured ?47 values were compared to in situ temperatures and the relationship between ?47 and temperature was determined for each group to investigate taxon-specific effects. We find that aragonitic scleractinian deep-sea corals exhibit higher values than calcitic gorgonian corals and the two groups of coral produce statistically different relationship between ?47-temperature calibrations. These data are significant in the interpretation of all carbonate "clumped" isotope calibration data as they show that distinct ?47-temperature calibrations can be observed in different materials recovered from the same environment and analyzed using the same instrumentation, phosphoric acid composition, digestion temperature and technique, CO2 gas purification apparatus, and data handling. There are three possible explanations for the origin of these different calibrations. The offset between the corals of different mineralogy is in the same direction as published theoretical predictions for the offset between calcite and aragonite, although the magnitude of the offset is different. One possibility is that the deep-sea coral results reflect that crystals 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 crystals. 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, calcite, and aragonite may have similar clumped isotope acid digestion fractionation factors, the influence of acid digestion kinetics on ?47 is a subject that warrants further investigation.« less

  11. Interaction of copper with the surface of calcite

    SciTech Connect

    Franklin, M.L.; Morse, J.W.

    1981-12-01

    The interaction of Cu ions in solution with the surface of calcite has been studied in a range of solutions from pure water to seawater. Observations of the uptake of Cu from solution onto calcite 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 calcite 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 calcite. A possible explanation for this behavior is the formation of a precipitate of malachite on the calcite surface. The value of K/sub s/ decreased slightly with increasing solid to solution ratios in seawater.

  12. Strontium isotope fractionation of planktic foraminifera and inorganic calcite

    NASA Astrophysics Data System (ADS)

    Böhm, Florian; Eisenhauer, Anton; Tang, Jianwu; Dietzel, Martin; Krabbenhöft, Andre; Kisakürek, Basak; Horn, Christian

    2012-09-01

    We have investigated the strontium isotope fractionation (?88/86Srcarb-aq) between inorganic calcite and aqueous Sr2+ ions by precipitation experiments at a constant temperature of 25 °C and precipitation rates (R) ranging from 102.3 to 104.2 ?mol/m2/h. Strontium isotope ratios were measured using the 87Sr-84Sr double spike technique. It was found that strontium isotope fractionation in these calcites is strongly dependent on the precipitation rate: ?Sr carb-aq =-0.08?log(R[?mol/m/h])+0.08 The measured ?88/86Sr values are significantly correlated with previously measured ?44/40Ca and Sr/Ca values of the same calcite samples: ?Sr=+0.18??Ca-0.01 ?Sr=-1.5?KdSr-0.03 The slope of 88Sr/86Sr versus 44Ca/40Ca fractionation is 0.18 ± 0.04 and compatible with a kinetic fractionation during dehydration of the strontium and calcium ions, but not with isotope fractionation in a diffusive boundary layer. Using published equilibrium ?44/40Cacarb-aq and KdSr values we estimate the equilibrium isotope fractionation of strontium to be very close to zero (?88/86Sreq(carb-aq) = -0.01 ± 0.06‰). This estimate is confirmed by strontium isotope values of natural inorganic calcites that precipitated very slowly in basalts of the ocean crust. The results from the inorganic calcites are used to explain strontium isotope fractionation of planktic foraminifera. Specimens of two warm water species (Globigerinoides ruber and Globigerinoides sacculifer) were picked from the Holocene section of a Caribbean sediment core. We found no significant difference in ?88/86Sr between the two species. In addition, G. ruber specimens from Marine Isotope Stage 2 in the same core show ?88/86Sr values identical to the Holocene specimens. The strontium isotopes of both foraminifera species are strongly fractionated (?88/86Srcarb-aq = -0.248 ± 0.005‰) when compared to published data of other major marine calcifiers. Applying the results from the inorganic precipitation experiments we find that the strong foraminiferal strontium isotope fractionation can be explained by calcification in a largely open system at high precipitation rates, comparable in magnitude to rates known from scleractinian reef corals. This interpretation is in good agreement with the kinetic calcification model for planktic foraminifera by Kisakürek et al. (2011), which was based on calcium isotopes and elemental Sr/Ca ratios.

  13. Aqueous synthesis and transmission electron microscopy observation of seed-grown spherical ferrite nanoparticles

    NASA Astrophysics Data System (ADS)

    Tanaka, T.; Tada, M.; Nakagawa, T.; Abe, M.

    2012-03-01

    Uniform-sized spherical iron ferrite nanoparticles grew on seed crystals in an aqueous solution containing sucrose. Using the seed crystals which were highly dispersed in acidic or alkaline seed-crystal suspension without relation to pH of the suspension, we widely controlled the particle diameter in the range 20-200 nm by changing the additive amount of the seed crystals. By transmission electron microscopy observation and X-ray diffraction analysis, it indicated that the particles were highly crystalline but not amorphous. Selected area diffraction patterns of the particles by using transmission electron microscope revealed that the particles were composed of one to several crystals. Thus we provided the evidence that the particles grew on clusters composed of one to several seed crystals to which those of several dozen seed crystals were disintegrated.

  14. Titania single crystals with a curved surface.

    PubMed

    Yang, Shuang; Yang, Bing Xing; Wu, Long; Li, Yu Hang; Liu, Porun; Zhao, Huijun; Yu, Yan Yan; Gong, Xue Qing; Yang, Hua Gui

    2014-01-01

    Owing to its scientific and technological importance, crystallization as a ubiquitous phenomenon has been widely studied over centuries. Well-developed single crystals are generally enclosed by regular flat facets spontaneously to form polyhedral morphologies because of the well-known self-confinement principle for crystal growth. However, in nature, complex single crystalline calcitic skeleton of biological organisms generally has a curved external surface formed by specific interactions between organic moieties and biocompatible minerals. Here we show a new class of crystal surface of TiO?, which is enclosed by quasi continuous high-index microfacets and thus has a unique truncated biconic morphology. Such single crystals may open a new direction for crystal growth study since, in principle, crystal growth rates of all facets between two normal {101} and {011} crystal surfaces are almost identical. In other words, the facet with continuous Miller index can exist because of the continuous curvature on the crystal surface. PMID:25373513

  15. Microstructural and compositional study of a bulk Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}-PbTiO{sub 3} single crystal grown from a BaTiO{sub 3} seed

    SciTech Connect

    Samardzija, Zoran . E-mail: zoran.samardzija@ijs.si; Jeon, Jae-Ho; Ceh, Miran

    2007-06-15

    The microstructure, composition and homogeneity of a Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}-PbTiO{sub 3} (PMNT) single crystal were studied using a combination of electron-microprobe techniques: scanning electron microscopy, orientation analysis and quantitative X-ray microanalysis. A PMNT single crystal was grown from a polycrystalline PMNT matrix using a BaTiO{sub 3} single crystal as a seed. The PMNT crystal retained the same crystallographic orientation as the seed with no interdiffusion at the interface. The average chemical composition, determined with optimized quantitative wavelength-dispersive X-ray microanalysis, was Pb(Mg{sub 1/3}Nb{sub 2/3}){sub 1-X}Ti {sub X}O{sub 3} where x = 0.33. A statistical evaluation of the data using the analysis of variance showed that the achieved experimental uncertainty was below {+-} 1% relative. The compositional homogeneity of the crystal was verified on the micrometer-scale; however on the macro-scale slight fluctuations of the Mg, Nb and Ti concentrations were observed across the crystal. The measured variations from the average composition were {+-} 2.3% relative for Ti, {+-} 1.3% for Nb and {+-} 1.4% for Mg. In contrast, the Pb concentration was found to be uniform on both the micro- and macro-scale, showing a variation below {+-} 0.5% relative.

  16. Aragonite–calcite–vaterite: A temperature influenced sequential polymorphic transformation of CaCO{sub 3} in the presence of DTPA

    SciTech Connect

    Gopi, Shanmukhaprasad; Subramanian, V.K.; Palanisamy, K.

    2013-05-15

    Highlights: ? Crystallization of CaCO{sub 3} between 60 and 230 °C in the presence of DTPA. ? Formation of exclusive and individual polymorphs at different temperatures. ? Violation of second law of thermodynamics/Ostwald rule of stages has been observed. - Abstract: Calcium carbonate was precipitated from calcium chloride using sodium carbonate in the presence of diethylenetriaminepentaacetic acid (DTPA) between 60 and 230 °C. The samples were characterized by FTIR, Raman, XRD and SEM techniques. CaCO{sub 3} with different crystal morphologies such as spherolite/datura pod, dumbbell, peanut, were obtained depending on the experimental conditions. The results showed that pure aragonite, calcite and vaterite were formed at low, moderate and high temperatures respectively. A binary mixture of calcite and vaterite was resulted between 150 and 200 °C. The data suggested an unusual conversion of stable calcite to meta stable vaterite at higher temperature in presence of DTPA. The study revealed a novel methodology for the exclusive/individual preparation of different crystalline polymorphs of CaCO{sub 3}. Formation of pure vaterite above 200 °C divulged the possibility of DTPA as a potential scale inhibitor and boiler sludge conditioner at elevated temperatures.

  17. Circular economy in drinking water treatment: reuse of ground pellets as seeding material in the pellet softening process.

    PubMed

    Schetters, M J A; van der Hoek, J P; Kramer, O J I; Kors, L J; Palmen, L J; Hofs, B; Koppers, H

    2015-01-01

    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 calcite 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 seeding material in pellet softening were tested with two pilot reactors in parallel. In one reactor, garnet sand was used as seeding material, in the other ground calcite. Garnet sand and ground calcite performed equally well. An economic comparison and a life-cycle assessment were made as well. The results show that the reuse of ground calcite as seeding 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 calcite will be made at full scale, based on this pilot plant research. PMID:25746637

  18. Module: Material Structure Focus: Hydrogen Bonding & Crystallization.

    E-print Network

    Rowley, Clarence W.

    and demonstrate the process of growing crystals. Materials: Water Copper Sulfate Cup Petri Dish Petri Dish Water sulfate in each Petri dish to act as a "seed" crystal. I came across another crystal growing exerciseModule: Material Structure Focus: Hydrogen Bonding & Crystallization. Duration: 43 minute period

  19. The sensitized luminescence of manganese-activated calcite

    USGS Publications Warehouse

    Schulman, J.H.; Evans, L.W.; Ginther, R.J.; Murata, K.J.

    1947-01-01

    Synthetic manganese-activated calcites 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 calcites 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 calcites 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.".

  20. Dynamic recrystallization processes of calcitic fossils in deformed marble

    NASA Astrophysics Data System (ADS)

    Lee, S.; Ree, J. H.; Jung, H.

    2014-12-01

    Here we report dynamic recrystallization processes of calcitic fossils in weakly to fully recrystallized marbles to discuss the survivability of fossils and possible recognition of former fossils in fully recrystallized marbles. The marble is from the early Paleozoic sequence in the Jeongseon area of South Korea. Each crinoid stem in a weakly or non-recrystallized marble cut perpendicular to its length appears as a donut shape and consists of five calcite grains (300-500µm in size) with the same c-axis but different a-axis orientations. The misorientation angle between adjacent grains in a crinoid stem is 40-50°. The outer and inner diameters of the donut-shaped crinoid stems are about 900 and 500 µm, respectively. The recrystallization processes initiate on grain boundaries as bulging recrystallization while transgranular subgrain walls form within lattice-distorted grains. New grains also nucleate on twin boundaries and subgrain boundaries. Some subgrain walls become grain boundaries as they collect more dislocations with subgrain boundary migration. The newly recrystallized grains grow to reach a steady-state grain size of 20-50µm. In fully recrystallized and deformed marbles, the crinoid stems occur as elongated donut-shaped calcite aggregates. The crinoid stems can be recognized by their size larger than that of recrystallized matrix grains (5-20µm), With a higher degree of dynamic recrystallization, the randomness of the misorientation angle distribution of the recrystallized grains within a crinoid stem increases, indicating weaker lattice preferred orientation. We are trying to test whether lattice orientation maps (or AVA diagrams) can be used to recognize former fossil traces in fully recrystallized marbles.

  1. Top-seed solution growth and characterization of AlSb single crystals for gamma-ray detectors. Final report, 1 October 1994--30 September 1995

    SciTech Connect

    Witt, A.F.; Becla, P.; Counterman, C.; DiFrancesco, J.; Landahl, G.; Morse, K.; Sanchez, J.

    1996-01-26

    The ultimate objective of the conducted research is to ascertain the potential of AlSb (in single crystal form) for application as {gamma}-detector material operating at room temperature. To this end approaches to crystal 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 crystals 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 crystal 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.

  2. Synthesis of KCa2Nb3O10 Crystals with Varying Grain Sizes and Their Nanosheet Monolayer Films As Seed Layers for PiezoMEMS Applications.

    PubMed

    Yuan, Huiyu; Nguyen, Minh; Hammer, Tom; Koster, Gertjan; Rijnders, Guus; Ten Elshof, Johan E

    2015-12-16

    The layered perovskite-type niobate KCa2Nb3O10 and its derivatives show advantages in several fields, such as templated film growth and (photo)catalysis. Conventional synthesis routes generally yield crystal size smaller than 2 ?m. We report a flux synthesis method to obtain KCa2Nb3O10 crystals with significantly larger sizes. By using different flux materials (K2SO4 and K2MoO4), crystals with average sizes of 8 and 20 ?m, respectively, were obtained. The KCa2Nb3O10 crystals from K2SO4 and K2MoO4 assisted synthesis were protonated and exfoliated into monolayer nanosheets, and the optimal exfoliation conditions were determined. Using pulsed laser deposition, highly (001)-oriented piezoelectric stacks (SrRuO3/PbZr0.52Ti0.48O3/SrRuO3, SRO/PZT/SRO) were deposited onto Langmuir-Blodgett films of Ca2Nb3O10(-) (CNO) nanosheets with varying lateral nanosheet sizes on Si substrates. The resulting PZT thin films showed high crystallinity irrespective of nanosheet size. The small sized nanosheets yielded a high longitudinal piezoelectric coefficient d33 of 100 pm/V, while the larger sized sheets had a d33 of 72 pm/V. An enhanced transverse piezoelectric coefficient d31 of -107 pm/V, an important input parameter for the actuation of active structures in microelectromechanical systems (MEMS) devices, was obtained for PZT films grown on CNO nanosheets with large lateral size, while the corresponding value on small sized sheets was -96 pm/V. PMID:26583282

  3. The ubiquitous nature of accessory calcite in granitoid rocks: Implications for weathering, solute evolution, and petrogenesis

    USGS Publications Warehouse

    White, A.F.; Schulz, M.S.; Lowenstern, J. B.; Vivit, D.V.; Bullen, T.D.

    2005-01-01

    Calcite 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 calcite in granitoid rocks. This study addresses this issue by analyzing a worldwide distribution of more than 100 granitoid rocks. Calcite 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). Calcite occurrences include small to large isolated anhedral grains, fracture and cavity infillings, and sericitized cores of plagioclase. No correlation exists between the amount of calcite present and major rock oxide compositions, including CaO. Ion microprobe analyses of in situ calcite 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 calcite relative to silicate minerals. The correlation of these parameters with higher calcite concentrations decreases as leachates approach thermodynamic saturation. In longer term column experiments (1.5 yr), reactive calcite becomes exhausted, solute Ca and Sr become controlled by feldspar dissolution and 87Sr/ 86Sr by biotite oxidation. Some accessory calcite in granitoid rocks is related to intrusion into carbonate wall rock or produced by later hydrothermal alteration. However, the ubiquitous occurrence of calcite 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, calcite is a stable phase at temperatures of 400 to 700??C. Copyright ?? 2005 Elsevier Ltd.

  4. Utilization of calcite and waste glass for preparing construction materials with a low environmental load.

    PubMed

    Maeda, Hirotaka; Imaizumi, Haruki; Ishida, Emile Hideki

    2011-11-01

    In this study, porous calcite materials are hydrothermally treated at 200 °C using powder compacts consisting of calcite 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 calcite and glass in the hydrothermal treatment plays an important role in the solidification of calcite without thermal decomposition. PMID:21794973

  5. Project SEED.

    ERIC Educational Resources Information Center

    Chemical and Engineering News, 1986

    1986-01-01

    Reports on Project SEED (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.…

  6. A generalised chemical precipitation modelling approach in wastewater treatment applied to calcite.

    PubMed

    Mbamba, Christian Kazadi; Batstone, Damien J; Flores-Alsina, Xavier; Tait, Stephan

    2015-01-01

    Process simulation models used across the wastewater industry have inherent limitations due to over-simplistic descriptions of important physico–chemical reactions, especially for mineral solids precipitation. As part of the efforts towards a larger Generalized Physicochemical Modelling Framework, the present study aims to identify a broadly applicable precipitation modelling approach. The study uses two experimental platforms applied to calcite precipitating from synthetic aqueous solutions to identify and validate the model approach. Firstly, dynamic pH titration tests are performed to define the baseline model approach. Constant Composition Method (CCM) experiments are then used to examine influence of environmental factors on the baseline approach. Results show that the baseline model should include precipitation kinetics (not be quasi-equilibrium), should include a 1st order effect of the mineral particulate state (Xcryst) and, for calcite, have a 2nd order dependency (exponent n = 2.05 ± 0.29) on thermodynamic supersaturation (?). Parameter analysis indicated that the model was more tolerant to a fast kinetic coefficient (kcryst) and so, in general, it is recommended that a large kcryst value be nominally selected where insufficient process data is available. Zero seed (self nucleating) conditions were effectively represented by including arbitrarily small amounts of mineral phase in the initial conditions. Both of these aspects are important for wastewater modelling, where knowledge of kinetic coefficients is usually not available, and it is typically uncertain which precipitates are actually present. The CCM experiments confirmed the baseline model, particularly the dependency on supersaturation. Temperature was also identified as an influential factor that should be corrected for via an Arrhenius-style correction of kcryst. The influence of magnesium (a common and representative added impurity) on kcryst was found to be significant but was considered an optional correction because of a lesser influence as compared to that of temperature. Other variables such as ionic strength and pH were adequately captured by the quasi-equilibrium description of the aqueous-phase and no further kinetic corrections were required. The baseline model is readily expandable to include other precipitation reactions. For simple representations, large values for kcryst with n = 2 (or n = 2 or 3 for other minerals, as appropriate) should be selected without corrections to kcryst. Where accuracy is required (e.g., in mechanistic studies), machine estimation of kcryst should be performed with robust process data and kcryst should at least be corrected for temperature. PMID:25462741

  7. Environmental controls on the Emiliania huxleyi calcite mass

    NASA Astrophysics Data System (ADS)

    Horigome, M. T.; Ziveri, P.; Grelaud, M.; Baumann, K.-H.; Marino, G.; Mortyn, P. G.

    2013-06-01

    Although ocean acidification is expected to impact (bio)calcification by decreasing the seawater carbonate ion concentration, [CO32-], there exists evidence of non-uniform response of marine calcifying plankton to low seawater [CO32-]. This raises questions on the role of environmental factors other than acidification and on the complex physiological responses behind calcification. Here we investigate the synergistic effect of multiple environmental parameters, including temperature, nutrient (nitrate and phosphate) availability, and seawater carbonate chemistry on the coccolith calcite 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 well above the modern lysocline. The coccolith calcite mass in our results presents a latitudinal distribution pattern that mimics the main oceanographic features, thereby pointing to the potential importance of phosphorus and temperature in determining coccolith mass by affecting primary calcification and possibly driving the E. huxleyi morphotype distribution. This evidence does not necessarily argue against the potentially important role of the rapidly changing seawater carbonate chemistry in the future, when unabated fossil fuel burning will likely perturb ocean chemistry beyond a critical point. Rather 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.

  8. Environmental controls on the Emiliania huxleyi calcite mass

    NASA Astrophysics Data System (ADS)

    Horigome, M. T.; Ziveri, P.; Grelaud, M.; Baumann, K.-H.; Marino, G.; Mortyn, P. G.

    2014-04-01

    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 calcite 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 calcite 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.

  9. Kinetic Strontium Isotope Fractionation of Planktic Foraminifera and Inorganic Calcite

    NASA Astrophysics Data System (ADS)

    Boehm, F.; Eisenhauer, A.; Horn, C.; Kisakurek, B.; Krabbenhoeft, A.; Tang, J.; Niedermayr, A.; Dietzel, M.

    2010-12-01

    We have studied the strontium isotope fractionation of the planktic foraminifera species Globigerinoides ruber and G. sacculifer from a Caribbean core comprising the last 25 kyr. Isotope ratios were measured using a 87Sr-84Sr double spike and are reported as ?88/86Sr relative to NIST SRM987 (Krabbenhöft et al. 2009, JAAS 24, 1267-1271). We found that strontium isotopes in the two foraminifera species are more strongly fractionated than in most other major marine calcifiers reported by Krabbenhöft et al. (2010, GCA 74, 4097-4109). No significant difference in the Sr isotopic composition between the two species was detected for either Holocene or glacial samples. Water temperatures based on Mg/Ca ratios show downcore variations of about 3°C. G. sacculifer displays a weak negative temperature relationship of about -0.005 permill/°C in ?88/86Sr (R2=0.59, p=0.013). No significant temperature dependence was found for G. ruber. In order to explain the strong Sr isotope fractionation of the foraminifera we investigated inorganic calcite that was precipitated in laboratory experiments with a range of precipitation rates (log(R) of 2.3 to 4.2 µmol/m2/h), at a constant temperature of 25°C. The inorganic calcite was previously used in a Ca isotope study which detected a strong influence of precipitation rate on isotope fractionation (Tang et al. 2008, GCA 72, 3733-3745). We found that Sr isotope fractionation is also strongly dependent on the precipitation rate (?88/86Sr= -0.084*log(R)+0.08, R2=0.87, p=0.003, n=6). Strontium and Ca isotope ratios of the inorganic calcite samples are positively correlated. The slope of 88Sr/86Sr ratios versus 44Ca/40Ca ratios is +0.184 (R2=0.96). This value is compatible with a chemical kinetic fractionation of the respective hydrated cations (e.g. during dehydration). Extrapolating to very slow precipitation rates we estimate the equilibrium isotope fractionation (?44/40Ca and ?88/86Sr) for both elements to be very close to 0. This estimate is confirmed by isotope values of natural inorganic calcites that grew in ocean crust basalts with very slow precipitation rates (Böhm et al. 2009, GCA 73/13 Suppl. 1, A133). It further agrees with the Ca isotope equilibrium fractionation value for calcite of 0 permill determined by Fantle and DePaolo (2007, GCA 71, 2524-2546) and Jacobson and Holmden (2008, EPSL 270, 349-353). Inorganic aragonite, on the other hand, shows no indication of a rate dependence for Sr and Ca isotope fractionation. Applying the results from the inorganic experiments to the planktic foraminifera we find that the strong Sr isotope fractionation can be explained by the formation of the shells in a largely open system at very high precipitation rates, comparable in magnitude to rates known from scleractinian reef corals. This interpretation is in good agreement with the kinetic calcification model for planktic foraminifera by Kisakurek et al. (2008, Eos 89(53) Fall Meet. Suppl. B11C-0382), which was based on Ca isotopes and elemental Sr/Ca ratios.

  10. Stable carbon isotopes and lipid biomarkers provide new insight into the formation of calcite and siderite concretions in organic-matter rich deposits

    NASA Astrophysics Data System (ADS)

    Baumann, Lydia; Birgel, Daniel; Wagreich, Michael; Peckmann, Jörn

    2015-04-01

    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 calcite 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. Calcite concretions consist of abundant calcite microspar (80-90 vol.%), as well as detrital minerals and iron oxyhydroxides. The septarian cracks show beginning cementation with dog-tooth calcite to varying degrees. Framboidal pyrite occurs in some of the calcite concretions, pointing to bacterial sulfate reduction. Siderite concretions consist of even finer carbonate crystals, mainly siderite (40-70 vol.%) but also abundant ferroan calcite, accompanied by iron oxyhydroxides and detrital minerals. The ?13C values of the calcite concretions (-6.8 to -4.1o ) most likely reflect a combination of bacterial organic matter oxidation and input of marine biodetrital carbonate. The ?18O 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 ?13C and ?18O values. The siderite ?13C values (-11.1 to -7.5o ) point to microbial respiration of organic carbon and the ?18O values (-3.5 to +2.2o ) agree with a marine depositional environment. In contrast to the calcite concretions, the stable isotope composition of the host sediment differs significantly from the siderite concretions. The ?13C values of the Gosau host sediment reflect marine conditions, whereas the oxygen isotope values are best explained by meteoric overprint. Lipid biomarkers have been extracted before and after dissolution of the concretions in order to assess their authenticity and to exclude recent surface contamination. In the following, only the biomarkers extracted after dissolution are discussed, since they are thought to be related to concretion formation. The calcite concretions comprise abundant plant wax derived long-chain n-alkanes, reflecting high terrestrial input. Bacterial, terminally-branched fatty acids were found, but in overall low abundance. The siderite concretions did not yield biomarkers due to their high maturity. No archaeal biomarkers were found in any of the concretions. Considering the presence of framboidal pyrite, the moderately low ?13C values, and the biomarker inventory, bacterial sulfate reduction apparently contributed to the formation of the calcite concretions in a brackish environment. In contrast, ongoing sulfate reduction and resultant hydrogen sulfide production inhibit siderite precipitation. Therefore, the low ?13C values of the siderite concretions are best explained by bacterial iron reduction.

  11. Interactions of arsenic with calcite surfaces revealed by in-situ nanoscale imaging

    NASA Astrophysics Data System (ADS)

    Renard, Francois; Putnis, Christine; Montes-Hernandez, German; Ruiz-Agudo, Encarnacion; Hövelmann, Jörn; Sarret, Géraldine

    2015-04-01

    Arsenic dissolved in water represents a key environmental and health challenge because several million people are under the threat of contamination. In calcareous environments calcite may play an important role in arsenic solubility and transfer in water. Arsenic-calcite 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 calcite 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) calcite 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 calcite surface, and XAS results showed that As(V) was mostly incorporated in the calcite structure. For As(III), AFM results showed much less impact on calcite 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 calcite and the resulting calcite contained 36% As(III) and 64% As(V). All these experimental results confirm that As(V) has a much stronger interaction with calcite than As(III) and that calcite may represent an important reservoir for arsenic in various geological environments.

  12. BULK SEED TENDERS FOR HANDLING PEANUT SEED

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Planting is a very labor intensive operation requiring both skilled and unskilled labor. Intense manual labor is required to load seed hoppers on the planter. A seeding rate of 112 kg/ha, requires 11.2 t of seed per 100 ha planted. Bulk seed tenders have been used in the Midwestern United States to ...

  13. In situ study of the R{bar 3}c-R{bar 3}m orientational disorder in calcite.

    SciTech Connect

    Antao, S. M.; Hassan, I.; Mulder, W. H.; Lee, P. L.; Toby, B. H.; X-Ray Science Division; Univ. of West Indies

    2009-01-01

    The temperature dependences of the crystal structure and intensities of the (113) and (211) reflections in calcite, CaCO{sub 3}, were studied using Rietveld structure refinements based on synchrotron powder X-ray diffraction data. Calcite 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.

  14. Genesis of amethyst geodes in basaltic rocks of the Serra Geral Formation (Ametista do Sul, Rio Grande do Sul, Brazil): a fluid inclusion, REE, oxygen, carbon, and Sr isotope study on basalt, quartz, and calcite

    NASA Astrophysics Data System (ADS)

    Gilg, H. Albert; Morteani, Giulio; Kostitsyn, Yuri; Preinfalk, Christine; Gatter, Istvan; Strieder, Adelir J.

    2003-12-01

    In the Ametista do Sul area, Rio Grande do Sul, Brazil, amethyst-bearing geodes are hosted by a ~40- to 50-m-thick subhorizontal high-Ti basaltic lava flow of the Lower Cretaceous Paraná Continental Flood Basalt Province. The typically spherical cap-shaped, sometimes vertically elongated geodes display an outer rim of celadonite followed inwards by agate and colorless and finally amethystine quartz. Calcite formed throughout the whole crystallization sequence, but most commonly as very late euhedral crystals, sometimes with gypsum, in the central cavity. Fluid inclusions in colorless quartz and amethyst are predominantly monophase and contain an aqueous liquid. Two-phase liquid-vapor inclusions are rare. Some with a consistent degree of fill homogenize into the liquid between 95 and 98 °C. Ice-melting temperatures in the absence of a vapor phase between -4 and +4 °C indicate low salinities. Chondrite-normalized REE patterns of calcites are highly variable and show generally no systematic correlation with the paragenetic sequence. The oxygen isotope composition of calcites is very homogeneous (?18OVSMOW=24.9±1.1‰, n=34) indicating crystallization temperatures of less than 100 °C. Carbon isotope values of calcites show a considerable variation ranging from -18.7 to -2.9‰ (VPDB). The 87Sr/86Sr ratio of calcites varies between 0.706 and 0.708 and is more radiogenic than that of the host basalt (~0.705). The most likely source of silica, calcium, carbon, and minor elements in the infill of the geodes is the highly reactive interstitial glass of the host basalts leached by gas-poor aqueous solutions of meteoric origin ascending from the locally artesian Botucatú aquifer system in the footwall of the volcanic sequence. The genesis of amethyst geodes in basalts at Ametista do Sul, Brazil, is thus considered as a two-stage process with an early magmatic protogeode formation and a late, low temperature infill of the cavity.

  15. Carbon and oxygen isotopes in apatite CO/sub 2/ and co-existing calcite

    SciTech Connect

    Kolodny, Y.; Kaplan, I. R.

    1981-04-01

    Carbon and oxygen isotopes were analyzed in carbonate apatite CO/sub 2/ and in co-existing calcite. Both C and O in apatite CO/sub 2/ are enriched in the respective light isotopes relative to calcite. These results confirm the proposition that carbonate is part of the apatite structure.

  16. Isotopic composition of a calcite-cemented layer in the Lower Jurassic Bridport Sands, southern England: Implications for formation of laterally extensive calcite-cemented layers

    SciTech Connect

    Bjoerkum, P.A. ); Walderhaug, O. )

    1993-07-01

    [delta][sup 18]O[sub PDB] and [delta][sup 13]C[sub PDB] values have been measured on 107 calcite cement samples from a laterally extensive (> 3 km) and continuous calcite-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 calcite-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 calcite-cemented layer. The [delta][sup 18]O[sub PDB] values therefore indicate that the calcite-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 calcite cement in the layer was biogenic carbonate.

  17. Microbially induced calcite precipitation-based sequestration of strontium by Sporosarcina pasteurii WJ-2.

    PubMed

    Kang, Chang-Ho; Choi, Jae-Ho; Noh, JunGu; Kwak, Dae Young; Han, Sang-Hyun; So, Jae-Seong

    2014-12-01

    Contamination by radioactive strontium ((90)Sr) is a significant environmental problem. Ureolytically driven calcium carbonate precipitation has been proposed for use in geotechnical engineering for soil remediation applications. In this study, 68 ureolytic bacterial strains were newly isolated from various environments. Of these, 19 strains were selected based on ureolytic activity shown when cultured on urea agar plates and identified through 16S rRNA gene sequencing. From these selected strains, Sporosarcina pasteurii WJ-2 (WJ-2) was selected for subsequent study. A simple method was developed to determine the effectiveness of microbially induced calcite precipitation (MICP). Unlike any other methods, it does not require advanced skills and sophisticated tools. Using this method, we were able to determine the ability of the bioconsolidated sand to retard the flow of crystal violet through the 25-mL column. Also, MICP by WJ-2 was evaluated for its potential to counteract Sr contamination in column experiments using natural sand. WJ-2-induced precipitation led to successful sequestration of approximately 80 % of the Sr from the soluble fraction of the sand. The utility of MICP in bioremediation was further confirmed through X-ray diffraction, scanning electron microscopy, and inductively coupled plasma mass spectrometry. PMID:25190302

  18. Influence of calcite on uranium(VI) reactive transport in the groundwater–river mixing zone

    SciTech Connect

    Ma, Rui; Liu, Chongxuan; Greskowiak, Janek; Prommer, Henning; Zachara, John M.; Zheng, Chunmiao

    2014-01-23

    Calcite is an important mineral that can affect uranyl reactive transport in subsurface sediments. This study investigated the distribution of calcite 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 calcite concentration as a result of dynamic groundwater-river interactions. The calcite 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 calcite distribution and its concentration dynamics is an important consideration for field characterization, monitoring, and reactive transport prediction.

  19. The quantitative determination of calcite associated with the carbonate-bearing apatites

    USGS Publications Warehouse

    Silverman, Sol R.; Fuyat, Ruth K.; Weiser, Jeanne D.

    1951-01-01

    The CO2 combined as calcite in carbonate-bearing apatites as been distinguished from that combined as carbonate-apatite, or present in some form other than calcite, 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 calcite, but in all the samples an appreciable part of the carbonite content is not present as calcite. 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 calcite entrapped along an internal network of surfaces.

  20. Transformation and Crystallization Energetics of Synthetic and Biogenic Amorphous Calcium Carbonate

    SciTech Connect

    Radha, A. V.; Forbes, Tori Z.; Killian, Christopher E.; Gilbert, P.U.P.A; Navrotsky, Alexandra

    2010-01-01

    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 crystallizes to calcite or aragonite. The energetics of transformation and crystallization 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 crystallization of ACC can follow an energetically downhill sequence: more metastable hydrated ACC ? less metastable hydrated ACC?anhydrous ACC ~ biogenic anhydrous ACC?vaterite ? aragonite ? calcite. In a given reaction sequence, not all these phases need to occur. The transformations involve a series of ordering, dehydration, and crystallization processes, each lowering the enthalpy (and free energy) of the system, with crystallization of the dehydrated amorphous material lowering the enthalpy the most. ACC is much more metastable with respect to calcite 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 crystallizes to calcite. The initial formation of ACC may be a first step in the precipitation of calcite under a wide variety of conditions, including geological CO? sequestration.

  1. Age constraints on fluid inclusions in calcite at Yucca Mountain

    SciTech Connect

    Neymark, Leonid A.; Amelin, Yuri V.; Paces, James B.; Peterman, Zell E.; Whelan, Joseph F.

    2001-04-29

    The {sup 207}Pb/{sup 235}U ages for 14 subsamples of opal or chalcedony layers younger than calcite formed at elevated temperature range between 1.88 {+-} 0.05 and 9.7 {+-} 1.5 Ma with most values older than 6-8 Ma. These data indicate that fluids with elevated temperatures have not been present in the unsaturated zone at Yucca Mountain since about 1.9 Ma and most likely since 6-8 Ma. Discordant U-Pb isotope data for chalcedony subsamples representing the massive silica stage in the formation of the coatings are interpreted using a model of the diffusive loss of U decay products. The model gives an age estimate for the time of chalcedony formation around 10-11 Ma, which overlaps ages of clay minerals formed in tuffs below the water table at Yucca Mountain during the Timber Mountain thermal event.

  2. Seed Treatment. Bulletin 760.

    ERIC Educational Resources Information Center

    Lowery, Harvey C.

    This manual gives a definition of seed treatment, the types of seeds normally treated, diseases and insects commonly associated with seeds, fungicides and insecticides used, types of equipment used for seed treatment, and information on labeling and coloring of treated seed, pesticide carriers, binders, stickers, and safety precautions. (BB)

  3. Toward Molecular Nanowires Self-Assembled on an Insulating Substrate: Heptahelicene-2-carboxylic acid on Calcite (101j4)

    E-print Network

    Kühnle, Angelika

    acid on Calcite (101j4) Philipp Rahe,,§ Markus Nimmrich,,§ Andreas Greuling, Jens Schu¨tte, Irena G) cleavage plane of calcite. The molecule used is racemic heptahelicene-2-carboxylic acid, which forms

  4. Calcite dissolution and Ca/Na ion-exchange reactions in columns with different flow rates through high ESR soil 

    E-print Network

    Navarre, Audrey

    1999-01-01

    -exchange complex. Following elution with deionized water, the columns were sectioned and analyzed for residual Na. In all cases, the eluate exhibited approximate thermodynamic equilibrium with respect to calcite. Calcite dissolution and Na?/Ca²? ion exchange...

  5. Precipitation of Ordered Dolomite via Simultaneous Dissolution of Calcite and Magnesite: New Experimental Insights into an Old

    E-print Network

    Montes-Hernandez, German

    Alpes, ISTerre, F-38041 Grenoble, France § Physics of Geological Processes, University of Oslo, Box 1048. Calcite dolomitization is carried out by placing high-purity calcite or limestone material in contact

  6. Adsorption of As(V), As(III) and methyl arsenic by calcite and the impact of some groundwater species 

    E-print Network

    Jones, Robert Garret

    2009-05-15

    solubility. This study indicates that arsenic adsorption response by calcite was different than that of phosphate suggesting that arsenic may not be specifically adsorbed to calcium at the calcite surface. Reduction and biomethylation of arsenic decreased...

  7. Implications of solution chemistry effects: Direction-specific restraints on the step kinetics of calcite growth

    NASA Astrophysics Data System (ADS)

    Hong, Mina; Teng, H. Henry

    2014-09-01

    Classical crystallization models successfully depict the dependence of growth kinetics on thermodynamic driving force but cannot predict the roles of solution chemistry. Yet, it has become increasingly clear that crystal growth rate at fixed supersaturations depends on pH, ionic strength, and the relative abundance of cations and anions in the parent solutions. We conducted experiments to isolate the effect of individual solution-chemistry parameters on calcite step growth kinetics. Our results revealed a distinct correlation between step velocity and pH in acute and obtuse directions and a simultaneous trend change at pH ?9.5. Step speeds varied with solution stoichiometry, and each direction reached its maximal rate at a different [Ca]/[CO32-] value. In addition, the solution cation/anion at which maximal step speed occurred appeared to be pH dependent as well. Limited effect of ionic strength on step growth was observed in the obtuse direction at low background electrolyte concentrations, but no obvious change was found for growth at the acute side. We proposed a growth model based upon independent incorporation of cations and anions and interpreted these observations as: (1) solute constituents enter kinks through direct solution diffusion at obtuse steps but surface diffusion at acute steps; (2) growth is limited by Ca2+ dehydration at the obtuse side, but by surface adsorption and reorientation and rearrangement of CO32- in the acute direction; and (3) background electrolyte (NaCl in our study) competes with solutes for surface sites at more easily accessible kinks.

  8. Diel cycles in calcite production and dissolution in a eutrophic basin

    SciTech Connect

    Cicerone, D.S.; Stewart, A.J.; Roh, Y.

    1999-10-01

    Calcite 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 calcite production and dissolution. Diel cycles in calcite 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 calcite 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 calcite with Cd, under solid-liquid nonequilibrium conditions. The authors found that the basin accumulated and stored calcite. In situ monitoring showed that calcite was produced during daylight, and tended to dissolve again at night; the calcite 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 calcite, in response to dissolved CO{sub 2} changes. Thus, concentrations of dissolved Cd can vary over daily cycles, mediated by diel changes in calcite production and dissolution. Thermodynamic considerations suggest that other metals, such as Zn, Sr, Ni, and Ba, may demonstrate this behavior as well.

  9. Interactions of arsenic with calcite surfaces revealed by in situ nanoscale imaging

    NASA Astrophysics Data System (ADS)

    Renard, François; Putnis, Christine V.; Montes-Hernandez, German; Ruiz-Agudo, Encarnacion; Hovelmann, Jörn; Sarret, Géraldine

    2015-06-01

    Arsenic dissolved in water represents a key environmental and health challenge because several million people are under the threat of contamination. In calcareous environments calcite may play an important role in arsenic solubility and transfer in water. Arsenic-calcite 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) calcite 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 calcite surface, and XAS results showed that As(V) was mostly incorporated in the calcite structure. For As(III), AFM results showed much less impact on calcite 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 calcite and the resulting calcite contained 36% As(III) and 64% As(V). All these experimental results confirm that As(V) has a much stronger interaction with calcite than As(III) and that calcite may represent an important reservoir for arsenic in various geological environments.

  10. Orientation with a Viking sun-compass, a shadow-stick, and two calcite sunstones under various weather conditions.

    PubMed

    Bernáth, Balázs; Blahó, Miklós; Egri, Adám; Barta, András; Kriska, György; Horváth, Gábor

    2013-09-01

    It is widely accepted that Vikings used sun-compasses to derive true directions from the cast shadow of a gnomon. It has been hypothesized that when a cast shadow was not formed, Viking navigators relied on crude skylight polarimetry with the aid of dichroic or birefringent crystals, called "sunstones." We demonstrate here that a simple tool, that we call "shadow-stick," could have allowed orientation by a sun-compass with satisfying accuracy when shadows were not formed, but the sun position could have reliably been estimated. In field tests, we performed orientation trials with a set composed of a sun-compass, two calcite sunstones, and a shadow-stick. We show here that such a set could have been an effective orientation tool for Vikings only when clear, blue patches of the sky were visible. PMID:24085076

  11. Total immersion crystal growth

    NASA Technical Reports Server (NTRS)

    Morrison, Andrew D. (inventor)

    1987-01-01

    Crystals of wide band gap materials are produced by positioning a holder receiving a seed crystal at the interface between a body of molten wide band gap material and an overlying layer of temperature-controlled, encapsulating liquid. The temperature of the layer decreases from the crystallization temperature of the crystal at the interface with the melt to a substantially lower temperature at which formation of crystal defects does not occur, suitably a temperature of 200 to 600 C. After initiation of crystal growth, the leading edge of the crystal is pulled through the layer until the leading edge of the crystal enters the ambient gas headspace which may also be temperature controlled. The length of the column of liquid encapsulant may exceed the length of the crystal such that the leading edge and trailing edge of the crystal are both simultaneously with the column of the crystal. The crystal can be pulled vertically by means of a pulling-rotation assembly or horizontally by means of a low-angle withdrawal mechanism.

  12. STRONTIUM ISOTOPE EVOLUTION OF PORE WATER AND CALCITE IN THE TOPOPAH SPRING TUFF, YUCCA MOUNTAIN , NEVADA

    SciTech Connect

    B.D. Marshall; K. Futa

    2001-02-07

    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 calcite 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 calcite associated with those fluid inclusions is important in understanding the thermal history of the potential repository site. Calcite 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 calcite 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 calcite associated with specific fluid inclusions is complicated. Calcite is commonly bladed with complex textural relations, and datable opal or chalcedony may be millions of years older or younger than the calcite layer or may be absent from the coating entirely. Therefore, a more direct method of dating the calcite 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 calcite. Although the water that precipitated the calcite 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-rock interaction in the overlying nonwelded and essentially unfractured Paintbrush Group tuffs (PTn). The method of dating secondary minerals from known strontium evolution rates in rocks cannot be used in this study because it assumes the water that deposited the minerals was in isotopic equilibrium with the rock, which is not the case for the pore water in the TSw. Therefore, the evolution of the strontium isotope composition of the water that deposited the calcite, as recorded by the strontium coprecipitated with calcium in the calcite, was used to develop a model for determining the age of the calcite.

  13. JET-SUSPENDED, CALCITE-BALLASTED CYANOBACTERIAL.WATERWARTS IN A tment of Arizona State ,Tempe, USA

    E-print Network

    Farmer, Jack D.

    (2002) JET-SUSPENDED, CALCITE-BALLASTED CYANOBACTERIAL.WATERWARTS IN A DESERT Bman D. tment likely selectedfor both traits. The mechanismsbywhich con- trolled nucleation of extracellular calcite is achieved remain to be explored. Key index words: buoyancy; calcite precipitation; col- ony formation

  14. Origin and distribution of calcite concretions in Cretaceous Wall Creek Member, Wyoming: Reservoir-quality implication for shallow-marine

    E-print Network

    Gani, M. Royhan

    Origin and distribution of calcite concretions in Cretaceous Wall Creek Member, Wyoming: Reservoir in revised form 29 December 2013 Available online Keywords: Calcite concretion Diagenesis Wyoming Reservoir quality Shallow-marine Turonian a b s t r a c t Calcite concretions reduce reservoir quality

  15. True Atomic-Resolution Imaging of (10j14) Calcite in Aqueous Solution by Frequency Modulation Atomic Force Microscopy

    E-print Network

    Kühnle, Angelika

    True Atomic-Resolution Imaging of (10j14) Calcite in Aqueous Solution by Frequency ModulationVed October 16, 2008. ReVised Manuscript ReceiVed January 2, 2009 Calcite (CaCO3) is one of the most abundant stable cleavage plane of calcite under liquid conditions using frequency modulation atomic force

  16. Experimental evidence for kinetic effects on B/Ca in synthetic calcite: Implications for potential B(OH)4

    E-print Network

    Zeebe, Richard E.

    Experimental evidence for kinetic effects on B/Ca in synthetic calcite: Implications for potential a clearer understanding of the B incorporation mechanism, we performed inorganic calcite precipitation experiments using a pH-stat system. As pre- viously reported, we confirm that B/Ca in calcite increases

  17. PII S0016-7037(99)00103-9 Reversed calcite morphologies induced by microscopic growth kinetics: Insight into

    E-print Network

    Dove, Patricia M.

    PII S0016-7037(99)00103-9 Reversed calcite morphologies induced by microscopic growth kinetics investigation of calcite growth quantifies relationships between solution super- saturation and the rates of calcite mineralization have used indirect approaches that monitor compositional changes of growth media

  18. Oriented Growth of Calcite Controlled by Self-Assembled Monolayers of Functionalized Alkanethiols Supported on Gold and

    E-print Network

    Aizenberg, Joanna

    Oriented Growth of Calcite Controlled by Self-Assembled Monolayers of Functionalized Alkanethiols 02138 ReceiVed December 9, 1998 Abstract: This paper describes the oriented nucleation of calcite, and SO3 -/Ag induced the face-selective nucleation of calcite from the (015), (012), (104), (103), (1 0

  19. Porous, Biphasic CaCO3-Calcium Phosphate Biomedical Cement Scaffolds from Calcite (CaCO3) Powder

    E-print Network

    Tas, A. Cuneyt

    Porous, Biphasic CaCO3-Calcium Phosphate Biomedical Cement Scaffolds from Calcite (CaCO3) Powder A. Cuneyt Tas* Department of Biomedical Engineering, Yeditepe University, Istanbul 34755, Turkey Calcite (CaH 3.2 by adding NaOH, to form biphasic, micro-, and macroporous calcite-apatitic calcium phosphate (Ap

  20. Water-Induced Reconstruction that Affects Mobile Ions on the Surface of Calcite Treavor A. Kendall and Scot T. Martin*

    E-print Network

    Water-Induced Reconstruction that Affects Mobile Ions on the Surface of Calcite Treavor A. Kendall-sequenced contact-force micrographs show that the (101h4) calcite cleavage surface reconstructs in humid air through loosely bound water and may therefore be a hydrated calcium carbonate phase stabilized by the calcite

  1. Experimental Optical-quality geological calcite was cleaved into fragments. In situ atomic force microscope (AFM) imaging was

    E-print Network

    Dickinson, J. Thomas

    Experimental Optical-quality geological calcite was cleaved into fragments. In situ atomic force a is the activity of the ionic species and Ksp=10-8.54 is the equilibrium solubility of calcite at zero ionic and lower terraces are good sources of adsorbed ions. In calcite, the diffusion of ions along both terraces

  2. PII S0016-7037(00)00341-0 Kinetics of calcite growth: Surface processes and relationships to macroscopic rate laws

    E-print Network

    Dove, Patricia M.

    PII S0016-7037(00)00341-0 Kinetics of calcite growth: Surface processes and relationships with observations of microscopic surface processes to quantify the dependence of calcite growth on supersaturation Atomic Force Microscopy was used to quantify calcite growth rates and observe transitions in growth

  3. Speleothem calcite farmed in situ: Modern calibration of d18 C paleoclimate proxies in a continuously-monitored

    E-print Network

    Speleothem calcite farmed in situ: Modern calibration of d18 O and d13 C paleoclimate proxies precipitated (low temperature) speleothem calcite is systematically heavier than the d18 O of laboratory-grown calcite for a given temperature. To understand this apparent offset, rainwater, cave drip water

  4. What Are Chia Seeds?

    MedlinePLUS

    ... Men For Women For Seniors What Are Chia Seeds? Published February 05, 2014 Print Email When you ... number of research participants. How to Eat Chia Seeds Chia seeds can be eaten raw or prepared ...

  5. Grape Seed Extract

    MedlinePLUS

    ... Read our disclaimer about external links Menu Grape Seed Extract Common Name: grape seed extract Latin Name: Vitis vinifera On this page: ... This fact sheet provides basic information about grape seed extract—common names, what the science says, potential ...

  6. Fabrication and Characterization of (100),(001)-Oriented Reduction-Resistant Lead-Free Piezoelectric (Ba,Ca)TiO3 Ceramics Using Platelike Seed Crystals

    NASA Astrophysics Data System (ADS)

    Ichikawa, Hiroki; Sakamoto, Wataru; Akiyama, Yoshikazu; Maiwa, Hiroshi; Moriya, Makoto; Yogo, Toshinobu

    2013-09-01

    The preparation of reduction-resistant (Ba,Ca)TiO3 ceramics as lead-free piezoelectric materials was studied. To improve their electrical properties, (100),(001)-oriented (Ba0.85Ca0.15)TiO3 ceramics were fabricated by the reactive templated grain growth method using a mixture of platelike CaTiO3 and BaTiO3 particles. The platelike CaTiO3 and BaTiO3 particles were prepared through a topochemical microcrystal conversion process using CaBi4Ti4O15 and BaBi4Ti4O15 plate-like precursor crystals. The 100 orientation degree of the grain-oriented (Ba0.85Ca0.15)TiO3 ceramics was 92%, as estimated by Lotgering's equation. In addition, 1 mol % Ba excess and 1 mol % Mn-doped (Ba0.85Ca0.15)TiO3 sintered bodies, which were sintered at 1350 °C in an Ar flow containing H2 (0.3%), had sufficient resistivity to allow the characterization of electrical properties. The ferroelectric and field-induced strain properties of the (Ba0.85Ca0.15)TiO3 ceramics, sintered in the reducing atmosphere, were markedly improved as a result of fabricating grain-oriented samples. The field-induced strain coefficient (estimated from the slope of the unipolar strain loop) of the nonreducible (100),(001)-oriented (Ba0.85Ca0.15)TiO3 ceramics reached 570 pm/V, which was higher than that of polycrystals (260 pm/V) with no preferential orientation.

  7. The surface reactivity of chalk (biogenic calcite) with hydrophilic and hydrophobic functional groups

    NASA Astrophysics Data System (ADS)

    Okhrimenko, D. V.; Dalby, K. N.; Skovbjerg, L. L.; Bovet, N.; Christensen, J. H.; Stipp, S. L. S.

    2014-03-01

    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 calcite. 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 calcite 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 crystals 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 calcite 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 chalk surfaces and partly by adsorbed organic material. GS < GS after extraction < WS < WS after extraction < Ålborg after extraction ? Ålborg. The increase of spreading work for WS chalk for ethanol is 21 mN/m and for water is 26 mN/m, a ratio of 21/26 = 0.81. The increase of spreading work for GS chalk for ethanol and water are 36 and 42 mN/m, a ratio of 36/42 = 0.86. The similarity between these ratios leads us to conclude, that the surface that was produced by extraction of the organic material is quite similar for these two samples.The total surface energy increase, after the extraction of organics, for GS and WS was 67 and 49 mJ/m2. Further separation of surface energy into polar and dispersive parts showed that, for both samples, removing organic matter by extraction preferably increases the dispersive component of the surface energy. The contribution from dispersive surface energy to the increase in total surface energy was 87% for GS and 73% for WS chalk. A high relative proportion of dispersive component in the total surface energy is also typical for clay minerals (Chassin et al., 1986; Jouany and Chassin, 1987; Kádár et al., 2006).This demonstrates that the additional adsorption sites that are exposed by the extraction procedure are less polar than the sites originally exposed. Based on these results, we can conclude that chalk particles have surface sites of different polarity and that organic compounds preferentially adsorb at the less polar sites. These additional sites have quite similar surface properties for both North Sea chalk samples with an energy distribution that is similar to clays, that are described in the literature (Chassin et al., 1986; Jouany and Chassin, 1987; Kádár et al., 2006).The Ålborg chalk initially has minimal adsorbed organic material and the work of wetting changes very little after the treatment for extracting organic material. Considering the lower reproducibility of the results on Ålborg chalk, the differences in surface energies before and after extraction are considered insignificant and

  8. Crystallization of Macromolecules

    PubMed Central

    Friedmann, David; Messick, Troy; Marmorstein, Ronen

    2014-01-01

    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 crystallization 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 crystallization trials is then described, along with a protocol for confirming whether the crystals obtained are composed of macromolecule as opposed to a crystallization reagent . Next, the optimization of crystallization conditions is presented. Finally, protocols that facilitate the growth of larger crystals through seeding are described. PMID:22045560

  9. Fabrication of porous calcite using chopped nylon fiber and its evaluation using rats.

    PubMed

    Ishikawa, Kunio; Tram, Nguyen Xuan Thanh; Tsuru, Kanji; Toita, Riki

    2015-02-01

    Although porous calcite has attracted attention as bone substitutes, limited studies have been made so far. In the present study, porous calcite 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 calcite without forming CaO. Macro- and micro-porosities of the porous calcite were approximately 23 and 16%, respectively. Diameter of the macropores was approximately 100 ?m which is suitable for bone tissue penetration. Porous calcite 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 calcite. Furthermore, bone tissue penetrated interior to the macropore at 8 weeks. These results demonstrated the good potential value of porous calcite as artificial bone substitutes. PMID:25649514

  10. Direct nanoscale observations of the coupled dissolution of calcite and dolomite and the precipitation of gypsum

    PubMed Central

    Cama, Jordi; Soler, Josep Maria; Putnis, Christine V

    2014-01-01

    Summary In-situ atomic force microscopy (AFM) experiments were performed to study the overall process of dissolution of common carbonate minerals (calcite 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 calcite. The calculated dissolution rates of calcite 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 calcite dissolution showed short gypsum nucleation induction times. The gypsum precipitate quickly coated the calcite surface, forming arrow-like forms parallel to the crystallographic orientations of the calcite etch pits. Gypsum precipitation coupled with dolomite dissolution was slower than that of calcite, 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

  11. Method of controlling defect orientation in silicon crystal ribbon growth

    NASA Technical Reports Server (NTRS)

    Leipold, M. H. (inventor)

    1978-01-01

    The orientation of twinning and other effects in silicon crystal ribbon growth is controlled by use of a starting seed crystal having a specific (110) crystallographic plane and (112) crystallographic growth direction.

  12. Structure of supersaturated solution and crystal nucleation induced by diffusion

    NASA Astrophysics Data System (ADS)

    Ooshima, Hiroshi; Igarashi, Koichi; Iwasa, Hideo; Yamamoto, Ren

    2013-06-01

    The effect of a seed crystal on nucleation of L-alanine from a quiescent supersaturated solution was investigated. When a seed crystal was not used, nucleation did not occur at least for 5 h. When a seed crystal was introduced into the supersaturated solution with careful attention to avoid convection of the solution, fine crystals appeared at the place far from the seed crystal. At that time, there was no convection at the place that fine crystals appeared. Namely, there was no possibility that those fine crystals came from the surface of seed crystal. We supposed that nucleation was induced by directional diffusion of solute molecules caused by growth of the seed crystal. 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 seed crystals. 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 crystals induces nucleation.

  13. Activators of photoluminescence in calcite: evidence from high-resolution, laser-excited luminescence spectroscopy

    USGS Publications Warehouse

    Pedone, V.A.; Cercone, K.R.; Burruss, R.C.

    1990-01-01

    Laser-excited luminescence spectroscopy of a red-algal, biogenic calcite and a synthetic Mn-calcite can make the distinction between organic and trace-element activators of photoluminescence. Organic-activated photoluminescence in biogenic calcite 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.

  14. Seeding Rangeland 

    E-print Network

    Welch, Tommy G.; Hafercamp, Marshall R.

    2001-01-04

    , shredding or use of herbicides may be necessary during the first growing season to allow seeded spe- cies to become established. Most grass seedlings can tolerate a herbicide application after the seedlings have reached the fourth leaf stage. 3 xx x x xxx x... xx x x x xx x x xxx x xx x x x x x xx x xxx x xx x x x xxx x I I I I x x xx x x xxx x x x xxx I I I xx Xx xxx xxx x x xx x x x x xx xx x x I x Xx xxx x x x x I I I x xx . 6 .? -. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 LEGEND Trans-Pecos High...

  15. Using neutrons to investigate changes in strain partitioning between the phases during plastic yielding of calcite+halite composites

    NASA Astrophysics Data System (ADS)

    Covey-Crump, S. J.; Schofield, P. F.; Daymond, M. R.

    2006-11-01

    We have performed several room pressure and temperature uniaxial compression experiments on synthetic calcite+halite composites on the ENGIN-X beamline at the ISIS facility, UK, with a view to using the penetrating power of neutrons to monitor how strain partitioning between these phases changes as the halite undergoes plastic yielding. The principal dataset comes from samples for which the two phases were randomly intermixed but in which the volume fractions of the phases varied from 10 to 90% calcite. For samples with less than about 50% calcite, the strain partitioning between the phases was unaffected by halite yielding, but at higher calcite contents, load transfer from the halite to the calcite was initiated when the former yielded. The calcite deformed elastically but at high calcite contents (>80%) there was a switch from approximately homogeneous stress to homogeneous strain deformation within that phase.

  16. Ultrasonic Observation of the Calcite-Aragonite Transition

    NASA Technical Reports Server (NTRS)

    Ahrens, T. J.; Katz, S.

    1963-01-01

    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 calcite-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.

  17. Alkaline flocculation of Phaeodactylum tricornutum induced by brucite and calcite.

    PubMed

    Vandamme, Dries; Pohl, Philip I; Beuckels, Annelies; Foubert, Imogen; Brady, Patrick V; Hewson, John C; Muylaert, Koenraad

    2015-11-01

    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 (>7.5mM). Zeta potential measurements suggest that brucite precipitation caused flocculation by charge neutralization. When calcium concentration was 12.5mM, flocculation was also observed at a pH of 10. Zeta potential remained negative up to pH 11.5, suggesting that precipitated calcite caused flocculation by a sweeping coagulation mechanism. PMID:26310384

  18. Control of carbonate alkalinity on Mg incorporation in calcite: Insights on the occurrence of high Mg calcites in diagenetic environments

    NASA Astrophysics Data System (ADS)

    Purgstaller, Bettina; Mavromatis, Vasileios; Dietzel, Martin

    2015-04-01

    High Mg calcites (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 calcite lattice seems to be favored by intensive supply of carbonate ions as observed in AOM originated HMC in early diagenetic sediments.

  19. Seed health and vigor

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The health of lentil and chickpea seed greatly impacts the quality of the crop stand and yield. Healthy seed has a high germination rate, is whole (free of cracks or other damage), is free from foreign matter including weed seed and has limited seedborne pathogens. The health of the seed often dep...

  20. Simulation of calcite dissolution and porosity changes in saltwater mixing zones in coastal aquifers

    USGS Publications Warehouse

    Sanford, W.E.; Konikow, L.F.

    1989-01-01

    Thermodynamic models of aqueous solutions have indicated that the mixing of seawater and calcite-saturated fresh groundwater can produce a water that is undersaturated with respect to calcite. 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 calcite 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 calcite. -from Authors

  1. Calcium sulfoaluminate (Ye'elimite) hydration in the presence of gypsum, calcite, and vaterite

    SciTech Connect

    Hargis, Craig W.; Telesca, Antonio; Monteiro, Paulo J.M.

    2014-11-15

    Six calcium sulfoaluminate-based cementitious systems composed of calcium sulfoaluminate, calcite, 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 calcite 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 calcite 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 calcite.

  2. The Influence of Equilibrium Reactions on the Kinetics of Calcite Dissolution in Lactic Acid Solutions 

    E-print Network

    Shedd, Daniel C

    2014-08-07

    acid and calcite will allow for optimized treatment design. The kinetic model was also used to isolate the contributions of the transport of reactants, the surface reaction, and the transport of products to the overall resistance of the reaction...

  3. High School Forum: "Invitations to Enquiry": The Calcite/Acid Reaction.

    ERIC Educational Resources Information Center

    Herron, J. Dudley, Ed.; Driscoll, D. R.

    1979-01-01

    Describes a high school chemistry experiment which involves the reaction between calcite and hydrochloric and sulfuric acids. This reaction can be carried out as a projected demonstration and on an individual basis. (HM)

  4. Release equation of state of dry and water-saturated porous calcite

    SciTech Connect

    Grady, D.E.; Moody, R.L.; Drumheller, D.S.

    1986-11-01

    Equation of state data on calcite obtained from shock compression and release wave experiments are reported. Powder gun and two-stage gun impact technology along with time-resolved velocity interferometry, are used to produce and measure planar shock and release wave states. Experiments are performed on crystalline calcite and on dry- and water-saturated porous calcite at shock pressures ranging from 10 to 66 GPa. Developmental work required to perform high-pressure shock -wave experiments on porous samples with the two-stage gas gun is described. Lagrangian analysis methods are used to determine pressure-density release paths from measured wave profiles. A high-pressure phase change in calcite has been identified from the release-wave data. Calculational results obtained using a model based on a theory of immiscible mixture are compared with the experimental data.

  5. Phase transformation of Mg-calcite to aragonite in active-forming hot spring travertines

    NASA Astrophysics Data System (ADS)

    Greer, Heather F.; Zhou, Wuzong; Guo, Li

    2015-08-01

    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 calcite 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 calcite and therefore instigated the phase transformation of the core of the rhombohedral calcite particles to an aragonite phase with a higher crystallinity. The single crystalline aragonite microrods with a higher density than the Mg-calcite 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.

  6. The Influence of Exotic Calcite on the Mechanical Behavior of Quartz Bearing Fault Gouge

    NASA Astrophysics Data System (ADS)

    Carpenter, B. M.; Di Stefano, G.; Collettini, C.

    2014-12-01

    The interseismic recovery of frictional strength is a fundamental part of the seismic cycle. This restrengthening, and related phenomena, plays a key role in determining the stability and mode of tectonic faulting. Recent experimental data has shown that gouge mineralogy has a strong influence on the rate of frictional healing, with calcite-dominated gouges showing the highest rates. Combining these data with widespread observations of calcite as cement or veins in non-carbonate hosted faults, indicates that the presence of calcite within a fault gouge could play an important role in shallow- and mid-crustal earthquakes. We report on laboratory experiments designed to explore the mechanical behavior of quartz/calcite mixtures as a means to better understand the evolution of fault behavior in faults where carbonate materials are present. We sheared mixtures of powdered Carrara marble (>98% CaCO3) and disaggregated Ottawa sand (99.8% SiO2) at constant normal stress of 5 MPa under saturated conditions at room temperature. We performed slide-hold-slide tests, 1-3,000 seconds, and velocity stepping tests, 0.1-1000 ?m/s, to measure the amount of frictional healing and velocity dependence of friction respectively. Small subsets of experiments were conducted at different boundary conditions. Preliminary results show that the presence of calcite in quartz-based fault gouge has a hardening effect, both in overall frictional strength, where the strength of our mixtures increases with increasing calcite content, and in single experiments, where mixtures with low percentages of calcite show a consistent strain-hardening trend. We also observe that the rates of frictional healing and creep relaxation increase with increasing calcite content. Finally, our results show that the addition of as little as 2.5% calcite within a fault gouge results in a 30% increase in the rate of frictional healing, with further increases in calcite content resulting in larger increases in the rate of healing. Combined with our previous work, our results show that the presence of calcite in fault gouge can lead to accelerated frictional healing and velocity-weakening frictional behavior, favoring seismicity at shallow crustal conditions where faults are thought to fail mostly by aseismic creep.

  7. The Influence of Calcite on The Mechanical Behavior of Quartz-Bearing Gouge

    NASA Astrophysics Data System (ADS)

    Carpenter, Brett; Di Stefano, Giuseppe; Collettini, Cristiano

    2015-04-01

    Mechanical heterogeneities along faults can result in diverse and complex fault slip. These heterogeneities can vary spatially and temporally and may result from changes in fault structure or frictional properties. The accumulation of calcite in non-carbonate faults, via cementation or entrainment, is likely to alter the frictional properties of that fault gouge. Furthermore, widespread observations of calcite as cement, veins, or cataclasites in non-carbonate hosted faults indicates that calcite is readily available and could play an important role during fault reactivation at shallow- and mid-crustal earthquakes. We report on laboratory experiments designed to explore the mechanical behavior of quartz/calcite mixtures as a means to better understand the evolution in behavior of quartz-bearing gouge in the presence of exotic calcite. We sheared mixtures of powdered Carrara marble (>98% CaCO3) and disaggregated Ottawa sand (99.8% SiO2) at constant normal stresses of 5 and 50 MPa under saturated conditions at room temperature. We performed slide-hold-slide tests, 1-3,000 seconds, and velocity stepping tests, 0.1-1000 µm/s, to measure the amount of frictional healing and velocity dependence of friction respectively. At low normal stress, the addition of calcite to quartz-based synthetic fault gouge results in increases in the steady-state frictional strength, and rates of frictional healing and creep relaxation of the gouge. In particular, with the addition of as little as 2.5 wt% calcite, the frictional healing rate increases by 30%. Microstructural observations indicate that shear is accommodated by distributed deformation throughout the gouge layer and that calcite undergoes significantly more comminution compared to quartz. Large quartz grains frequently show minor rounding of angular edges with fine-grained calcite often penetrating fractures. The in-situ addition of calcite to fault gouge, by either the circulation of fluids or the involvement of carbonate rocks in faulting, could lead to significant and progressive changes in fault behavior, i.e. the fault could be frictionally stronger, heal/seal faster, and be more frictionally unstable. At shallow crustal conditions, increased temperature and the concentration of fine-grained calcite along shear surfaces would result in the amplification of the observed behaviors.

  8. Rheological Properties and Reaction Kinetics of Amidoamine Oxide Surfactants-based Acids with Calcite 

    E-print Network

    Li, Lingling

    2012-07-16

    PROPERTIES AND REACTION KINETICS OF AMIDOAMINE OXIDE SURFACTANT-BASED ACIDS WITH CALCITE A Dissertation by LINGLING LI Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements... for the degree of DOCTOR OF PHILOSOPHY May 2011 Major Subject: Petroleum Engineering Rheological Properties and Reaction Kinetics of Amidoamine Oxide Surfactant-based Acids with Calcite Copyright 2011...

  9. Nonhydrostatic effects in stress-wave induced phase transformation of calcite

    SciTech Connect

    Grady, D.E.

    1983-01-01

    Displacive phase transformation occurs readily under stress-wave loading and is dependent on the nonhydrostatic stress state. Both static and stress-wave data for phase transformation in calcite rock are compared for shear stress dependence. A nonhydrostatic thrmodynamic theory has been developed. Through the theory, nonhydrostatic relations of phase equilibria are obtained which constrain the volume and shape change through the transformation. The theory is applied to the stress-induced displacive calcite I-II phase change in Oakhall limestone.

  10. Origin of sulfate in barite and calcite cements in the Jebel Madar salt dome (Oman)

    NASA Astrophysics Data System (ADS)

    Vandeginste, V.; John, C. M.; Gilhooly, W. P.

    2012-12-01

    Jebel Madar is a 500-m high mountain rising in the desert at the Oman Foothills. The Jebel consists of Triassic to Cretaceous carbonate host rocks forming the carapace of a salt dome. Halokinesis caused major fracturing and faulting at Jebel Madar, and the resulting structures acted as the main pathways for fluids that generated diagenetic cements composed of both barite and calcite. The spatial distribution of calcite and barite occurrences shows that calcite is formed in large abundance along the three main faults, whereas barite is more concentrated along faults further away from the three main ones. The stable carbon and oxygen isotope composition of calcite and fluid inclusion data from both calcite and barite show a distinct evolution of the fluid with a highly saline component towards more mixing with meteoric water. This is in agreement with clumped isotopes data on calcite cements indicating an evolution towards lower temperatures, consistent with doming of the Jebel and greater input of lower-temperature descending meteoric fluids. Here, we present sulphur and oxygen isotopic data on barite that suggest a link between the barite formation and the Precambrian salt underlying Jebel Madar. The average ?34S measured in barite is 33‰ CDT (1? = 5‰; n = 33), which falls at the lower end of the ?34S range reported for the Ara Group anhydrite. The average ?18O in the same barite samples is 23‰ VSMOW (1? = 2‰; n = 33). Data from the barite will be compared with sulphur isotopes from the carbonate-associate sulfate in the calcite cements. The overall goal of our research is to gain a better insight in the formation process of barite and calcite in Jebel Madar and its link with salt tectonics. We would like to acknowledge the financial support of QCCSRC (funded jointly by Qatar Petroleum, Shell and the Qatar Science & Technology Park) and the GSA Laubach fund for this study.

  11. Experimental study of the mechanism of the calcite-dolomite replacement

    NASA Astrophysics Data System (ADS)

    Moraila-Martinez, Teresita; Dunkel, Kristina G.; Putnis, Andrew; Putnis, Christine V.

    2014-05-01

    When a mineral comes into contact with a fluid with which it is out of equilibrium, it may be replaced by a phase with a different composition and crystal structure. The reaction mechanism generally involves a coupled dissolution and precipitation mechanism and may result in a pseudomorphic replacement (Putnis, 2009). The existence of sharp limestone-dolomite contacts in natural rocks suggests that this process may operate in the course of dolomitization during burial and diagenesis. The idealized mass balance reaction is generally written as 2CaCO3+Mg2+?CaMg(CO3)2+Ca2+. However, the mechanism and environmental settings of dolomitization, are still under discussion. In order to explore the mechanism of replacement of calcite by dolomite, we performed hydrothermal experiments on marble cubes (Carrara, Italy) of different edge lengths (1.5 to 5 mm), which reacted with (Ca,Mg)Cl2 solutions of varying compositions, at temperatures between 160 and 200 °C for different duration times. The product phases were identified by X-ray diffraction (XRD), Raman spectroscopy, and electron microprobe analysis (EMPA), and the textural evolution was studied by scanning electron microscopy (SEM). The results show that the amount and type of reaction strongly depend on the Mg/Ca ratio, the fluid/rock ratio, the temperature, and the reaction time. Depending on the solution composition, the reaction rims of the marble cubes are made up of several layers containing dolomite with varying textures and porosities as well as magnesite, MgCO3, in the outer rim. Fluid and mass transport along the grain boundaries controls the overall textural evolution and rate of dolomitization. The replacement reactions are pseudomorphic and take place by a coupled dissolution-precipitation mechanism. Putnis A. Mineral Replacement Reactions. In: Thermodynamics and Kinetics of Water-Rock Interaction. Oelkers E. H & Schott J (eds). Reviews in Mineralogy & Geochemistry 30, 87-124 (2009)

  12. Estimation of past seepage volumes from calcite distribution in the Topopah Spring Tuff, Yucca Mountain, Nevada

    USGS Publications Warehouse

    Marshall, B.D.; Neymark, L.A.; Peterman, Z.E.

    2003-01-01

    Low-temperature calcite and opal record the past seepage of water into open fractures and lithophysal cavities in the unsaturated zone at Yucca Mountain, Nevada, site of a proposed high-level radioactive waste repository. Systematic measurements of calcite and opal coatings in the Exploratory Studies Facility (ESF) tunnel at the proposed repository horizon are used to estimate the volume of calcite at each site of calcite and/or opal deposition. By estimating the volume of water required to precipitate the measured volumes of calcite in the unsaturated zone, seepage rates of 0.005 to 5 liters/year (l/year) are calculated at the median and 95th percentile of the measured volumes, respectively. These seepage rates are at the low end of the range of seepage rates from recent performance assessment (PA) calculations, confirming the conservative nature of the performance assessment. However, the distribution of the calcite and opal coatings indicate that a much larger fraction of the potential waste packages would be contacted by this seepage than is calculated in the performance assessment.

  13. Mixing-induced calcite precipitation and dissolution kinetics in micromodel experiments.

    SciTech Connect

    Valocchi, Albert J.; Dewers, Thomas A.; Dehoff, Karl; Yoon, Hongkyu; Werth, Charles J.

    2010-12-01

    Dissolved CO2 from geological CO2 sequestration may react with dissolved minerals in fractured rocks or confined aquifers and cause mineral precipitation. The overall rate of reaction can be limited by diffusive or dispersive mixing, and mineral precipitation can block pores and further hinder these processes. Mixing-induced calcite precipitation experiments were performed by injecting solutions containing CaCl2 and Na2CO3 through two separate inlets of a micromodel (1-cm x 2-cm x 40-microns); transverse dispersion caused the two solutions to mix along the center of the micromodel, resulting in calcite precipitation. The amount of calcite precipitation initially increased to a maximum and then decreased to a steady state value. Fluorescent microscopy and imaging techniques were used to visualize calcite precipitation, and the corresponding effects on the flow field. Experimental micromodel results were evaluated with pore-scale simulations using a 2-D Lattice-Boltzmann code for water flow and a finite volume code for reactive transport. The reactive transport model included the impact of pH upon carbonate speciation and calcite dissolution. We found that proper estimation of the effective diffusion coefficient and the reaction surface area is necessary to adequately simulate precipitation and dissolution rates. The effective diffusion coefficient was decreased in grid cells where calcite precipitated, and keeping track of reactive surface over time played a significant role in predicting reaction patterns. Our results may improve understanding of the fundamental physicochemical processes during CO2 sequestration in geologic formations.

  14. NMR characterization of hydrocarbon adsorption on calcite surfaces: A first principles study

    SciTech Connect

    Bevilaqua, Rochele C. A.; Miranda, Caetano R.; Rigo, Vagner A.; Veríssimo-Alves, Marcos

    2014-11-28

    The electronic and coordination environment of minerals surfaces, as calcite, are very difficult to characterize experimentally. This is mainly due to the fact that there are relatively few spectroscopic techniques able to detect Ca{sup 2+}. Since calcite is a major constituent of sedimentary rocks in oil reservoir, a more detailed characterization of the interaction between hydrocarbon molecules and mineral surfaces is highly desirable. Here we perform a first principles study on the adsorption of hydrocarbon molecules on calcite surface (CaCO{sub 3} (101{sup ¯}4)). The simulations were based on Density Functional Theory with Solid State Nuclear Magnetic Resonance (SS-NMR) calculations. The Gauge-Including Projector Augmented Wave method was used to compute mainly SS-NMR parameters for {sup 43}Ca, {sup 13}C, and {sup 17}O in calcite surface. It was possible to assign the peaks in the theoretical NMR spectra for all structures studied. Besides showing different chemical shifts for atoms located on different environments (bulk and surface) for calcite, the results also display changes on the chemical shift, mainly for Ca sites, when the hydrocarbon molecules are present. Even though the interaction of the benzene molecule with the calcite surface is weak, there is a clearly distinguishable displacement of the signal of the Ca sites over which the hydrocarbon molecule is located. A similar effect is also observed for hexane adsorption. Through NMR spectroscopy, we show that aromatic and alkane hydrocarbon molecules adsorbed on carbonate surfaces can be differentiated.

  15. Multiple origins for zoned cathodoluminescent and noncathodoluminescent calcite cements in Pennsylvanian limestones

    SciTech Connect

    Goldstein, R.H.; Anderson, J.E.; Phares, R.A. )

    1991-03-01

    Noncathodoluminescent calcite containing brightly to moderately luminescent zones is a common early cement in limestones. Three such cements in Upper Pennsylvanian limestones from different areas were studied. All three units are overlain up-section by Permian evaporites and consist of carbonate-siliciclastic 'cyclothems' in which individual cycles were subject to subaerial exposure. With such similar settings, one might predict that petrographically similar calcite cements would have similar origins. In the Holder Formation (New Mexico), the zoned calcite predates compaction, and cross-cutting relationships with cycle-capping paleosols show that zoned cements precipitated during 15 events of subaerial exposure. Therefore, cements precipitated from freshwater during early and repeated subaerial exposure. For the Lansing-Kansas City groups in northwestern Kansas, the zoned calcite cements commonly are among the first precipitated but may postdate some compaction. All-liquid fluid inclusions indicated precipitation below about 50C, from brines of approximately 23 weight %. NaCl equivalent. The brines may have refluxed downward during deposition of Permian evaporites. A limestone of the Lansing-Kansas City groups of west-central Kansas contains early zoned calcite cement that predates compaction. The cement contains all-liquid fluid inclusions indicating precipitation below about 50C. The presence of nonluminescent calcite containing bright subzones is not indicative of a single diagenetic environment. Petrographically similar cements from similar settings may originate in markedly different diagenetic environments.

  16. NMR characterization of hydrocarbon adsorption on calcite surfaces: a first principles study.

    PubMed

    Bevilaqua, Rochele C A; Rigo, Vagner A; Veríssimo-Alves, Marcos; Miranda, Caetano R

    2014-11-28

    The electronic and coordination environment of minerals surfaces, as calcite, are very difficult to characterize experimentally. This is mainly due to the fact that there are relatively few spectroscopic techniques able to detect Ca(2+). Since calcite is a major constituent of sedimentary rocks in oil reservoir, a more detailed characterization of the interaction between hydrocarbon molecules and mineral surfaces is highly desirable. Here we perform a first principles study on the adsorption of hydrocarbon molecules on calcite surface (CaCO3 (101¯4)). The simulations were based on Density Functional Theory with Solid State Nuclear Magnetic Resonance (SS-NMR) calculations. The Gauge-Including Projector Augmented Wave method was used to compute mainly SS-NMR parameters for (43)Ca, (13)C, and (17)O in calcite surface. It was possible to assign the peaks in the theoretical NMR spectra for all structures studied. Besides showing different chemical shifts for atoms located on different environments (bulk and surface) for calcite, the results also display changes on the chemical shift, mainly for Ca sites, when the hydrocarbon molecules are present. Even though the interaction of the benzene molecule with the calcite surface is weak, there is a clearly distinguishable displacement of the signal of the Ca sites over which the hydrocarbon molecule is located. A similar effect is also observed for hexane adsorption. Through NMR spectroscopy, we show that aromatic and alkane hydrocarbon molecules adsorbed on carbonate surfaces can be differentiated. PMID:25429955

  17. Co-Precipitation of Trace Metals in Groundwater & Vadose Zone Calcite: In Situ Containment & Stabilization of Strontium-90 & Other Divalent Metals & Radionuclid

    SciTech Connect

    Ferris, F. Grant

    2003-06-01

    A suite of experiments were performed to investigate the partitioning of Sr2+ (to mimic the radionuclide 90Sr) between calcite and artificial groundwater in response to the hydrolysis of urea by Bacillus pasteurii under conditions that simulate in-situ aquifer conditions. Experiments were performed at 10, 15 and 20 C over 7 days in microcosms inoculated with B. pasteurii ATCC 11859 and containing an artificial groundwater and urea (AGW), and an AGW including a Sr contaminant treatment. During the experiments ammonium concentration from bacterial urea hydrolysis increased asymptotically, and derived rate constants (kurea) that were between 13 and 10 times greater at 20 C, than at 15 and 10 C. Calcite precipitation was initiated after similar amounts of urea had been hydrolysed ({approx} 4.0 mmoles L-1) and a similar critical saturation state (mean Scritical = 53, variation = 20%) had been reached, independent of temperature and Sr treatment. Because of the positive relationship between urea hydrolysis rate and temperature, precipitation began by the end of day 1 at 20 C, and between days 1 and 2 at 15 and 10 C. The rate of calcite precipitation increased with, and was fundamentally controlled by S, irrespective of temperature, which connects the dissimilar patterns of urea hydrolysis and dissolved concentrations which are exhibited at the different experiments. The presence of Sr slightly slowed calcite precipitation rates at equivalent values of S, which may reflect the screening of active nucleation and crystal growth sites by Sr. Instantaneous heterogeneous partitioning coefficients (DSr) exhibited a positive association with calcite precipitation rates, but were greater at higher experimental temperatures at equivalent precipitation rates (20 C mean = 0.46; 15 C mean = 0.24; 10 C mean = 0.29). This is likely to reflect the large ionic radius of the Sr ion, which cannot fully co-ordinate relative to ions smaller than Ca at equilibrium conditions, but i s increasingly co-precipitated as all ions are indiscriminately incorporated at higher precipitation rates. The temperature dependence is likely to reflect the higher miscibility of ions in minerals, commonly observed in geochemical systems at higher temperatures.

  18. Synthesis and characterization of Cu3(BTC)2 membranes by thermal spray seeding and secondary growth.

    PubMed

    Noh, Seung-Jun; Kwon, Hyuk Taek; Kim, Jinsoo

    2013-08-01

    Crack-free Cu3(BTC)2 membranes were successfully prepared by thermal spray seeding and secondary growth method. Thermal spray seeding method, combining thermal seeding and pressurized spraying, uniformly distributed seed solution on the support, anchoring seed crystals tightly on the support. After secondary growth of the seeded support in the autoclave, continuous crack-free membrane was obtained by controlling cooling and drying steps. The gas permeation test was conducted at various temperatures using H2, CO2, CH4 and N2 gases. PMID:23882815

  19. Calcite Fluid Inclusion, Paragenetic, and Oxygen Isotopic Records of Thermal Event(s) at Yucca Mountain, Nevada

    SciTech Connect

    B. Peterman; R. Moscati

    2000-08-10

    Yucca Mountain, Nevada, is under consideration as a potential high-level radioactive waste repository situated above the water table in 12.7 Ma tuffs. A wealth of textural and geochemical evidence from low-temperature deposits of calcite and silica, indicates that their genesis is related to unsaturated zone (UZ) percolation and that the level of the potential repository has never been saturated. Nonetheless, some scientists contend that thermal waters have periodically risen to the surface depositing calcite and opal in the tuffs and at the surface. This hypothesis received some support in 1996 when two-phase fluid inclusions (FIs) with homogenization temperatures (Th) between 35 and 75 C were reported from UZ calcite. Calcite deposition likely followed closely on the cooling of the tuffs and continues into the present. The paragenetic sequence of calcite and silica in the UZ is early stage calcite followed by chalcedony and quartz, then calcite with local opal during middle and late stages. Four types of FIs are found in calcite assemblages: (1) all-liquid (L); (2) all-vapor (V); (3) 2-phase with large and variable V:L ratios; and (4) a few 2-phase with small and consistent V:L ratios. Late calcite contains no FI assemblages indicating elevated depositional temperatures. In early calcite, the Th of type 4 FIs ranges from {approx} 40 to {approx} 85 C. Such temperatures (sub-boiling) and the assemblage of FIs are consistent with deposition in the UZ. Some delta 18O values < 10 permil in early calcite support such temperatures. Type 4 FIs, however, seem to be restricted to the early calcite stage, during which either cooling of the tuffs or regional volcanism were possible heat sources. Nonetheless, at present there is no compelling evidence of upwelling water as a source for the calcite/opal deposits.

  20. The role of disseminated calcite in the chemical weathering of granitoid rocks

    USGS Publications Warehouse

    White, A.F.; Bullen, T.D.; Vivit, D.V.; Schulz, M.S.; Clow, D.W.

    1999-01-01

    Accessory calcite, present at concentrations between 300 and 3000 mg kg-1, occurs in fresh granitoid rocks sampled from the Merced watershed in Yosemite National Park, CA, USA; Loch Vale in Rocky Mountain National Park CO USA; the Panola watershed, GA USA; and the Rio Icacos, Puerto Rico. Calcite occurs as fillings in microfractures, as disseminated grains within the silicate matrix, and as replacement of calcic cores in plagioclase. Flow-through column experiments, using de-ionized water saturated with 0.05 atm. CO2, produced effluents from the fresh granitoid rocks that were dominated by Ca and bicarbonate and thermodynamically saturated with calcite. During reactions up to 1.7 yr, calcite dissolution progressively decreased and was superceded by steady state dissolution of silicates, principally biotite. Mass balance calculations indicate that most calcite had been removed during this time and accounted for 57-98% of the total Ca released from these rocks. Experimental effluents from surfically weathered granitoids from the same watersheds were consistently dominated by silicate dissolution. The lack of excess Ca and alkalinity indicated that calcite had been previously removed by natural weathering. The extent of Ca enrichment in watershed discharge fluxes corresponds to the amounts of calcite exposed in granitoid rocks. High Ca/Na ratios relative to plagioclase stoichiometries indicate excess Ca in the Yosemite, Loch Vale, and other alpine watersheds in the Sierra Nevada and Rocky Mountains of the western United States. This Ca enrichment correlates with strong preferential weathering of calcite relative to plagioclase in exfoliated granitoids in glaciated terrains. In contrast, Ca/Na flux ratios are comparable to or less than the Ca/Na ratios for plagioclase in the subtropical Panola and tropical Rio Icacos watersheds, in which deeply weathered regoliths exhibit concurrent losses of calcite and much larger masses of plagioclase during transport-limited weathering. These results indicate that the weathering of accessory calcite may strongly influence Ca and alkalinity fluxes from silicate rocks during and following periods of glaciation and tectonism but is much less important for older stable geomorphic surfaces.

  1. Strain localization and the onset of dynamic weakening in calcite fault gouge

    NASA Astrophysics Data System (ADS)

    Smith, S. A. F.; Nielsen, S.; Di Toro, G.

    2015-03-01

    To determine the role of strain localization during dynamic weakening of calcite gouge at seismic slip rates, single-slide and slide-hold-slide experiments were conducted on 2-3-mm thick layers of calcite gouge at normal stresses up to 26 MPa and slip rates up to 1 m s-1. Microstructures were analyzed from short displacement (< 35 cm) experiments stopped prior to and during the transition to dynamic weakening. In fresh calcite gouge layers, dynamic weakening occurs after a prolonged strengthening phase that becomes shorter with increasing normal stress and decreasing layer thickness. Strain is initially distributed across the full thickness of the gouge layer, but within a few millimeters displacement the strain becomes localized to a boundary-parallel, high-strain shear band c. 20 ?m wide. During the strengthening phase, which lasts between 3 and 30 cm under the investigated conditions, the shear band broadens to become c. 100 ?m wide at peak stress. The transition to dynamic weakening in calcite gouges is associated with the nucleation of micro-slip surfaces dispersed throughout the c. 100 ?m wide shear band. Each slip surface is surrounded by aggregates of extremely fine grained and tightly packed calcite, interpreted to result from grain welding driven by local frictional heating in the shear band. By the end of dynamic weakening strain is localized to a single 2- 3-?m wide principal slip surface, flanked by layers of recrystallized gouge. Calcite gouge layers re-sheared following a hold period weaken nearly instantaneously, much like solid cylinders of calcite marble deformed under the same experimental conditions. This is due to reactivation of the recrystallized and cohesive principal slip surface that formed during the first slide, reducing the effective gouge layer thickness to a few microns. Our results suggest that formation of a high-strain shear band is a critical precursor to dynamic weakening in calcite gouges. Microstructures are most compatible with dynamic weakening resulting from a thermally triggered mechanism such as flash heating that requires both a high degree of strain localization and a minimum slip velocity to activate. The delayed onset of dynamic weakening in fresh calcite gouge layers, particularly at low normal stresses, may inhibit large coseismic slip at shallow crustal levels in calcite-bearing fault zones.

  2. Thermal and Evolved Gas Behavior of Calcite Under Mars Phoenix TEGA Operating Conditions

    NASA Technical Reports Server (NTRS)

    Ming, D.W.; Niles, P.B.; Morris, R.V.; Boynton, W.V.; Golden, D.C.; Lauer, H.V.; Sutter, B.

    2009-01-01

    The Mars Phoenix Scout Mission with its diverse instrument suite successfully examined several soils on the Northern plains of Mars. The Thermal and Evolved Gas Analyzer (TEGA) was employed to detect organic and inorganic materials by coupling a differential scanning calorimeter (DSC) with a magnetic-sector mass spectrometer (MS). Martian soil was heated up to 1000 C in the DSC ovens and evolved gases from mineral decomposition products were examined with the MS. TEGA s DSC has the capability to detect endothermic and exothermic reactions during heating that are characteristic of minerals present in the Martian soil. Initial TEGA results indicated the presence of endothermic peaks with onset temperatures that ranged from 675 C to 750 C with corresponding CO2 release. This result suggests the presence of calcite (CaCO3. CaO + CO2). Organic combustion to CO2 is not likely since this mostly occurs at temperatures below 550 C. Fe-carbonate and Mg-carbonate are not likely because their decomposition temperatures are less than 600 C. TEGA enthalpy determinations suggest that calcite, may occur in the Martian soil in concentrations of approx.1 to 5 wt. %. The detection of calcite could be questioned based on previous results that suggest Mars soils are mostly acidic. However, the Phoenix landing site soil pH was measured at pH 8.3 0.5, which is typical of terrestrial soils where pH is controlled by calcite solubility. The range of onset temperatures and calcite concentration as calculated by TEGA is poorly con-strained in part because of limited thermal data of cal-cite at reduced pressures. TEGA operates at <30 mbar while most calcite literature thermal data was obtained at 1000 mbar or higher pressures.

  3. Seasonal variations in modern speleothem calcite growth in Central Texas, U.S.A

    USGS Publications Warehouse

    Banner, J.L.; Guilfoyle, A.; James, E.W.; Stern, L.A.; Musgrove, M.

    2007-01-01

    Variations in growth rates of speleothem calcite have been hypothesized to reflect changes in a range of paleoenvironmental variables, including atmospheric temperature and precipitation, drip-water composition, and the rate of soil CO2 delivery to the subsurface. To test these hypotheses, we quantified growth rates of modern speleothem calcite on artificial substrates and monitored concurrent environmental conditions in three caves across the Edwards Plateau in central Texas. Within each of two caves, different drip sites exhibit similar annual cycles in calcite growth rates, even though there are large differences between the mean growth rates at the sites. The growth-rate cycles inversely correlate to seasonal changes in regional air temperature outside the caves, with near-zero growth rates during the warmest summer months, and peak growth rates in fall through spring. Drip sites from caves 130 km apart exhibit similar temporal patterns in calcite growth rate, indicating a controlling mechanism on at least this distance. The seasonal variations in calcite growth rate can be accounted for by a primary control by regional temperature effects on ventilation of cave-air CO2 concentrations and/or drip-water CO2 contents. In contrast, site-to-site differences in the magnitude of calcite growth rates within an individual cave appear to be controlled principally by differences in drip rate. A secondary control by drip rate on the growth rate temporal variations is suggested by interannual variations. No calcite growth was observed in the third cave, which has relatively high values of and small seasonal changes in cave-air CO2. These results indicate that growth-rate variations in ancient speleothems may serve as a paleoenvironmental proxy with seasonal resolution. By applying this approach of monitoring the modern system, speleothem growth rate and geochemical proxies for paleoenviromnental change may be evaluated and calibrated. Copyright ?? 2007, SEPM (Society for Sedimentary Geology).

  4. Probing the record of seawater carbonate chemistry in coccolithophore calcite

    NASA Astrophysics Data System (ADS)

    Candelier, Yael; Minoletti, Fabrice; Hermoso, Michael

    2013-04-01

    Previous works on the biogeochemistry of the ubiquist coccolithophore Calcidiscus leptoporus quantified an oxygen isotope fractionation of about -2.2 ‰ with respect to equilibrium. New cultures experiments and core top study of this taxon enable the calibration of the temperature dependance recorded in ?18O of this coccolith providing a new tool to decipher surfaces water temperatures through the Cenozoic. These findings, concordant in the two approaches show a reduced range of vital effect (-1.1 ‰ ). Other cultured and isolated species (Gephyrocapsa oceanica, Emiliania huxleyi and C.pelagicus) show similar patterns that raise the question of a possible overestimation of isotopic disequilibria in coccolith calcite. A promising research topic in palaeoceanography consists of exploiting interspecific isotopic fractionation because species respond differently to ambient changes in carbonate system chemistry. While E.huxleyi or G.oceanica are isotopically sensitive to changes in dissolved inorganic carbon speciation or concentration, others such as C.leptoporus remains almost unaffected. This may indicate that in addition to traditional ?18O temperature proxy, coccolith interspecific isotopic offsets can provide an innovative means to constrain the carbonate chemistry of the mixed-layer. We investigated this hypothesis with a study case of the last Pleistocene deglaciation that appears to be a good candidate by his abrupt changes in temperatures, oxygen isotope composition of seawater and atmospheric pCO2. While numerous studies have investigated climate changes at high latitudes, we present here the first coccoliths-based isotopic record of mixed-layer temperature at the border of North Atlantic Subtropical Gyre (southwards of the polar front). From Site DSDP 607 we successfully isolated fractions of coccolithophore species C.leptoporus, G.oceanica, E. huxleyi and C.pelagicus over the last 17 kyr. Oxygen isotope variations from these fractions exhibit a shift of about -1.9 ‰ between the Younger Dryas and the Early Holocene SSTs that can be translated into a warming of about 7-8 °C. This result closely matches with previously reported temperatures derived from foraminiferal and alkenone records and confirms that coccoliths can be used as a complementary or alternative substrate to foraminiferal shells for isotopic analyses and paleoclimate reconstructions. Differential oxygen and carbon isotopic offsets between Calcidiscus spp. and small Noelaerhabdacea coccoliths are almost constant and present an overall agreement with culture predictions. Although further results are needed this may imply that an increase of about 80 ppm pCO2 as recorded in Antarctica ice sheet over this time period is not sufficient to effect variations in calcification and intensity of fractionation in these two common species.

  5. 7 CFR 201.18 - Other agricultural seeds (crop seeds).

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 7 Agriculture 3 2011-01-01 2011-01-01 false Other agricultural seeds (crop seeds). 201.18 Section... SERVICE (Standards, Inspections, Marketing Practices), DEPARTMENT OF AGRICULTURE (CONTINUED) FEDERAL SEED ACT FEDERAL SEED ACT REGULATIONS Labeling Agricultural Seeds § 201.18 Other agricultural seeds...

  6. 7 CFR 201.18 - Other agricultural seeds (crop seeds).

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 7 Agriculture 3 2013-01-01 2013-01-01 false Other agricultural seeds (crop seeds). 201.18 Section... SERVICE (Standards, Inspections, Marketing Practices), DEPARTMENT OF AGRICULTURE (CONTINUED) FEDERAL SEED ACT FEDERAL SEED ACT REGULATIONS Labeling Agricultural Seeds § 201.18 Other agricultural seeds...

  7. 7 CFR 201.18 - Other agricultural seeds (crop seeds).

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 7 Agriculture 3 2014-01-01 2014-01-01 false Other agricultural seeds (crop seeds). 201.18 Section... SERVICE (Standards, Inspections, Marketing Practices), DEPARTMENT OF AGRICULTURE (CONTINUED) FEDERAL SEED ACT FEDERAL SEED ACT REGULATIONS Labeling Agricultural Seeds § 201.18 Other agricultural seeds...

  8. 7 CFR 201.18 - Other agricultural seeds (crop seeds).

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 7 Agriculture 3 2012-01-01 2012-01-01 false Other agricultural seeds (crop seeds). 201.18 Section... SERVICE (Standards, Inspections, Marketing Practices), DEPARTMENT OF AGRICULTURE (CONTINUED) FEDERAL SEED ACT FEDERAL SEED ACT REGULATIONS Labeling Agricultural Seeds § 201.18 Other agricultural seeds...

  9. 7 CFR 201.18 - Other agricultural seeds (crop seeds).

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 7 Agriculture 3 2010-01-01 2010-01-01 false Other agricultural seeds (crop seeds). 201.18 Section... SERVICE (Standards, Inspections, Marketing Practices), DEPARTMENT OF AGRICULTURE (CONTINUED) FEDERAL SEED ACT FEDERAL SEED ACT REGULATIONS Labeling Agricultural Seeds § 201.18 Other agricultural seeds...

  10. Crystallization of undercooled liquid fenofibrate.

    PubMed

    Amstad, Esther; Spaepen, Frans; Weitz, David A

    2015-11-28

    Formulation of hydrophobic drugs as amorphous materials is highly advantageous as this increases their solubility in water and therefore their bioavailability. However, many drugs have a high propensity to crystallize during production and storage, limiting the usefulness of amorphous drugs. We study the crystallization of undercooled liquid fenofibrate, a model hydrophobic drug. Nucleation is the rate-limiting step; once seeded with a fenofibrate crystal, the crystal rapidly grows by consuming the undercooled liquid fenofibrate. Crystal growth is limited by the incorporation of molecules into its surface. As nucleation and growth both entail incorporation of molecules into the surface, this process likely also limits the formation of nuclei and thus the crystallization of undercooled liquid fenofibrate, contributing to the good stability of undercooled liquid fenofibrate against crystallization. PMID:26506141

  11. Evaluating Cotton Seed Quality 

    E-print Network

    Boman, Randy

    2005-10-05

    , treated and bagged for planting the following season. Producers who plan to save seed from conventional varieties are advised to evaluatr seed quality before the planting season, using procedures such as the free fatty acid test, germination tests...

  12. Grape Seed Extract

    MedlinePLUS

    ... Extract Common Name: grape seed extract Latin Name: Vitis vinifera grapes.jpg © Steven Foster On this page: What ... naturaldatabase.com on June 25, 2009. Grape seed ( Vitis vinifera, Vitis coignetiae ). Natural Standard Database Web site. Accessed ...

  13. Method of making single crystal fibers

    NASA Technical Reports Server (NTRS)

    Westfall, Leonard J. (inventor)

    1990-01-01

    Single crystal fibers are made from miniature extruded ceramic feed rods. A decomposable binder is mixed with powders to inform a slurry which is extruded into a small rod which may be sintered, either in air or in vacuum, or it may be used in the extruded and dried condition. A pair of laser beams focuses onto the tip of the rod to melt it thereby forming a liquid portion. A single crystal seed fiber of the same material as the feed rod contacts this liquid portion to establish a zone of liquid material between the feed rod and the single crystal seed fiber. The feed rod and the single crystal feed fiber are moved at a predetermined speed to solidify the molten zone onto the seed fiber while simultaneously melting additional feed rod. In this manner a single crystal fiber is formed from the liquid portion.

  14. Vorticity analysis in calcite tectonites: An example from the Attico-Cycladic massif (Attica, Greece)

    NASA Astrophysics Data System (ADS)

    Spanos, D.; Xypolias, P.; Koukouvelas, I.

    2015-11-01

    Although calcite tectonites are widespread in nature their use to quantify flow vorticity is limited. We use new (micro-)structural, petrofabric and vorticity data to analyse the kinematics of flow in outcrop-scale calcite mylonite zones. These zones are genetically related to a crustal-scale NE-directed ductile thrust (Basal Thrust) that emplaced the Blueschist over the Basal unit during the exhumation of the Attico-Cycladic Massif. Calcite microstructures reveal that the last stage of deformation occurred at temperatures 200-300 °C achieved by mild heating, which is possibly related with the reburial of the Basal Thrust's footwall. Vorticity analyses were based on the degree of asymmetry of calcite c-axis fabrics as well as on the assumption that the orientation of the long axes of calcite neoblasts within an oblique foliation delineates the direction of instantaneous stretching axis. Both methodological approaches provide consistent estimates with a simple shear component between 55% and 82% (Wn = 0.76-0.96). The use of the stress axis (?1) orientation recorded by twin-c-axis-pairs to quantify vorticity generally gives significantly lower simple shear component. Comparison of our vorticity estimates with previous estimates inferred from quartz fabrics and rigid porphyroclasts reveals that exhumation-related deformation in the nappe pile was steady state.

  15. Dolomite-magnesian calcite relations at elevated temperatures and CO2 pressures

    USGS Publications Warehouse

    Graf, D.L.; Goldsmith, J.R.

    1955-01-01

    The equilibrium thermal decomposition curve of dolomite has been determined up to a CO2 pressure of 20,000 lb/in.2, at which pressure dolomite decomposes at 857??C. Equilibrium was approached from both directions, by the breakdown and by the solid-state synthesis of dolomite. At elevated temperatures and pressures, calcites in equilibrium with periclase as well as those in equilibrium with dolomite contain Mg in solid solution. In the former, the Mg content increases with increasing CO2 pressure, and decreases with increasing temperature. In the latter, it is a function of temperature only. The exsolution curve of dolomite and magnesian calcite has been determined between 500?? and 800??C; at 500?? dolomite is in equilibrium with a magnesian calcite containing ~6 mol per cent MgCO2; at 800??, ~22 mol per cent. There appears to be a small but real deviation from the ideal 1 : 1 Ca : Mg ratio of dolomite, in the direction of excess Ca, for material in equilibrium with magnesian calcite at high temperature. The experimental findings indicate that very little Mg is stable in the calcites of sedimentary environments, but that an appreciable amount is stable under higher-temperature metamorphic conditions, if sufficient CO2 pressure is maintained. ?? 1955.

  16. Influence of calcite on uranium(VI) reactive transport in the groundwater-river mixing zone.

    PubMed

    Ma, Rui; Liu, Chongxuan; Greskowiak, Janek; Prommer, Henning; Zachara, John; Zheng, Chunmiao

    2014-01-01

    Calcite is an important, relatively soluble mineral phase that can affect uranium reactive transport in subsurface sediments. This study was conducted to investigate the distribution of calcite and its influence on uranium adsorption and reactive transport in the groundwater-river mixing zone of the Hanford 300A site, Washington State. Simulations using a two-dimensional (2D) reactive transport model under field-relevant hydrological and hydrogeochemical conditions revealed the development of a calcite reaction front through the mixing zone as a result of dynamic groundwater-river interactions. The calcite concentration distribution, in turn, affected the concentrations of aqueous carbonate and calcium, and pH through dissolution, as river waters intruded and receded from the site at different velocities in response to stage changes. The composition variations in groundwater subsequently influenced uranium mobility and discharge rates into the river in a complex fashion. The results implied that calcite distribution and concentration are important variables that need to be quantified for accurate reactive transport predictions of uranium, especially in dynamic groundwater-river mixing zones. PMID:24240103

  17. Influence of calcite on uranium(VI) reactive transport in the groundwate-river mixing zone

    NASA Astrophysics Data System (ADS)

    Ma, Rui; Liu, Chongxuan; Greskowiak, Janek; Prommer, Henning; Zachara, John; Zheng, Chunmiao

    2014-01-01

    Calcite is an important, relatively soluble mineral phase that can affect uranium reactive transport in subsurface sediments. This study was conducted to investigate the distribution of calcite and its influence on uranium adsorption and reactive transport in the groundwate-river mixing zone of the Hanford 300A site, Washington State. Simulations using a two-dimensional (2D) reactive transport model under field-relevant hydrological and hydrogeochemical conditions revealed the development of a calcite reaction front through the mixing zone as a result of dynamic groundwate-river interactions. The calcite concentration distribution, in turn, affected the concentrations of aqueous carbonate and calcium, and pH through dissolution, as river waters intruded and receded from the site at different velocities in response to stage changes. The composition variations in groundwater subsequently influenced uranium mobility and discharge rates into the river in a complex fashion. The results implied that calcite distribution and concentration are important variables that need to be quantified for accurate reactive transport predictions of uranium, especially in dynamic groundwate-river mixing zones.

  18. Modeling results of calcium-containing minerals precipitation in the alkaline hydrotherms of Baikal Rift Zone: calcite and dolomite

    NASA Astrophysics Data System (ADS)

    Tokarenko, O. G.; Zippa, E. V.

    2015-11-01

    The calculation modeling results of the nitric hydrotherms saturation in Baikal Rift Zone with calcite and dolomite are presented. The calcite and dolomite make the carbonate barrier to thermal waters equilibrium with primary minerals of igneous rocks. In the research territory, there are three main types of geochemical thermal waters which are characterized by the saturation degree with the calcite and dolomite and the proportion of precipitating minerals phases. It has been established that nitric thermal waters-rock system has equilibrium with these minerals, which leads to bonding migrated from the rocks calcium and magnesium by the secondary formed minerals - calcite and dolomite.

  19. Infrared spectroscopy and density functional theory investigation of calcite, chalk, and coccoliths--do we observe the mineral surface?

    PubMed

    Andersson, M P; Hem, C P; Schultz, L N; Nielsen, J W; Pedersen, C S; Sand, K K; Okhrimenko, D V; Johnsson, A; Stipp, S L S

    2014-11-13

    We have measured infrared spectra from several types of calcite: chalk, freshly cultured coccoliths produced by three species of algae, natural calcite (Iceland Spar), and two types of synthetic calcite. The most intense infrared band, the asymmetric carbonate stretch vibration, is clearly asymmetric for the coccoliths and the synthetic calcite prepared using the carbonation method. It can be very well fitted by two peaks: a narrow Lorenzian at lower frequency and a broader Gaussian at higher frequency. These two samples both have a high specific surface area. Density functional theory for bulk calcite and several calcite surface systems allows for assignment of the infrared bands. The two peaks that make up the asymmetric carbonate stretch band come from the bulk (narrow Lorenzian) and from a combination of two effects (broad Gaussian): the surface or near surface of calcite and line broadening from macroscopic dielectric effects. We detect water adsorbed on the high surface area synthetic calcite, which permits observation of the chemistry of thin liquid films on calcite using transmission infrared spectroscopy. The combination of infrared spectroscopy and density functional theory also allowed us to quantify the amount of polysaccharides associated with the coccoliths. The amount of polysaccharides left in chalk, demonstrated to be present in other work, is below the IR detection limit, which is 0.5% by mass. PMID:25318063

  20. SEED DORMANCY, GENETICS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Technical Seed dormancy is defined as the temporary failure of a viable seed to germinate, after a specific length of time, in a particular set of environmental conditions that later evoke germination when the restrictive state has been terminated by either natural or artifical conditions. Seed dor...

  1. Needs of Seeds

    ERIC Educational Resources Information Center

    Keeley, Page

    2011-01-01

    The "Needs of Seeds" formative assessment probe can be used to find out whether students recognize that seeds have needs both similar to and different from plants and other living organisms (Keeley, Eberle, and Tugel 2007). The probe reveals whether students overgeneralize the needs of seeds by assuming they have the same needs as the adult plants…

  2. Preservation of recalcitrant seeds

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Recalcitrant and intermediate seeds are not included in seed banks because of misperceptions that these efforts would be futile. Between 20 and 25% of the Earth’s angiosperm species are estimated to produce recalcitrant or intermediate seeds. These species are more prevalent in the tropics and sub...

  3. Seed Development and Germination

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Seed is the fertilized and matured ovule of angiosperms and gymnosperms and represents a crucial stage in the life cycle of plants. Seeds of diverse plant species may display differences in size, shape and color. Despite apparent morphological variations, most mature seeds consist of three major com...

  4. Seeds as allelopathic agents.

    PubMed

    Friedman, J; Waller, G R

    1983-08-01

    Inhibitors of germination or of growth, highly diversified chemicals are commonly found in higher plants. They occur in vegetative organs as well as in seeds or other dispersal units. Nonprotein amino acids, when present, are mainly found in seeds where they can occur in extremely high concentrations. Density of seeds, rate of emanation of inhibitors, their amount and effectiveness, all determine allelopathic potential of seeds. To induce allelopathy, rate of emanation of inhibitors must be fast and of sufficient duration. Our observations in coffee seedsCoffea arabica L. indicate that rate of emanation of the inhibitor caffeine is highly enhanced during senescence of seeds, suggesting that when allelopathic potential of seeds is evaluated the presence of both young and old seeds should be considered. In many plants seeds are liberated close to the parent plant, the zone where seed-induced allelopathy may occur. Large numbers of seeds are usually produced in order to ensure establishment; greater number and mass of seeds may also increase allelopathic inhibition of competing vegetation. PMID:24407804

  5. Quartz crystal growth

    SciTech Connect

    Baughman, R.J.

    1992-08-04

    This patent describes a process for growing high quality single crystals of a nutrient substance that can undergo phase transformation from the amorphous to the crystalline state in an appropriate solvent, charging the substance, seed crystals of the substance, and the solvent in an autoclave having a lower dissolution zone connecting with an upper crystallization zone; allowing the close charged autoclave to stand at ambient temperature for a time sufficient to reach internal equilibrium; gradually heating the autoclave at a rate such that a very small temperature differential ([Delta]T) is maintained between the cooler upper zone and the warmer lower zone until the nutrient substance has undergone transformation to the crystalline phase; and increasing the heating rate to achieve and maintain a larger temperature differential ([Delta]T) between the zones sufficient to allow increased material transport between the zones and rapid controlled crystal growth.

  6. Evaluation of Sierra Nevada seeding effects on snowfall processes and distribution. Final report, 1 July 1988-30 June 1989

    SciTech Connect

    Warburton, J.A.

    1990-10-01

    Studies were conducted in regions of the central Sierra Nevada to determine the distribution of seeding aerosols in seeded target areas. These studies involved field operations of seeding and snow sampling equipment and cloud chamber investigations of ice crystal morphology. Secondary ice formation and chemical reactions including aerosol removal processes.

  7. Growth of bulk GaN crystal by Na flux method under various conditions

    NASA Astrophysics Data System (ADS)

    Mori, Y.; Imade, M.; Murakami, K.; Takazawa, H.; Imabayashi, H.; Todoroki, Y.; Kitamoto, K.; Maruyama, M.; Yoshimura, M.; Kitaoka, Y.; Sasaki, T.

    2012-07-01

    High-quality and low cost bulk crystals are needed in the field of group III nitride semiconductors in order to develop optical and electrical devices. There are two approaches for the growth of bulk GaN crystal by the Na flux method. One is to grow thick GaN crystal on a large seed GaN crystal grown by vapor phase method. The other is to grow GaN crystal on a small seed GaN crystal. 3 in diameter GaN crystals were grown on the large GaN seed crystal. In the case of the growth on a small GaN seed, we obtained bulk crystal with a pyramidal shape and its height and diameter were 15 mm and >20 mm, respectively. We also present the effects of the impurity in the solution on the property and growth habit.

  8. Crystal growth in fused solvent systems. [in space environment

    NASA Technical Reports Server (NTRS)

    Ulrich, D. R.; Noval, B. A.; White, W. B.; Spear, K. E.; Henry, E. C.

    1974-01-01

    The successful nucleation of bismuth germanate, B12GeO20 on a high quality seed and the growth of regions of single crystals of the same orientation of the seed are reported. Lead germanate, Pb5Ge3O11 was also identified as a ferroelectric crystal with large electrooptic and nonlinear optic constants. Solvent criteria, solvent/development, and crystal growth are discussed, and recommendations for future studies are included.

  9. Structure of the (1014) Surfaces of Calcite, Dolomite, and Magnesite under Wet and Dry Conditions

    SciTech Connect

    WRIGHT,KATE; CYGAN,RANDALL T.; SLATER,BEN

    2000-06-12

    Atomistic computer simulation methods have been employed to model the structure of the (10{bar 1}4) surfaces of calcite, dolomite and magnesite. The authors calculations show that under vacuum conditions, calcite undergoes the greatest degree of surface relaxation with rotation and distortion of the carbonate group accompanied by movement of the calcium ion. The magnesite surface is the least distorted of the three carbonates, with dolomite being intermediate to the two end members. When water molecules are placed on the surface to produce complete monolayer coverage, the calcite surface is stabilized and the amount of relaxation is substantially reduced. In contrast, the dolomite and magnesite surfaces are destabilized by hydration as indicated by a significant increase in the surface energies relative to the dry surface.

  10. Strontium isotope evolution of pore water and calcite in the Topopah Spring Tuff, Yucca Mountain, Nevada

    SciTech Connect

    Marshall, Brian D.; Futa, Kiyoto

    2001-04-29

    Pore water in the Topopah Spring Tuff has a narrow range of {delta}{sup 87}Sr values that can be calculated from the {delta}{sup 87}Sr values of the rock considering advection through and reaction with the overlying nonwelded tuffs of the PTn. This model can be extended to estimate the variation of {delta}{sup 87}Sr in the pore water through time; this approximates the variation of {delta}{sup 87}Sr measured in calcite fracture coatings. In samples of calcite where no silica can be dated by other methods, strontium isotope data may be the only method to determine ages. In addition, other Sr-bearing minerals in the calcite and opal coatings, such as fluorite, may be dated using the same model.

  11. Static Grain Growth in Contact Metamorphic Calcite: A Cathodoluminescence Study.

    NASA Astrophysics Data System (ADS)

    Vogt, B.; Heilbronner, R.; Herwegh, M.; Ramseyer, K.

    2009-04-01

    In the Adamello contact aureole, monomineralic mesozoic limestones were investigated in terms of grain size evolution and compared to results on numerical modeling performed by Elle. The sampled area shows no deformation and therefore represents an appropriate natural laboratory for the study of static grain growth (Herwegh & Berger, 2003). For this purpose, samples were collected at different distances to the contact to the pluton, covering a temperature range between 270 to 630°C. In these marbles, the grain sizes increase with temperature from 5 µm to about 1 cm as one approaches the contact (Herwegh & Berger, 2003). In some samples, photomicrographs show domains of variable cathodoluminescence (CL) intensities, which are interpreted to represent growth zonations. Microstructures show grains that contain cores and in some samples even several growth stages. The cores are usually not centered and the zones not concentric. They may be in touch with grain boundaries. These zonation patterns are consistent within a given aggregate but differ among the samples even if they come from the same location. Relative CL intensities depend on the Mn/Fe ratio. We assume that changes in trace amounts of Mn/Fe must have occurred during the grain size evolution, preserving local geochemical trends and their variations with time. Changes in Mn/Fe ratios can either be explained by (a) locally derived fluids (e.g. hydration reactions of sheet silicate rich marbles in the vicinity) or (b) by the infiltration of the calcite aggregates by externally derived (magmatic?) fluids. At the present stage, we prefer a regional change in fluid composition (b) because the growth zonations only occur at distances of 750-1250 m from the pluton contact (350-450°C). Closer to the contact, neither zonations nor cores were found. At larger distances, CL intensities differ from grain to grain, revealing diagenetic CL patterns that were incompletely recrystallized by grain growth. The role of infiltration of magmatic fluids is also manifest in the vicinity of dikes, where intense zonation patterns are prominent in the marbles. The software Elle was developed to simulate microstructural evolution in rocks. The numerical model with the title "Grain boundary sweeping" was performed by M. Jessell and was found on http://www.materialsknowledge.org/elle. It displays the grain size evolution and the development of growth zonations during grain boundary migration of a 2D foam structure. This simulation was chosen because the driving force is the minimization of isotropic surface energies. It will be compared to the natural microstructures. At the last stage of the simulation the average grain and core sizes have increased. All, even the smallest grains, show growth zonations. Grains can be divided into two groups: (a) initially larger grains, increasing their grain size and maintaining their core size and (b) initially smaller grains with decreasing grain and decreasing core size. Group (a) grains show large areas swept by grain boundaries into the direction of small grains. Grain boundaries between large grains move more slowly. Their cores do not touch any grain boundaries. Cores of group (b) grains are in contact with the grain boundary network and are on the way to be consumed. In the numerical model and in the natural example similar features can be observed: The cores are not necessarily centered, the zonations are not necessarily concentric and some of the cores touch the grain boundary network. In the simulation, grain boundary migration velocity between large grains is smaller than between a large and a small grain. From this we would predict that - given enough time - a well sorted grain size distribution of increased grain size could be generated. But since many small grains occur we infer that this equilibrium has not been obtained. Analytical results of some natural samples that could be analyzed up to now indicate a relatively well sorted grain size distribution suggesting a more mature state of static grain growth. In comparison t

  12. Seeding date and polymer seed coating effects on plant establishment and yield of fall-seeded

    E-print Network

    Lawrence, Rick L.

    Seeding date and polymer seed coating effects on plant establishment and yield of fall-seeded. and Kirkland, K. J. 2004. Seeding date and polymer seed coating effects on plant establishment and yield of fall-seeded canola in the Northern Great Plains. Can. J. Plant Sci. 84: 955­963. The time interval

  13. Hydrothermal Growth of Polyscale Crystals

    NASA Astrophysics Data System (ADS)

    Byrappa, Kullaiah

    In this chapter, the importance of the hydrothermal technique for growth of polyscale crystals is discussed with reference to its efficiency in synthesizing high-quality crystals of various sizes for modern technological applications. The historical development of the hydrothermal technique is briefly discussed, to show its evolution over time. Also some of the important types of apparatus used in routine hydrothermal research, including the continuous production of nanosize crystals, are discussed. The latest trends in the hydrothermal growth of crystals, such as thermodynamic modeling and understanding of the solution chemistry, are elucidated with appropriate examples. The growth of some selected bulk, fine, and nanosized crystals of current technological significance, such as quartz, aluminum and gallium berlinites, calcite, gemstones, rare-earth vanadates, electroceramic titanates, and carbon polymorphs, is discussed in detail. Future trends in the hydrothermal technique, required to meet the challenges of fast-growing demand for materials in various technological fields, are described. At the end of this chapter, an Appendix 18.A containing a more or less complete list of the characteristic families of crystals synthesized by the hydrothermal technique is given with the solvent and pressure-temperature (PT) conditions used in their synthesis.

  14. Burial Diagenesis Effects on Clumped Isotope Signatures of Coexisting Dolomites and Calcites

    NASA Astrophysics Data System (ADS)

    Winkelstern, I. Z.; Lohmann, K. C.

    2014-12-01

    Carbonate clumped isotope paleothermometry is a promising method for diagenetic and deep time paleoclimate studies, but original clumped isotope (?47) compositions can be altered by fluid and thermal diagenetic processes. Previous work shows ?47 resetting of calcite occurs at temperatures exceeding 100°C over time periods of millions of years, but such thermally-driven effects have not been considered for dolomite. Differences between calcite and dolomite temperature calibrations are also largely unquantified, and the effect of burial diagenesis on dolomite ?47 has not been measured. Coexisting calcites and dolomites in a ~4500 meter core from Andros Island, Bahamas, offer a unique opportunity to address these questions. These dolomites and calcites formed over a time span from the Cretaceous to Pleistocene under near-surface temperature conditions. Clumped isotope analysis of this material reveals that where these carbonate phases are buried to depths greater than ~3000 meters, realistic surface temperatures (~25 °C) are not preserved. Moreover, these phases do not record reasonable geothermal conditions (> 80 °C), but rather record temperatures between 40 and 60°C. Here we evaluate whether this ?47 "error" is due to solid-state resetting of clumped isotopes, emplacement of minor burial cements, fabric retentive recrystallization, or some combination thereof. Our results show that clumped isotope compositions of both calcite and dolomite respond similarly to diagenetic resetting of primary values under conditions of burial. These data further emphasize the need to constrain the diagenetic history of samples used for clumped isotope work. The similar ?47 temperatures recorded by each carbonate type suggest that dolomites and calcites are equally viable temperature proxy sources under shallow burial conditions, yet both seem equally susceptible to "resetting" of their primary clumped isotope abundances.

  15. Interpretation of speleothem calcite ?13C variations: Evidence from monitoring soil CO2, drip water, and modern speleothem calcite in central Texas

    NASA Astrophysics Data System (ADS)

    Meyer, Kyle W.; Feng, Weimin; Breecker, Daniel O.; Banner, Jay L.; Guilfoyle, Amber

    2014-10-01

    We studied the sources and transport of carbon in two active karst systems in central Texas, Inner Space Cavern (IS) and Natural Bridge North and South Caverns (NB), to provide new insights into the interpretation of speleothem (cave calcite deposit) carbon isotope compositions. We have determined the ?13C values of soil CO2 (?13Cs) in grassland and savanna above these caves with ?13C values of cave drip water (?13CHCO3-) and modern speleothem calcite grown on artificial substrates (?13Ccc). We compare ?13CHCO3- values from direct drip sites, where water was sampled immediately upon discharging from the cave ceiling, to values from indirect sites, where water was sampled after flowing along a prolonged path within the cave that allowed for longer CO2 degassing and have found that direct drip sites yield consistently lower ?13CHCO3- values. The ?13CHCO3- values of direct drip water below savanna (-10.6 ± 0.5‰ and -12.6 ± 0.2‰, in NB and IS, respectively) are indistinguishable from (IS) or similar to (NB) calculated ?13CHCO3- values in equilibrium with measured soil CO2 beneath trees (-13.5‰ to -11.3‰ for juniper trees above NB, and -13.6‰ to -12.6‰ for mixed oak and elm trees above IS, respectively). At IS, the ?13CHCO3- values of direct drip water are higher below grassland (-9.7 ± 0.3‰) than below savanna (12.6 ± 0.2‰). These results suggest that the ?13CHCO3- values of drip waters that initially enter the caves are controlled by deep-rooted plants, where present, and are minimally influenced by host-rock dissolution and/or prior calcite precipitation (PCP). The ?13CHCO3- values of indirect drip water vary seasonally with relatively low values during the summer (-10.8 ± 0.8‰ and -9.2 ± 0.4‰ under juniper savanna at NB and under grassland at IS, respectively) that are similar to the direct drip ?13CHCO3- values (-10.6 ± 0.5‰ and -9.7 ± 0.3‰ under savanna at NB and under grassland at IS, respectively). The relatively high ?13CHCO3- values of indirect drip sites during the winter (?13CHCO3- = -8.6 ± 0.8‰ at NB and 8.0 ± 0.1‰ at IS) result from CO2 degassing of water along in-cave flow paths. We also present decade-long records of modern calcite ?13C values from direct and indirect drip sites at IS. The ?13Ccc values vary seasonally with lower values during the summer and higher values during the winter, and with smaller amplitude variations at the direct drip site. Such seasonal variations can be used as a geochronological tool in some speleothems that do not contain visible lamina. The summer ?13Ccc values of direct drip calcite are similar to ?13Ccc values predicted from soil CO2 collected beneath trees above that drip site. The occurrence of highest ?13Ccc values during the winter, when cave CO2 concentrations are low, highlights the significance of ventilation-driven changes in cave-air pCO2. Modern calcite ?13C values are also negatively correlated with drip rate, which suggests that ?13Ccc variations are controlled by kinetic effects during degassing and calcite precipitation associated with the drip water exposure time to a low-pCO2 environment. In all, at the caves we investigated, variability in speleothem ?13Ccc values primarily reflect presence/absence of deep-rooted vegetation and kinetic isotope effects. We therefore infer that increased aridity may result in higher ?13C values of vegetation, lower drip rates and more drip water degassing, and thus higher ?13Ccc values of speleothem calcite.

  16. Galacturonomannan and Golgi-derived membrane linked to growth and shaping of biogenic calcite

    NASA Technical Reports Server (NTRS)

    Marsh, M. E.; Ridall, A. L.; Azadi, P.; Duke, P. J.

    2002-01-01

    The coccolithophores are valuable models for the design and synthesis of composite materials, because the cellular machinery controlling the nucleation, growth, and patterning of their calcitic scales (coccoliths) can be examined genetically. The coccoliths are formed within the Golgi complex and are the major CaCO(3) component in limestone sediments-particularly those of the Cretaceous period. In this study, we describe mutants lacking a sulfated galacturonomannan and show that this polysaccharide in conjunction with the Golgi-derived membrane is directly linked to the growth and shaping of coccolith calcite but not to the initial orientated nucleation of the mineral phase.

  17. U and Sr Isotopes in ground water and calcite, Yucca Mountain, Nevada: Evidence against upwelling water

    USGS Publications Warehouse

    Stuckless, J.S.; Peterman, Z.E.; Muhs, D.R.

    1991-01-01

    Hydrogenic calcite and opaline silica deposits in fault zones at Yucca Mountain, Nevada, have created considerable public and scientific controversy because of the possible development of a high-level nuclear waste repository at this location. Strontium and uranium isotopic compositions of hydrogenic materials were used to test whether the veins could have formed by upwelling of deep-seated waters. The vein deposits are isotopically distinct from ground water in the two aquifers that underlie Yucca Mountain, indicating that the calcite could not have precipitated from ground water. The data are consistent with a surficial origin for the hydrogenic deposits.

  18. Britholite, monazite, REE carbonates, and calcite: Products of hydrothermal alteration of allanite and apatite in A-type granite from Stupné, Western Carpathians, Slovakia

    NASA Astrophysics Data System (ADS)

    Uher, Pavel; Ondrejka, Martin; Ba?ík, Peter; Broska, Igor; Kone?ný, Patrik

    2015-11-01

    An uncommon assemblage of primary and secondary accessory REE minerals was identified in a Permian A-type granite clast in polymict conglomerates intercalated in the Cretaceous flysch sequence of the Pieniny Klippen Belt, Western Carpathians, northwest Slovakia. A detailed electron-microprobe study of the granite reveals extensive subsolidus alteration of primary magmatic allanite-(Ce) to ferriallanite-(Ce) and fluorapatite. The Y, Ce-rich fluorapatite was replaced by the dissolution-reprecipitation process to the britholite group mineral members: fluorbritholite-(Y), britholite-(Y), fluorcalciobritholite, and its hydroxyl-dominant analogue ("calciobritholite"). Britholite-(Y) contains up to 5.2 wt.% ThO2 (0.15 apfu Th); the highest Th content yet reported in naturally occurring Y-dominant britholites. Moreover, the alteration of (ferri)allanite-(Ce) resulted to complex pseudomorphs and overgrowths, including mainly REE carbonate phases: [synchysite-(Ce) to its hydroxyl-dominant analogue "hydroxylsynchysite-(Ce)", bastnäsite-(Ce)] and calcite, rarely monazite-(Ce), epidote, clinochlore, titanite, TiO2 phase, and pseudorutile. In some cases, secondary carbonate minerals (mainly synchysite and calcite) replaced a substantial part of former allanite crystals. Moreover, primary magmatic biotite (annite) was partly transformed to acicular stilpnomelane. Textural and compositional data indicate extensive replacement and breakdown of the primary magmatic allanite and apatite by aqueous fluids rich in fluorine and carbon, liberated during a younger post-magmatic, low-temperature hydrothermal-metamorphic overprint of the granite.

  19. Not all calcite ballast is created equal: differing effects of foraminiferan and coccolith calcite on the formation and sinking of aggregates

    NASA Astrophysics Data System (ADS)

    Schmidt, K.; De La Rocha, C. L.; Gallinari, M.; Cortese, G.

    2014-01-01

    Correlation between particulate organic carbon (POC) and calcium carbonate sinking through the deep ocean has led to the idea that ballast provided by calcium carbonate is important for the export of POC from the surface ocean. While this idea is certainly to some extent true, it is worth considering in more nuance, for example, examining the different effects on the aggregation and sinking of POC of small, non-sinking calcite particles like coccoliths and large, rapidly sinking calcite like planktonic foraminiferan tests. We have done that here in a simple experiment carried out in roller tanks that allow particles to sink continuously without being impeded by container walls. Coccoliths were efficiently incorporated into aggregates that formed during the experiment, increasing their sinking speed compared to similarly sized aggregates lacking added calcite ballast. The foraminiferan tests, which sank as fast as 700 m d-1, became associated with only very minor amounts of POC. In addition, when they collided with other, larger, foram-less aggregates, they fragmented them into two smaller, more slowly sinking aggregates. While these effects were certainly exaggerated within the confines of the rolling tanks, they clearly demonstrate that calcium carbonate ballast is not just calcium carbonate ballast - different forms of calcium carbonate ballast have notably different effects on POC aggregation, sinking, and export.

  20. Not all calcite ballast is created equal: differing effects of foraminiferan and coccolith calcite on the formation and sinking of aggregates

    NASA Astrophysics Data System (ADS)

    Schmidt, K.; De La Rocha, C. L.; Gallinari, M.; Cortese, G.

    2013-09-01

    Correlation between particulate organic carbon (POC) and calcium carbonate sinking through the deep ocean has led to the idea that ballast provided by calcium carbonate is important for the export of POC from the surface ocean. While this idea is certainly to some extent true, it is worth considering in more nuance, for example, examining the different effects on the aggregation and sinking of POC of small, non-sinking calcite particles like coccoliths and large, rapidly sinking calcite like planktonic foraminiferan tests. We have done that here in a simple experiment carried out in roller tanks that allow particles to sink continuously without being impeded by container walls. Coccoliths were efficiently incorporated into aggregates that formed during the experiment, increasing their sinking speed compared to similarly sized aggregates lacking added calcite ballast. The foraminiferan tests, which sank as fast as 700 m d-1, became associated with only very minor amounts of POC. In addition, when they collided with other, larger, foraminferan-less aggregates, they fragmented them into two smaller, more slowly sinking aggregates. While these effects were certainly exaggerated within the confines of the roller tanks, they clearly demonstrate that calcium carbonate ballast is not just calcium carbonate ballast- different forms of calcium carbonate ballast have notably different effects on POC aggregation, sinking, and export.

  1. Structure of struthiocalcin-1, an intramineral protein from Struthio camelus eggshell, in two crystal forms.

    PubMed

    Ruiz-Arellano, Rayana R; Medrano, Francisco J; Moreno, Abel; Romero, Antonio

    2015-04-01

    Biomineralization is the process by which living organisms produce minerals. One remarkable example is the formation of eggshells in birds. Struthiocalcins present in the ostrich (Struthio camellus) eggshell matrix act as biosensors of calcite growth during eggshell formation. Here, the crystal structure of struthiocalcin-1 (SCA-1) is reported in two different crystal forms. The structure is a compact single domain with an ?/? fold characteristic of the C-type lectin family. In contrast to the related avian ovocleidin OC17, the electrostatic potential on the molecular surface is dominated by an acidic patch. Scanning electron microscopy combined with Raman spectroscopy indicates that these intramineral proteins (SCA-1 and SCA-2) induce calcium carbonate precipitation, leading to the formation of a stable form of calcite in the mature eggshell. Finally, the implications of these two intramineral proteins SCA-1 and SCA-2 in the nucleation of calcite during the formation of eggshells in ratite birds are discussed. PMID:25849392

  2. Seeding cirrus clouds could drive global net cooling

    NASA Astrophysics Data System (ADS)

    Wendel, JoAnna

    2014-07-01

    Cirrus clouds—thin, wispy streamers that form in the upper troposphere when ice crystals nucleate around small dust or metallic particles—have a net warming effect on climate. Previous studies have suggested that seeding cirrus clouds with an overload of dust particles reduces their formation and lifespan, thus leading to a net cooling effect on global climate. Recently, however, research has raised questions regarding how exactly cirrus clouds form, which has implications for seeding strategies.

  3. Seed-Mediated Growth of Gold Nanocrystals: Changes to the Crystallinity or Morphology as Induced by the Treatment of Seeds with a Sulfur Species

    SciTech Connect

    Zheng, Yiqun; Luo, Ming; Tao, Jing; Peng, Hsin-Chieh; Wan, Dehui; Zhu, Yimei; Xia, Younan

    2014-12-11

    We report our observation of changes to the crystallinity or morphology during seed-mediated growth of Au nanocrystals. When single-crystal Au seeds with a spherical or rod-like shape were treated with a chemical species such as S?O?²? ions, twin defects were developed during the growth process to generate multiply twinned nanostructures. X-ray photoelectron spectroscopy analysis indicated that the S?O?²? ions were chemisorbed on the surfaces of the seeds during the treatment. The chemisorbed S?O?²? ions somehow influenced the crystallization of Au atoms added onto the surface during a growth process, leading to the formation of twin defects. In contrast to the spherical and rod-like Au seeds, the single-crystal structure was retained to generate a concave morphology when single-crystal Au seeds with a cubic or octahedral shape were used for a similar treatment and then seed-mediated growth. The different outcomes are likely related to the difference in spatial distribution of S?O?²? ions chemisorbed on the surface of a seed. This approach based on surface modification is potentially extendable to other noble metals for engineering the crystallinity and morphology of nanocrystals formed via seed-mediated growth.

  4. Seed-Mediated Growth of Gold Nanocrystals: Changes to the Crystallinity or Morphology as Induced by the Treatment of Seeds with a Sulfur Species

    DOE PAGESBeta

    Zheng, Yiqun; Luo, Ming; Tao, Jing; Peng, Hsin-Chieh; Wan, Dehui; Zhu, Yimei; Xia, Younan

    2014-12-11

    We report our observation of changes to the crystallinity or morphology during seed-mediated growth of Au nanocrystals. When single-crystal Au seeds with a spherical or rod-like shape were treated with a chemical species such as S?O?²? ions, twin defects were developed during the growth process to generate multiply twinned nanostructures. X-ray photoelectron spectroscopy analysis indicated that the S?O?²? ions were chemisorbed on the surfaces of the seeds during the treatment. The chemisorbed S?O?²? ions somehow influenced the crystallization of Au atoms added onto the surface during a growth process, leading to the formation of twin defects. In contrast to themore »spherical and rod-like Au seeds, the single-crystal structure was retained to generate a concave morphology when single-crystal Au seeds with a cubic or octahedral shape were used for a similar treatment and then seed-mediated growth. The different outcomes are likely related to the difference in spatial distribution of S?O?²? ions chemisorbed on the surface of a seed. This approach based on surface modification is potentially extendable to other noble metals for engineering the crystallinity and morphology of nanocrystals formed via seed-mediated growth.« less

  5. Seed-mediated growth of gold nanocrystals: changes to the crystallinity or morphology as induced by the treatment of seeds with a sulfur species.

    PubMed

    Zheng, Yiqun; Luo, Ming; Tao, Jing; Peng, Hsin-Chieh; Wan, Dehui; Zhu, Yimei; Xia, Younan

    2014-12-11

    We report our observation of changes to the crystallinity or morphology during seed-mediated growth of Au nanocrystals. When single-crystal Au seeds with a spherical or rod-like shape were treated with a chemical species such as S2O3(2-) ions, twin defects were developed during the growth process to generate multiply twinned nanostructures. X-ray photoelectron spectroscopy analysis indicated that the S2O3(2-) ions were chemisorbed on the surfaces of the seeds during the treatment. The chemisorbed S2O3(2-) ions somehow influenced the crystallization of Au atoms added onto the surface during a growth process, leading to the formation of twin defects. In contrast to the spherical and rod-like Au seeds, the single-crystal structure was retained to generate a concave morphology when single-crystal Au seeds with a cubic or octahedral shape were used for a similar treatment and then seed-mediated growth. The different outcomes are likely related to the difference in spatial distribution of S2O3(2-) ions chemisorbed on the surface of a seed. This approach based on surface modification is potentially extendable to other noble metals for engineering the crystallinity and morphology of nanocrystals formed via seed-mediated growth. PMID:25243840

  6. Controlled crystallization of emerald from the fluxed melt

    NASA Astrophysics Data System (ADS)

    Barilo, S. N.; Bychkov, G. L.; Kurnevich, L. A.; Leonuk, N. I.; Mikhailov, V. P.; Shiryaev, S. V.; Koyava, V. T.; Smirnova, T. V.

    1999-03-01

    The problem of controlled crystallization of emerald single crystals from a fluxed melt, its colour characteristics and optic parameters are discussed. Properties of the as-grown single crystals are very much like those of natural gems. Emeralds weighting as much as 150 ct grown on oriented seeds in dynamical regime feature small dichroism, uniform distribution of colour in the volume to offer good jewelry characteristics. The (1 0 1¯ 0) and (1 1 2¯ 0) cuts of previously grown crystals is established to be the optimal seed. The technique has the advantage of maintaining the optimal concentration ratio of the solute near the crystallization front through adequate stirring by a platinum crystal holder is rotated at a rate of 30 rounds per minute, and seed positioning. To examine emerald crystals quality we have performed a laser experiment and threshold measurements. Lasing was achieved at absorbed pump energy threshold of less than 0.6 mJ.

  7. Quartz crystal growth

    DOEpatents

    Baughman, Richard J. (Albuquerque, NM)

    1992-01-01

    A process for growing single crystals from an amorphous substance that can undergo phase transformation to the crystalline state in an appropriate solvent. The process is carried out in an autoclave having a lower dissolution zone and an upper crystallization zone between which a temperature differential (.DELTA.T) is maintained at all times. The apparatus loaded with the substance, solvent, and seed crystals is heated slowly maintaining a very low .DELTA.T between the warmer lower zone and cooler upper zone until the amorphous substance is transformed to the crystalline state in the lower zone. The heating rate is then increased to maintain a large .DELTA.T sufficient to increase material transport between the zones and rapid crystallization. .alpha.-Quartz single crystal can thus be made from fused quartz in caustic solvent by heating to 350.degree. C. stepwise with a .DELTA.T of 0.25.degree.-3.degree. C., increasing the .DELTA.T to about 50.degree. C. after the fused quartz has crystallized, and maintaining these conditions until crystal growth in the upper zone is completed.

  8. Chemistry of the calcite/water interface: Influence of sulfate ions and consequences in terms of cohesion forces

    SciTech Connect

    Pourchet, Sylvie Pochard, Isabelle; Brunel, Fabrice; Perrey, Danièle

    2013-10-15

    Calcite suspensions are used to mimic the behavior of more complex cementitious systems. Therefore the characterization of calcite–water interface in strong alkaline conditions, through ionic adsorption, electrokinetic measurements, static rheology and atomic force microscopy is a prerequisite. Calcium, a potential determining ion for calcite, adsorbs specifically onto the weakly positively charged calcite surface in water. This leads to an increase of the repulsive electric double layer force and thus weakens the particle cohesion. Sulfate adsorption, made at constant calcium concentration and ionic strength, significantly increases the attractive interactions between the calcite particles despite its very low adsorption. This is attributed to a lowering of the electrostatic repulsion in connection with the evolution of the zeta potential. The linear relationship found between the yield stress and ?{sup 2} proves that the classical DLVO theory applies for these systems, contrary to what was previously observed with C–S–H particles under the same conditions.

  9. Real-Time Control of a Semi-Industrial Fed-Batch Evaporative Crystallizer Using Different

    E-print Network

    Van den Hof, Paul

    Real-Time Control of a Semi-Industrial Fed- Batch Evaporative Crystallizer Using Different Direct approach for optimal operation of a seeded fed-batch evaporative crystallizer. Various direct optimization

  10. Probing the energetics of organic–nanoparticle interactions of ethanol on calcite

    PubMed Central

    Wu, Di; Navrotsky, Alexandra

    2015-01-01

    Knowing the nature of interactions between small organic molecules and surfaces of nanoparticles (NP) is crucial for fundamental understanding of natural phenomena and engineering processes. Herein, we report direct adsorption enthalpy measurement of ethanol on a series of calcite nanocrystals, with the aim of mimicking organic–NP interactions in various environments. The energetics suggests a spectrum of adsorption events as a function of coverage: strongest initial chemisorption on active sites on fresh calcite surfaces, followed by major chemical binding to form an ethanol monolayer and, subsequently, very weak, near-zero energy, physisorption. These thermochemical observations directly support a structure where the ethanol monolayer is bonded to the calcite surface through its polar hydroxyl group, leaving the hydrophobic ends of the ethanol molecules to interact only weakly with the next layer of adsorbing ethanol and resulting in a spatial gap with low ethanol density between the monolayer and subsequent added ethanol molecules, as predicted by molecular dynamics and density functional calculations. Such an ordered assembly of ethanol on calcite NP is analogous to, although less strongly bonded than, a capping layer of organics intentionally introduced during NP synthesis, and suggests a continuous variation of surface structure depending on molecular chemistry, ranging from largely disordered surface layers to ordered layers that nevertheless are mobile and can rearrange or be displaced by other molecules to strongly bonded immobile organic capping layers. These differences in surface structure will affect chemical reactions, including the further nucleation and growth of nanocrystals on organic ligand-capped surfaces. PMID:25870281

  11. STIMULATION OF MICROBIAL UREA HYDROLYSIS IN GROUNDWATER TO ENHANCE CALCITE PRECIPITATION

    SciTech Connect

    Yoshiko Fujita; Joanna L. Taylor; Tina L. Gresham; Mark E. Delwiche; Frederick S. Colwell; Travis McLing; Lynn Petzke; Robert W. Smith

    2008-04-01

    Sequential addition of molasses and urea was tested as a means of stimulating microbial urea hydrolysis in the Eastern Snake River Plain Aquifer in Idaho. Ureolysis is an integral component of a novel remediation approach for divalent trace metal and radionuclide contaminants in groundwater and associated geomedia, where the contaminants are immobilized by coprecipitation in calcite. The generation of carbonate alkalinity from ureolysis promotes calcite precipitation. In calcite-saturated aquifers, this represents a potential long-term contaminant sequestration mechanism. In a single well experiment, dilute molasses was injected three times over two weeks to promote overall microbial growth, followed by one urea injection. With molasses addition, total cell numbers in the groundwater increased one to two orders of magnitude. Estimated ureolysis rates in recovered groundwater samples increased from <0.1 nmol L-1 hr-1 to >25 nmol L-1 hr-1. A quantitative PCR assay for the bacterial ureC gene indicated that urease gene numbers increased up to 170 times above pre-injection levels. Following urea injection, calcite precipitates were recovered. Estimated values for an in situ first order ureolysis rate constant ranged from 0.016 to 0.057 day-1. The results are promising with respect to the potential to manipulate in situ biogeochemical processes to promote contaminant sequestration.

  12. QUANTUM-STATE RESOLVED PRODUCTS VIA VACUUM ULTRAVIOLET PHOTOSTIMULATED DESORPTION FROM GEOLOIC CALCITE

    EPA Science Inventory

    We report the results of a photostimulated desorption (PSD) study of neutral CO products from room temperature geologic calcite utilizing fluences <300 microJ/cm2 of 157-nm excimer laser radiation. At this wavelength, we are coincident with an intense absorption peak such that m...

  13. Solid solution partitioning of Sr2+, Ba2+, and Cd2+ to calcite

    USGS Publications Warehouse

    Tesoriero, A.J.; Pankow, J.F.

    1996-01-01

    Although solid solutions play important roles in controlling the concentrations of minor metal ions in natural waters, uncertainties regarding their compositions, thermodynamics, and kinetics usually prevent them from being considered. A range of precipitation rates was used here to study the nonequilibrium and equilibrium partitioning behaviors of Sr2+, Ba2+, and Cd2+ to calcite (CaCO3(s)). The distribution coefficient of a divalent metal ion Me2+ for partitioning from an aqueous solution into calcite is given by DMe = (XMeCO3(s)/[Me2+])/(XCaCO3(s)/[Ca 2+]). The X values are solid-phase mole fractions; the bracketed values are the aqueous molal concentrations. In agreement with prior work, at intermediate to high precipitation rates R (nmol/mg-min), DSr, DBa, and DCd were found to depend strongly on R. At low R, the values of DSr, DBa, and DCd became constant with R. At 25??C, the equilibrium values for DSr, DBa, and DCd for dilute solid solutions were estimated to be 0.021 ?? 0.003, 0.012 ?? 0.005, and 1240 ?? 300, respectively. Calculations using these values were made to illustrate the likely importance of partitioning of these ions to calcite in groundwater systems. Due to its large equilibrium DMe value, movement of Cd2+ will be strongly retarded in aquifers containing calcite; Sr2+ and Ba2+ will not be retarded nearly as much.

  14. Re-evaluating boron speciation in biogenic calcite and aragonite using 11

    E-print Network

    Kaufman, Alan Jay

    Re-evaluating boron speciation in biogenic calcite and aragonite using 11 B MAS NMR Kateryna Understanding the partitioning of aqueous boron species into marine carbonates is critical for constraining the boron iso- tope system for use as a marine pH proxy. Previous studies have assumed that boron

  15. NMR surface relaxivity of calcite with adsorbed Mn{sup 2+}

    SciTech Connect

    Kenyon, W.E.; Kolleeny, J.A.

    1995-03-15

    Calcite particles were exposed to Mn{sup 2+} in aqueous solution to allow adsorption. The calcite particles were then packed, and the NMR longitudinal relaxation time T{sub 1} of water saturating the interparticle pores was measured. NMR surface relaxivity was then computed as 1/(T{sub 1}{times}S{sub p}/V{sub p}), where S{sub p}/V{sub p} is the ratio of surface area to pore volume. Adsorbed manganese increases the NMR surface relaxivity to approximately 2.4 {times} 10{sup {minus}3} cm/s, roughly 50 times the surface relaxivity of very pure calcite. Flowing water with 4 {mu}M Mn{sup 2+} through a porous limestone plug decreased its T{sub 1} by a factor of 6. Iron as adsorbate produced relatively small increases in surface relaxivity. These results suggest that manganese dominates the surface relaxivity, of limestone rocks in situ, which is important in the interpretation of NMR borehole logs. Observations suggest that some adsorbed manganese eventually becomes buried by freshly precipitated calcite. In particular, the surface relaxivity increased with initial adsorption, but gradually decreased at long reaction times, even as the aqueous manganese concentration continued to decrease. NMR evidently senses only the manganese in the outermost atomic layer, and thus might prove useful in more detailed studies of adsorption.

  16. Inferences of paleoenvironment from petrographic, chemical and stable-isotope studies of calcretes and fracture calcites

    SciTech Connect

    Vaniman, D.T.; Whelan, J.F.

    1994-03-01

    Past research has indicated a genetic connection between calcite formed in calcretes at the surface of Yucca Mountain, Nevada, and calcites deposited in underlying fractures of the unsaturated zone. This common genesis suggests that paleoenvironmental information, as well as the timing and pathways of past recharge episodes, might be obtained from studies of the deposits in both the calcretes and the unsaturated fractures. Chemical and isotopic modification of calcite-precipitating fluids appears to begin at the surface, largely under the influence of plant roots and their decay products. Chemical characteristics of the deeper calcites are either initiated or largely defined within the first few meters of fluid migration into the unsaturated tuffs beneath the calcretes. However, petrographic and isotopic data indicate a very unique low-{delta}{sup 13}C microenvironment that is localized at the upper surfaces of the calcretes. These surfaces form an interface in the soil horizon where infiltration may pond above the underlying carbonate ``plug.`` In order to decipher the chemistry and petrology of past recharge events, it is important to first understand microenvironments such as this that contribute to mineral precipitation/dissolution events in the pedogenic environment.

  17. Stimulation of microbial urea hydrolysis in groundwater to enhance calcite precipitation.

    PubMed

    Fujita, Yoshiko; Taylor, Joanna L; Gresham, Tina L T; Delwiche, Mark E; Colwell, Frederick S; Mcling, Travis L; Petzke, Lynn M; Smith, Robert W

    2008-04-15

    Addition of molasses and urea was tested as a means of stimulating microbial urea hydrolysis in the Eastern Snake River Plain Aquifer in Idaho. Ureolysis is an integral component of a novel remediation approach for divalent trace metal and radionuclide contaminants in groundwater and associated geomedia, where the contaminants are immobilized by coprecipitation in calcite. Generation of carbonate alkalinity from ureolysis promotes calcite precipitation. In calcite-saturated aquifers, this represents a potential long-term contaminant sequestration mechanism. In a single-well experiment, dilute molasses was injected three times over two weeks to promote overall microbial growth, followed by one urea injection. With molasses addition, total cell numbers in the groundwater increased 1-2 orders of magnitude. Estimated ureolysis rates in recovered groundwater samples increased from < 0.1 to > 25 nmol L(-1) hr(-1). A quantitative PCR assay for the bacterial ureC gene indicated that urease gene numbers increased up to 170 times above pre-injection levels. Following urea injection, calcite precipitates were recovered. Estimated values for an in situ first order ureolysis rate constant ranged from 0.016 to 0.057 d(-1). Although collateral impacts such as reduced permeability were observed, overall results indicated the viability of manipulating biogeochemical processes to promote contaminant sequestration. PMID:18497161

  18. Carbon export and transfer to depth across the Southern Ocean Great Calcite Belt

    NASA Astrophysics Data System (ADS)

    Rosengard, S. Z.; Lam, P. J.; Balch, W. M.; Auro, M. E.; Pike, S.; Drapeau, D.; Bowler, B.

    2015-07-01

    Sequestration of carbon by the marine biological pump depends on the processes that alter, remineralize, and preserve particulate organic carbon (POC) during transit to the deep ocean. Here, we present data collected from the Great Calcite Belt, a calcite-rich band across the Southern Ocean surface, to compare the transformation of POC in the euphotic and mesopelagic zones of the water column. The 234Th-derived export fluxes and size-fractionated concentrations of POC, particulate inorganic carbon (PIC), and biogenic silica (BSi) were measured from the upper 1000 m of 27 stations across the Atlantic and Indian sectors of the Great Calcite Belt. POC export out of the euphotic zone was correlated with BSi export. PIC export was not, but did correlate positively with POC flux transfer efficiency. Moreover, regions of high BSi concentrations, which corresponded to regions with proportionally larger particles, exhibited higher attenuation of > 51 ?m POC concentrations in the mesopelagic zone. The interplay among POC size partitioning, mineral composition, and POC attenuation suggests a more fundamental driver of POC transfer through both depth regimes in the Great Calcite Belt. In particular, we argue that diatom-rich communities produce large and labile POC aggregates, which not only generate high export fluxes but also drive more remineralization in the mesopelagic zone. We observe the opposite in communities with smaller calcifying phytoplankton, such as coccolithophores. We hypothesize that these differences are influenced by inherent differences in the lability of POC exported by different phytoplankton communities.

  19. Unusual biogenic calcite structures in two shallow lakes, James Ross Island, Antarctica

    NASA Astrophysics Data System (ADS)

    Elster, J.; Nedbalová, L.; Vodrážka, R.; Láska, K.; Haloda, J.; Komárek, J.

    2015-08-01

    The floors of two shallow endorheic lakes, located on volcanic surfaces on James Ross Island, are covered with calcareous organosedimentary structures. Their biological and chemical composition, lake water characteristics, and seasonal variability of the thermal regime are introduced. The lakes are frozen down to the bottom eight-nine months per year and their water chemistry is characterized by low conductivity and neutral to slightly alkaline pH. The photosynthetic microbial mat is composed of filamentous cyanobacteria and microalgae that are considered to be Antarctic endemic species. The mucilaginous black biofilm is covered by green spots formed by a green microalga and the macroscopic structures are packed together with fine material. Thin sections consist of rock substrate, soft biofilm, calcite spicules and mineral grains originating from different sources. The morphology of the spicules is typical of calcium carbonate monocrystals having a layered structure and worn surface, which reflect growth and degradation processes. The spicules chemical composition and structure correspond to pure calcite. Lakes age, altitude, morphometry, geomorphological and hydrological stability, including low sedimentation rates, together with thermal regime predispose the existence of this community. We hypothesize that the precipitation of calcite is connected with the photosynthetic activity of the green microalgae that were not recorded in any other lake in the region. This study has shown that the unique community producing biogenic calcite spicules is quite different to any yet described.

  20. Mechanics, microstructure and AMS evolution of a synthetic porphyritic calcite aggregate deformed in torsion

    NASA Astrophysics Data System (ADS)

    Marques, F. O.; Machek, M.; Roxerová, Z.; Burg, J.-P.; Almqvist, B. S. G.

    2015-08-01

    In order to investigate the mechanical, microstructural and AMS evolution of porphyritic mylonites, we made a synthetic aggregate composed of 70% fine calcite (< 50 ?m) and 30% coarse calcite (200-700 ?m), and deformed cylindrical specimens in torsion at 300 MPa, 727 °C, a constant strain rate of 3.0E- 4 s- 1, to shear strains ? ? 1 and 5. After peak stress, dynamic recrystallization of porphyroclasts resulted in grain size reduction and weakening till a mechanical steady state was reached. Microstructural, AMS and EBSD analyses show the consistent evolution of pre-torsion (cold-pressed) planar fabric from perpendicular to sample cylinder axis at ? ? 0, to oblique at ? ? 1, and finally to low angle to the shear plane at ? ? 5, as expected for approximate simple shear. At ? ? 1, stretched calcite grains > 3 mm in length defined a conspicuous foliation, and showed aligned twins. At ? ? 5, calcite porphyroclasts were highly stretched (aspect ratio around 20), and had rotated towards the shear plane. Between ? = 1 and 5, a composite fabric formed, one at low and the other at high angle to the shear plane, from which shear sense can be deduced. The AMS patterns were sensitive to increasing shearing, and tracked strain reasonably well, despite the reduced size and low susceptibility of specimens. From the CPO and the microstructure, we infer that a balance compatible with an optimal dissipation of the applied stress was achieved between grain growth and grain reduction processes.

  1. Imaging crystal orientations in multicrystalline silicon wafers via photoluminescence

    E-print Network

    Imaging crystal orientations in multicrystalline silicon wafers via photoluminescence H. C. Sio, Z-mediated nonclassical crystal growth of sodium fluorosilicate nanowires and nanoplates AIP Advances 1, 042165 (2011) Crystal phase and growth orientation dependence of GaAs nanowires on NixGay seeds via vapor

  2. A model for microbially induced precipitation of vadose-zone calcites in fractures at LOS Alamos, New Mexico, USA

    NASA Astrophysics Data System (ADS)

    Newman, Brent D.; Campbell, Andrew R.; Norman, David I.; Ringelberg, David B.

    1997-05-01

    Fractures are unique environments that can concentrate the flow of water, nutrients, and contaminants. As such, fractures play an important role in controlling the flux of various substances into and through the vadose zone. Calcite fracture fillings are present in the near surface in the Bandelier Tuff Formation at Los Alamos, New Mexico, and provide a record of the geochemical and hydrologic processes that have occurred in fractures. The objective of this study was to examine calcite fracture fills in order to improve understanding of processes within fractures, and in particular those that lead to precipitation of calcite. Samples of calcite fillings were collected from vertical and horizontal fractures exposed in a shallow waste-burial pit. Scanning electron microscopy show morphologies which suggest that plants, fungi, and bacteria were important in the precipitation process. Quadrupole mass spectrometric analyses of fluid inclusion gases show predominantly methane (17-99%) and little to no oxygen (0-8%), suggesting the development of anaerobic conditions in the fractures. Ester-linked phospholipid biomarkers are evidence for a diverse microbial community in the fractures, and the presence of di-ether lipids indicate that the methane was generated by anaerobic bacteria. The calcite fillings apparently resulted from multiple biological and chemical processes in which plant roots in the fractures were converted to calcite. Roots grew into the fractures, eventually died, and were decomposed by bacteria and fungi. Anaerobic gases were generated from encapsulated organic material within the calcite via microbial decomposition, or were generated by microbes simultaneously with calcite precipitation. It is likely that the biological controls on calcite formation that occurred in the Los Alamos fractures also occurs in soils, and may explain the occurrence of other types of pedogenic calcites.

  3. The kinetics of clumped-isotope reactions in calcite and apatite from natural and experimental samples

    NASA Astrophysics Data System (ADS)

    Stolper, D. A.; Eiler, J. M.

    2014-12-01

    Measurements of clumped isotopes of carbonate-bearing minerals are a powerful tool for reconstructing past surface temperatures and thermal histories of shallow crustal rocks. Because the clumped-isotope thermometer is based on homogenous-phase equilibrium, a sample's clumped-isotope temperature is susceptible to resetting through, for example, intracrystalline diffusion and redistribution of C and O isotopes during (re)heating or slow cooling. Quantitative knowledge of the kinetics of this resetting have received increasing attention (1-3) and is critical for understanding the meaning of clumped-isotope temperatures of samples with complex burial histories. To better constrain these kinetics and complement previous work (1-3) we performed heating experiments (400-700°C) on optical calcites and carbonate-bearing apatites. As previously observed (2-3), calcites exhibit non-first-order kinetics. The data were fit using a model that incorporates both diffusion and isotope-exchange reactions (4). The kinetics derived with this model using the optical-calcite heating experiments of (2) and those measured here are indistinguishable. The model predicts that subtle changes (>10°C) in measured calcite clumped-isotope temperatures can occur at burial temperatures between 60-100°C on million-year timescales. Though small, such changes may have an impact on clumped-isotope-based reconstructions of past surface temperatures and thermal histories. The derived kinetics were compared to clumped-isotope measurements of cogenetic calcites and apatites from slowly cooled carbonatite intrusions. Apparent temperatures are 70-140°C for apatites and 120-190°C for calcites. Measured temperatures for calcites match modeled temperatures using reasonable geological cooling rates. Natural apatite samples yield lower apparent temperatures than predicted based on the model. We propose that this difference is the result of annealment of structural damage in apatites (e.g., generated by radiation damage) during experiments. (1) Dennis and Schrag, 2010; (2) Passey and Henkes, 2012; (3) Henkes et al., 2014. (4) Zhang et al., 1995.

  4. Controls on modern speleothem calcite growth in a central Texas cave and implications for paleoclimate reconstruction

    NASA Astrophysics Data System (ADS)

    Hatch, R. L.; Banner, J. L.; Wong, C.

    2013-12-01

    A 12-year monitoring study in a central Texas cave provides insight into the seasonal controls on modern calcite growth. Speleothems, or cave calcite deposits, are commonly used as climate proxies due to their ability to record paleoenvironmental change. Speleothem trace element ratios, such as Mg/Ca, Sr/Ca and Ba/Ca, are one type of speleothem proxy used to reconstruct relative rainfall variations. To interpret past rainfall variations from speleothem trace element ratios, the processes controlling the incorporation of drip-water trace elements into speleothem calcite must be known. Growth rate, saturation state, and temperature are all factors that have the potential to influence trace element partitioning coefficients. This study compares the variables controlling calcite growth with the factors controlling dripwater trace element ratios in order to better interpret speleothem records. While the factors controlling growth rate are well established theoretically, observing the system empirically enables the assessment of the relative dominance of each factor on calcite growth rates. Cave-air temperature and CO2 concentrations, relative humidity and drip rate were measured each month at multiple drip sites in Natural Bridge Caverns, central Texas beginning in 2001. Artificial substrates (glass-plates) were placed at five of these sites and collected monthly to determine growth rate. While previous studies have determined changes in substrate calcite growth rate are driven by drip rate (primarily) and density-driven ventilation of cave-air CO2 (secondarily), the research here focuses on how variations in dripwater trace element ratios are related to variations in calcite growth. Dripwaters at three sites in Natural Bridge (NBBC, NBCT and NBWS) were analyzed for Mg/Ca, Sr/Ca and Ba/Ca ratios to determine the relationship between trace elements in drip water and the parameters affecting calcite growth rate. At site NBBC, growth rate is negatively correlated with CO2 concentrations (r2=0.48, p<0.01) and outside air temperatures (r2=0.25, p<0.01), reflecting enhanced calcite growth rates related to the seasonal ventilation in cave-air CO2 concentrations driven by differences between surface- and cave-air temperatures. At NBCT growth rate is correlated to drip rate (r2=0.21, p<0.01) as well as dripwater trace elements (r2=0.35, p<0.01). At NBWS, neither growth nor trace element ratios are significantly correlated to any of the measured physical parameters. The relationships observed in this study are important in understanding speleothem trace element changes where variations in both CO2 and rainfall have the potential to influence the dripwater chemistry. These findings could indicate a bias towards higher trace element ratios in the season of calcite growth whether the primary control on growth is rainfall or CO2 ventilation.

  5. A role for seed storage proteins in Arabidopsis seed longevity

    PubMed Central

    Nguyen, Thu-Phuong; Cueff, Gwendal; Hegedus, Dwayne D; Rajjou, Loïc; Bentsink, Leónie

    2015-01-01

    Proteomics approaches have been a useful tool for determining the biological roles and functions of individual proteins and identifying the molecular mechanisms that govern seed germination, vigour and viability in response to ageing. In this work the dry seed proteome of four Arabidopsis thaliana genotypes, that carry introgression fragments at the position of seed longevity quantitative trait loci and as a result display different levels of seed longevity, was investigated. Seeds at two physiological states, after-ripened seeds that had the full germination ability and aged (stored) seeds of which the germination ability was severely reduced, were compared. Aged dry seed proteomes were markedly different from the after-ripened and reflected the seed longevity level of the four genotypes, despite the fact that dry seeds are metabolically quiescent. Results confirmed the role of antioxidant systems, notably vitamin E, and indicated that protection and maintenance of the translation machinery and energy pathways are essential for seed longevity. Moreover, a new role for seed storage proteins (SSPs) was identified in dry seeds during ageing. Cruciferins (CRUs) are the most abundant SSPs in Arabidopsis and seeds of a triple mutant for three CRU isoforms (crua crub cruc) were more sensitive to artificial ageing and their seed proteins were highly oxidized compared with wild-type seeds. These results confirm that oxidation is involved in seed deterioration and that SSPs buffer the seed from oxidative stress, thus protecting important proteins required for seed germination and seedling formation. PMID:26184996

  6. A role for seed storage proteins in Arabidopsis seed longevity.

    PubMed

    Nguyen, Thu-Phuong; Cueff, Gwendal; Hegedus, Dwayne D; Rajjou, Loïc; Bentsink, Leónie

    2015-09-01

    Proteomics approaches have been a useful tool for determining the biological roles and functions of individual proteins and identifying the molecular mechanisms that govern seed germination, vigour and viability in response to ageing. In this work the dry seed proteome of four Arabidopsis thaliana genotypes, that carry introgression fragments at the position of seed longevity quantitative trait loci and as a result display different levels of seed longevity, was investigated. Seeds at two physiological states, after-ripened seeds that had the full germination ability and aged (stored) seeds of which the germination ability was severely reduced, were compared. Aged dry seed proteomes were markedly different from the after-ripened and reflected the seed longevity level of the four genotypes, despite the fact that dry seeds are metabolically quiescent. Results confirmed the role of antioxidant systems, notably vitamin E, and indicated that protection and maintenance of the translation machinery and energy pathways are essential for seed longevity. Moreover, a new role for seed storage proteins (SSPs) was identified in dry seeds during ageing. Cruciferins (CRUs) are the most abundant SSPs in Arabidopsis and seeds of a triple mutant for three CRU isoforms (crua crub cruc) were more sensitive to artificial ageing and their seed proteins were highly oxidized compared with wild-type seeds. These results confirm that oxidation is involved in seed deterioration and that SSPs buffer the seed from oxidative stress, thus protecting important proteins required for seed germination and seedling formation. PMID:26184996

  7. Influence of calcite and dissolved calcium on uranium(VI) sorption to a hanford subsurface sediment.

    PubMed

    Dong, Wenming; Ball, William P; Liu, Chongxuan; Wang, Zheming; Stone, Alan T; Bai, Jing; Zachara, John M

    2005-10-15

    The influence of calcite and dissolved calcium on U(VI) adsorption was investigated using a calcite-containing sandy silt/clay sediment from the U. S. Department of Energy Hanford site. U(VI) adsorption to sediment, treated sediment, and sediment size fractions was studied in solutions that both had and had not been preequilibrated with calcite, at initial [U(VI)] = 10(-7)-10(-5) mol/L and final pH = 6.0-10.0. Kinetic and reversibility studies (pH 8.4) showed rapid sorption (30 min), with reasonable reversibility in the 3-day reaction time. Sorption from solutions equilibrated with calcite showed maximum U(VI) adsorption at pH 8.4 +/- 0.1. In contrast, calcium-free systems showed the greatest adsorption at pH 6.0-7.2. At pH > 8.4, U(VI) adsorption was identical from calcium-free and calcium-containing solutions. For calcite-presaturated systems, both speciation calculations and laser-induced fluorescence spectroscopic analyses indicated that aqueous U(VI) was increasingly dominated by Ca2UO2(CO3)3(0)(aq) at pH < 8.4 and thatformation of Ca2UO2(CO3)3(0)(aq) is what suppresses U(VI) adsorption. Above pH 8.4, aqueous U(VI) speciation was dominated by UO2(CO3)3(4-) in all solutions. Finally, results also showed that U(VI) adsorption was additive in regard to size fraction but not in regard to mineral mass: Carbonate minerals may have blocked U(VI) access to surfaces of higher sorption affinity. PMID:16295860

  8. Visualizing Organophosphate Precipitation at the Calcite-Water Interface by in Situ Atomic-Force Microscopy.

    PubMed

    Wang, Lijun; Qin, Lihong; Putnis, Christine V; Ruiz-Agudo, Encarnación; King, Helen E; Putnis, Andrew

    2016-01-01

    Esters of phosphoric acid constitute a large fraction of the total organic phosphorus (OP) in the soil environment and, thus, play an important role in the global phosphorus cycle. These esters, such as glucose-6-phosphate (G6P), exhibit unusual reactivity toward various mineral particles in soils, especially those containing calcite. Many important processes of OP transformation, including adsorption, hydrolysis, and precipitation, occur primarily at mineral-fluid interfaces, which ultimately governs the fate of organophosphates in the environment. However, little is known about the kinetics of specific mineral-surface-induced adsorption and precipitation of organophosphates. Here, by using in situ atomic-force microscopy (AFM) to visualize the dissolution of calcite (1014) faces, we show that the presence of G6P results in morphology changes of etch pits from the typical rhombohedral to a fan-shaped form. This can be explained by a site-selective mechanism of G6P-calcite surface interactions that stabilize the energetically unfavorable (0001) or (0112) faces through step-specific adsorption of G6P. Continuous dissolution at calcite (1014)-water interfaces caused a boundary layer at the calcite-water interface to become supersaturated with respect to a G6P-Ca phase that then drives the nucleation and growth of a G6P-Ca precipitate. Furthermore, after the introduction of the enzyme alkaline phosphatase (AP), the precipitates were observed to contain a mixture of components associated with G6P-Ca, amorphous calcium phosphate (ACP)-hydroxyapatite (HAP) and dicalcium phosphate dihydrate (DCPD). These direct dynamic observations of the transformation of adsorption- and complexation-surface precipitation and enzyme-mediated pathways may improve the mechanistic understanding of the mineral-interface-induced organophosphate sequestration in the soil environment. PMID:26636475

  9. Influence of Calcite and Dissolved Calcium on Uranium(VI) Sorption to a Hanford Subsurface Sediment

    SciTech Connect

    Dong, Wenming; Ball, William P.; Liu, Chongxuan; Wang, Zheming; Stone, Alan T.; Bai, Jing; Zachara, John M.

    2005-10-15

    The influence of calcite and dissolved calcium on U(VI) adsorption was investigated using a calcite-containing sandy silt/clay sediment from the U. S. Department of Energy Hanford site. U(VI) adsorption to sediment, treated sediment, and sediment size fractions was studied in solutions that both had and had not been preequilibrated with calcite, at initial [U(VI)] - 10-7-10-5 mol/L and final pH - 6.0-10.0. Kinetic and reversibility studies (pH 8.4) showed rapid sorption (30 min), with reasonable reversibility in the 3-day reaction time. Sorption from solutions equilibrated with calcite showed maximum U(VI) adsorption at pH 8.4-0.1. In contrast, calcium-free systems showed the greatest adsorption at pH 6.0-7.2. At pH > 8.4, U(VI) adsorption was identical from calcium-free and calcium-containing solutions. For calcite-presaturated systems, both speciation calculations and laser-induced fluorescence spectroscopic analyses indicated that aqueous U(VI) was increasingly dominated by Ca2UO2(CO3)3 0(aq) at pH<8.4 and that formation of Ca2UO2(CO3)3 0(aq) is what suppresses U(VI) adsorption. Above pH 8.4, aqueous U(VI) speciation was dominated by UO2(CO3)3 4- in all solutions. Finally, results also showed that U(VI) adsorption was additive in regard to size fraction but not in regard to mineral mass: Carbonate minerals may have blocked U(VI) access to surfaces of higher sorption affinity.

  10. Fault evolution in the North Peloponnese inferred from calcite dating and syntectonic sedimentary characteristics

    NASA Astrophysics Data System (ADS)

    Causse, C.; Moretti, I.; Eschard, R.; Micarelli, L.

    2003-04-01

    The evolution of the Gulf of Corinth is often described as a two phases process with a slow first phase and a second fast one from Late Pliocene to now. Other authors propose a simple tectonic history of Corinth Rift as a continuous sequence from 900 ka and present time with a progressive migration of the tectonic activity from South to North. New field observations and dating of calcite cements collected from various faults allow us to present a more complex scenario. Calcite cements were precisely selected in order to date only true cement, related to the current opening. Fragments of calcite breccia or host rocks have been rejected. Th/U dating was obtained by TIMS measurements on calcite containing at least 50 ppb of uranium in order to limit the sample size (2 to 4 grams) and insure the true selection of pure cement. Precise sedimentary logs have been done close to the faults in order to decipher between post and syntectonic deposit related to each fault. Some outcrops are older than 1 Ma, showing 230Th/234U and 234U/238U ratios equilibrated, other are older than 600 ka and younger than 1 Ma, with 230Th/234U ratios equilibrated and 234U/238U ratios presenting excess of 234U. Two sites have delivered younger ages around 120 ka. A particular emphasis will be put on Doumena Fault, located south of Pirgaki Fault, which appears, from sedimentological data, post-sedimentation. A calcite cement has been dated at 125 ka by Th/U disequilibrium, assessing a tectonic phase practically contemporaneous. It means that this fault is clearly younger than the Pirgaki and hence out-of-sequence in a classical model that implies a progressive migration from south to north.

  11. Crystallization Screens Crystallization Optimization

    E-print Network

    Lebendiker, Mario

    a local start-up company into an established business with a glo- bal distribution network. We deliver crystallization. High quality reagents and excellent customer service help the researcher to find tailor of tools for protein crystallization. High quality reagents and excellent customer service help

  12. NC-AFM contrast formation on the calcite ( ) surface This article has been downloaded from IOPscience. Please scroll down to see the full text article.

    E-print Network

    Kühnle, Angelika

    NC-AFM contrast formation on the calcite ( ) surface This article has been downloaded from.1088/0953-8984/24/8/084006 NC-AFM contrast formation on the calcite (10¯14) surface Philipp Rahe, Jens Sch¨utte1 and Angelika K Published 7 February 2012 Online at stacks.iop.org/JPhysCM/24/084006 Abstract Calcite, the most stable

  13. PII S0016-7037(01)00836-5 Climate proxies from Sr/Ca of coccolith calcite: Calibrations from continuous culture of

    E-print Network

    Falkowski, Paul G.

    PII S0016-7037(01)00836-5 Climate proxies from Sr/Ca of coccolith calcite: Calibrations from.5 divisions per day and calcification rate increased from 1.5 to 50 pg calcite per cell per day. When foraminifera and abiogenic calcites, suggesting that it is controlled by thermodynamic processes. However

  14. doi:10.1016/j.gca.2004.12.019 Nanoscale effects of strontium on calcite growth: An in situ AFM study in the absence of

    E-print Network

    Dove, Patricia M.

    doi:10.1016/j.gca.2004.12.019 Nanoscale effects of strontium on calcite growth: An in situ AFM growth of calcite at various levels of superaturation and fluid Sr concentrations. Our results show may be associated with slight shifts in calcite solubility when Sr is incorporated or may be due

  15. doi:10.1016/j.gca.2005.04.006 Effects of temperature and transport conditions on calcite growth in the presence of Mg2

    E-print Network

    Dove, Patricia M.

    doi:10.1016/j.gca.2005.04.006 Effects of temperature and transport conditions on calcite growth) Abstract--This study links direct measurement of Mg-calcite growth kinetics with high on Mg partitioning into calcite, here the layer-growth mechanism was observed in situ and step speeds

  16. Organic carbon flux and organic carbon to calcite flux ratio recorded in deep-sea carbonates: Demonstration and a new proxy

    E-print Network

    Organic carbon flux and organic carbon to calcite flux ratio recorded in deep-sea carbonates; published XX Month 2002. [1] Theoretical considerations indicate that degree of bottom water calcite saturation, organic carbon flux, and the ratio of that flux to the calcite flux all are reflected

  17. In situ 18O and Mg/Ca analyses of diagenetic and planktic foraminiferal calcite preserved in a deep-sea record

    E-print Network

    Meyers, Stephen R.

    In situ 18O and Mg/Ca analyses of diagenetic and planktic foraminiferal calcite preserved in a deep.8 higher than that of planktic foraminiferal calcite (À3.6 PDB), while crystallite Mg/Ca and Sr/Ca ratios are slightly higher and substantially lower than in planktic foraminiferal calcite, respectively. The focused

  18. delta. sup 18 O values, sup 87 Sr/ sup 86 Sr and Sr/Mg ratios of Late Devonian abiotic marine calcite: Implications for the composition of ancient seawater

    SciTech Connect

    Carpenter, S.J.; Lohmann, K.C.; Walter, L.M.; Huston, J.G.; Halliday, A.N. ); Holden, P. )

    1991-07-01

    Late Devonian (Frasnian) abiotic marine calcite has been microsampled and analyzed for {sup 87}Sr/{sup 86}Sr ratios, {delta}{sup 18}O and {delta}{sup 13}C values, and minor element concentrations. Portions of marine cement crystals from the Alberta and Canning Basins have escaped diagenetic alteration and preserve original marine {delta}{sup 18}O values ({minus}4.8{per thousand} {plus minus} 0.5, PDB), {delta}{sup 13}C values (+2.0 to +3.0{per thousand}, PDB), {sup 87}Sr/{sup 86}Sr ratios (0.70805 {plus minus} 3), and Sr/Mg weight ratios (0.04 to 0.05). Marine {sup 87}Sr/{sup 86}Sr 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 {delta}{sup 18}O values which are 3 to 4{per thousand} lower than those of modern marine cements. These low {delta}{sup 18}O values are best explained by precipitation from {sup 18}O-depleted seawater and not be elevated seawater temperature or diagenetic alteration. For comparison with Devonian data, analogous data were collected from Holocene Mg-calcite and aragonite marine cements from Enewetak Atoll, Marshall Islands. Mg-calcite and aragonite marine cements are in isotopic equilibrium with ambient seawater, and Mg-calcite cements are homogeneous with respect to Sr and Mg contents. Comparison of Sr and Mg contents of analogous Devonian and Holocene marine cements suggests that the Mg/Ca ratio of Late Devonian seawater was significantly lower and that the Sr/Ca ratio was significantly higher than that of modern seawater.

  19. A quick SEED tutorial

    USGS Publications Warehouse

    Ringler, Adam; Evans, John R.

    2015-01-01

    A number of different government-funded seismic data centers offer free open-access data (e.g., U.S. Geological Survey, National Earthquake Information Center, the Incorporated Research Institutions for Seismology (IRIS), and Data Management System), which can be freely downloaded and shared among different members of the community (Lay, 2009). To efficiently share data, it is important that different data providers follow a common format. The Standard for the Exchange of Earthquake Data (SEED) provides one such format for storing seismic and other geophysical data. The SEED format is widely used in earthquake seismology; however, SEED and its structure can be difficult for many first-time users (ourselves included). Below is a quick tutorial that outlines the basic structure of SEED format. This write-up is in no way intended to replace the comprehensive SEED manual (Ahern et al., 2009), and instead of going into the details of any specific part of the SEED format we refer the reader to the manual for additional details. The goal of this write-up is to succinctly explain the basic structure of SEED format as well as the associated jargon, as most commonly used now, in a colloquial way so that novice users of SEED can become more familiar with the format and its application quickly. Our goal is to give the reader the necessary background so that when problems or questions about SEED format arise they will have some understanding of where they should look for more details or from where the problem might be stemming. As a secondary goal, we hope to help the reader become familiar with the SEED manual (Ahern et al., 2009), which contains detailed information about all aspects of the SEED format.

  20. Examining Children's Models of Seed.

    ERIC Educational Resources Information Center

    Jewell, Natalie

    2002-01-01

    Reports research that examines children's models of seed. Explores the conceptions held by children (N=75) of germination and seed formation. Concludes that children hold a restricted meaning for the term 'seed'. (DDR)