Sample records for calcite seed crystals

  1. 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...

  2. Inhibition by glycosaminoglycans of CaCO3 (calcite) crystallization.

    PubMed Central

    Grant, D; Long, W F; Williamson, F B

    1989-01-01

    Of a range of glycosaminoglycans, heparin and heparan sulphate were the most effective inhibitors in vitro of CaCO3 (calcite) crystallization as assayed by conductimetric measurements. The possible role of such glycosaminoglycans in modulating calcium-salt crystallizations in vivo is discussed. PMID:2719649

  3. Structure and mechanical properties of biogenic single calcite crystals

    NASA Astrophysics Data System (ADS)

    Aizenberg, Joanna; Weiner, Steve; Addadi, Lia

    2000-03-01

    Composite materials, in which the organic host is stiffened by guest crystalline particles, are widely used in nature (bones, teeth, mollusk shells) and are produced synthetically by man (fiber-reinforced composites). Organisms also produce a different type of composite in which the host is a single crystal and the guests are macromolecules occluded in an orderly fashion within the crystal. The best-studied examples, to date, are skeletal elements composed of a single calcite crystal. These skeletons have unique mechanical properties, and fracture with a glassy conchoidal surface, which is quite different from the smooth planar cleavage of pure calcite. The specific positions of macromolecules in calcite crystals were identified by in vitro crystallization experiments and synchrotron X-ray studies. We show that the occluded macromolecules introduced specifically along crystallographic planes that are oblique to the cleavage planes of calcite strengthen the material against failure by both absorbing and deviating the advancing cracks. These novel, "reverse" fiber-reinforced, composites may be just one example of strategies used in nature for producing materials with improved properties.

  4. Mass transfer of reactive crystallization in synthesizing calcite nanocrystal

    Microsoft Academic Search

    Rong-yi Lin; Jia-yun Zhang; Yuan-qiang Bai

    2006-01-01

    An experimental study on the mass transfer and reactive crystallization of calcite nanocrystal was carried out in a Na5P3O10–Ca(OH)2–CO2–H2O multiphase system. According to the two-film theory and the two-steps crystal growth model, the kinetic characteristics in the system were investigated by the rate-comparison of the calcium hydroxyl dissolution, carbon dioxide absorption and calcium carbonate precipitation. The result indicated that the

  5. Rapid supercritical CO2 fluid migration in calcite crystals

    NASA Astrophysics Data System (ADS)

    Zuddas, Pierpaolo; Lopez, Olivier; Salvi, Stefano

    2010-05-01

    The transport of supercritical fluids is a determining factor for several geological processes as well fundamental in predicting natural resource accumulation and distribution. Calcite, ubiquitous in geological environments may contain supercritical CO2 trapped under fluid inclusions commonly assumed to remain static under ambient conditions. Here, we report nano-meter scale observations on calcite crystal surface indicating the occurrence of fast movement of supercritical CO2 fluid inclusions hosted in the upper part of calcite crystals. Real time monitoring of calcite samples without observable presence of fluid inclusions, by in-situ Atomic Force Microscopy (AFM), shows a flat state of the calcite surface (after freshly cleaving) and the surface state condition did not change during several hours of scanning. However, AFM observations on calcite samples with visible fluid inclusions show rapid formation of nanometre-scale hillocks spontaneously formed on the surface structure of the calcite. They have an averaged height of 1 nm, and varied horizontal dimensions and geometries. The fact that hillocks formed spontaneously on flat terraces in only a few minutes, without evidence of surface dissolution, was unexpected and suggests that the source of hillock material should be derived within the crystal itself. This phenomenon was observed even changing the experimental conditions such a scan frequency of the AFM tip, environmental temperature (between 5° and 50°C) and the surface area of scanning. The observed hillocks can form by the fact that CO2-rich fluid inclusions located just under the mineral surface are at elevated internal pressure and near the rupture limit. Thus, a frail mechanical strain can case them to decrepitated and lose their fluid. Upon reaching the surface, the supercritical CO2 leaked from the fluid inclusions, mixes with the thin water layer in equilibrium with ambient CO2 partial pressure at the calcite surface, causing degassing of CO2 and facilitating calcite precipitation in the form of hillocks. We estimated CO2 supercritical fluid transport assuming a minimum depth of the fluid inclusions involved in the fluid movement and an instantaneous precipitation at the surface. We found that supercritical CO2 fluid transport in calcite is around the value of 10 nm/s. The estimated fast fluid transport rate is about 10 orders of magnitude higher than the estimated low-temperature extrapolation of solid-state diffusion vacancy in calcite crystals. Classical description of fluid transport recognises several distinct paths only for polycrystalline materials assuming the presence of inter-grain pathways as micro and nano-pore tubes. Fluid transport is usually observed in poly-phase material grains can also exhibit clear indications of multi-path migration even when visible evidence of such paths is lacking. Our study quantifies this process in the case of natural calcite at external standard conditions and be of potential importance in movement of CO2 rich fluids under supercritical conditions.

  6. 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.

  7. Nanoripples formation in calcite and indium phosphide (InP) single crystals

    Microsoft Academic Search

    Ramakrishna Gunda

    2007-01-01

    In this project we studied the formation of nanoripples in calcite and InP single crystals by continuous scanning using the nanoindenter in the ambient environment and by Argon ion irradiation under ultra high vacuum conditions, respectively. Formation of tip induced nanowear ripples is studied on a freshly cleaved calcite single crystal as a function of scanning frequency and contact load

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

    PubMed Central

    Murai, Rie

    2013-01-01

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

  9. 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.

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

    SciTech Connect

    Jones, B. [Univ. of Alberta, Edmonton, Alberta (Canada). Dept. of Earth and Atmospheric Sciences; Renault, R.W. [Univ. of Saskatchewan, Saskatoon, Saskatchewan (Canada). Dept. of Geological Sciences

    1998-09-01

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

  11. 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.

  12. Skeletal crystals of calcite and trona from hot-spring deposits in Kenya and New Zealand

    SciTech Connect

    Jones, B. [Univ. of Alberta, Edmonton, Alberta (Canada). Dept. of Earth and Atmospheric Sciences; Renaut, R.W. [Univ. of Saskatchewan, Saskatoon, Saskatchewan (Canada). Dept. of Geological Sciences

    1996-01-01

    Skeletal crystals are hollow crystals that develop because their outer walls grow before their cores. The presence of skeletal crystals of calcite (three types--trigonal prisms, hexagonal prisms, and plates) and trona in hot (> 90 C) spring deposits in New Zealand (Waikite Springs and Ohaaki Pool) and Kenya (Lorusio hot springs) shows that they can form in natural sedimentary regimes. Analysis of samples from these deposits shows that this crystal morphology develops under disequilibrium conditions that are unrelated to a specific environmental or diagenetic setting. Skeletal crystals transform into solid crystals when subsequent precipitation fills their hollow cores. In some cases, this may involve precipitation of crystalline material that has a sieve-like texture. In other examples, the skeletal crystal provides a framework upon which other materials can be precipitated. Walls in the skeletal trigonal calcite prisms from Waikite Springs are formed of subcrystals that mimic the shape of the parent crystal. Similarly, plate-like skeletal crystals from Lorusio are formed of densely packed subcrystals that are < 0.5 {micro}m long. Conversely, the walls of the skeletal hexagonal calcite crystals from Ohaaki Pool and the skeletal trona crystals from Lorusio are not formed of subcrystals. Recognition of skeletal crystals is important because they represent growth that follows the reverse pattern of normal growth. Failure to recognize that crystal growth followed the skeletal motif may lead to false interpretations concerning the growth of a crystal.

  13. 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 and SEM imaging techniques. Figure S2. Calcite crystals nucleated and grown on Kevlar threads on Kevlar threads in the presence of 100 µM AP7N in solution. Again surface morphology is altered compared

  14. The interaction of magnesium with calcite during crystal growth at 25-90°C and one atmosphere

    Microsoft Academic Search

    Amitai Katz

    1973-01-01

    Calcite crystals were grown in a closed system by recrystallization of synthetic and natural aragonite crystals, in the presence of various CaCl 2 -MgCl 2 solutions with and without NaCl. The distribution of Mg 2+ between calcite and solution at the entire temperature range is heterogeneous, closely following the ( and , 1925) distribution law. Mg 2+ C is strongly

  15. Anisotropic surface coupling while sliding on dolomite and calcite crystals

    NASA Astrophysics Data System (ADS)

    Pina, Carlos M.; Miranda, Rodolfo; Gnecco, Enrico

    2012-02-01

    High-resolution friction force microscopy has been performed on the (104) surfaces of dolomite and calcite in deionized water. The two rows of oxygen atoms alternating in a zigzag way on top of both surfaces are resolved with similar contrast while scanning along the [421¯] direction. Along the [010] direction, only one row is resolved, provided that the normal loading is large enough. The direction-dependent interaction between the probing tip and surface atoms is explained by numeric calculations based on the Prandtl-Tomlinson model.

  16. Calcite Single Crystals as Hosts for Atomic-Scale Entrapment and Slow Release of Drugs.

    PubMed

    Magnabosco, Giulia; Giosia, Matteo Di; Polishchuk, Iryna; Weber, Eva; Fermani, Simona; Bottoni, Andrea; Zerbetto, Francesco; Pelicci, Pier Giuseppe; Pokroy, Boaz; Rapino, Stefania; Falini, Giuseppe; Calvaresi, Matteo

    2015-07-01

    Doxorubicin (DOX)/CaCO3 single crystals act as pH responsive drug carrier. A biomimetic approach demonstrates that calcite single crystals are able, during their growth in the presence of doxorubicin, to entrap drug molecules inside their lattice along specific crystallographic directions. Alterations in lattice dimensions and microstructural parameters are determined by means of high-resolution synchrotron powder diffraction measurements. Confocal microscopy confirms that doxorubicin is uniformly embedded in the crystal and is not simply adsorbed on the crystal surface. A slow release of DOX was obtained preferentially in the proximity of the crystals, targeting cancer cells. PMID:26033854

  17. 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, 2009 (received for review October 13, 2008) The sea urchin tooth is a remarkable grinding tool. Even in the field of biomin- eralization is the ability of the sea urchin tooth to grind down limestone, because

  18. Anomalous Transmission of Thermally Scattered X-Rays in Calcite Crystal

    NASA Astrophysics Data System (ADS)

    Kashiwase, Yasuji; Kainuma, Yoshiro

    1982-08-01

    An excess line was observed across the 200 diffuse spot on Laue photograph of calcite crystal by using unfiltered radiation from copper target operated at accelerating voltage 30 kV. The line is explained to be caused by anomalous transmission of the thermally scattered characteristic X-rays.

  19. 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.

  20. 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 10mN/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 6h. The amorphous CaCO3 was transformed to rod-like single crystal calcite crystals at an extended crystallization time of 12h and 24h, 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

  1. Trigonal dendritic calcite crystals forming from hot spring waters at Waikite, North Island, New Zealand

    SciTech Connect

    Jones, B.; Renault, R.W.; Rosen, M.R.

    2000-05-01

    Amorphous silica and calcite form the deposits in the vent and on the discharge apron of Waikite Spring 100 (WS-100), which is located in the Waikite Geothermal area on North Island, New Zealand. These precipitates formed from spring water that has a temperature of >90 C and a pH of 8.1--8.8. The opaline silica is restricted to areas around the vent where cooling and evaporation of the spring water triggered precipitation. The calcite deposits in the spring vent and on the discharge apron are formed of large (up to 15 cm long) asymmetrical dendrite crystals that are characterized by multiple levels of branching. Branches grew preferentially from the downflow side of their parent branch. All branches have a trigonal transverse cross section except in areas where competition for growth space induced merger of neighboring crystals. The primary branches of the dendrite crystals are (sub)perpendicular to the substrate even in areas where the discharge apron slopes at a high angle (up to 80{degree}). On the steeper parts of the discharge apron, the plate-like primary branches form the floors of the small terrace pools whereas their distal edges form the rims of the pools. Growth of these dendrite crystals is attributed to abiotic processes. High levels of saturation with respect to calcite were caused by rapid CO{sub 2} degassing of the sheets of spring water that flowed down the steep discharge apron. Calcite crystals with different crystal morphologies characterize other springs near this spring. The variation in crystal morphologies from spring to spring is attributed to different levels of saturation that are related to the initial PCO{sub 2} of the spring water upon discharge and the rate of CO{sub 2} degassing at each spring.

  2. Rapid supercritical CO2 fluid migration in calcite crystals at ambient conditions

    NASA Astrophysics Data System (ADS)

    Zuddas, P.; Lopez, O.; Salvi, S.

    2009-12-01

    The transport of supercritical fluids is a determining factor for several geological processes as well fundamental in predicting natural resource accumulation and distribution. Calcite, ubiquitous in geological environments may contain supercritical CO2 trapped under fluid inclusions commonly assumed to remain static under ambient conditions. Here, we report nano-meter scale observations on calcite crystal surface indicating the occurrence of fast movement of supercritical CO2 fluid inclusions hosted in the upper part of calcite crystals. Real time monitoring of calcite samples without observable presence of fluid inclusions, by in-situ Atomic Force Microscopy (AFM), shows a flat state of the calcite surface (after freshly cleaving) and the surface state condition did not change during several hours of scanning. However, AFM observations on calcite samples with visible fluid inclusions show rapid formation of nanometre-scale hillocks spontaneously formed on the surface structure of the calcite. They have an averaged height of 1 nm, and varied horizontal dimensions and geometries. The fact that hillocks formed spontaneously on flat terraces in only a few minutes, without evidence of surface dissolution, was unexpected and suggests that the source of hillock material should be derived within the crystal itself. This phenomenon was observed even changing the experimental conditions such a scan frequency of the AFM tip, environmental temperature (between 5° and 50°C) and the surface area of scanning. The observed hillocks can form by the fact that CO2-rich fluid inclusions located just under the mineral surface are at elevated internal pressure and near the rupture limit. Thus, a frail mechanical strain can case them to decrepitated and lose their fluid. Upon reaching the surface, the supercritical CO2 leaked from the fluid inclusions, mixes with the thin water layer in equilibrium with ambient CO2 partial pressure at the calcite surface, causing degassing of CO2 and facilitating calcite precipitation in the form of hillocks. We estimated CO2 supercritical fluid transport assuming a minimum depth of the fluid inclusions involved in the fluid movement and an instantaneous precipitation at the surface. We found that supercritical CO2 fluid transport in calcite is around the value of 10 nm/s. The estimated fast fluid transport rate is about 10 orders of magnitude higher than the estimated low-temperature extrapolation of solid-state diffusion vacancy in calcite crystals. Classical description of fluid transport recognises several distinct paths only for polycrystalline materials assuming the presence of inter-grain pathways as micro and nano-pore tubes. Fluid transport is usually observed in poly-phase material grains can also exhibit clear indications of multi-path migration even when visible evidence of such paths is lacking. Our study quantifies this process in the case of natural calcite at external standard conditions and be of potential importance in the artificial sequestration of CO2 under supercritical conditions.

  3. Crystallization seeds favour crystallization only during initial growth

    PubMed Central

    Allahyarov, E.; Sandomirski, K.; Egelhaaf, S.U.; Löwen, H.

    2015-01-01

    Crystallization represents the prime example of a disorder–order transition. In realistic situations, however, container walls and impurities are frequently present and hence crystallization is heterogeneously seeded. Rarely the seeds are perfectly compatible with the thermodynamically favoured crystal structure and thus induce elastic distortions, which impede further crystal growth. Here we use a colloidal model system, which not only allows us to quantitatively control the induced distortions but also to visualize and follow heterogeneous crystallization with single-particle resolution. We determine the sequence of intermediate structures by confocal microscopy and computer simulations, and develop a theoretical model that describes our findings. The crystallite first grows on the seed but then, on reaching a critical size, detaches from the seed. The detached and relaxed crystallite continues to grow, except close to the seed, which now prevents crystallization. Hence, crystallization seeds facilitate crystallization only during initial growth and then act as impurities. PMID:25975451

  4. Crystallization seeds favour crystallization only during initial growth.

    PubMed

    Allahyarov, E; Sandomirski, K; Egelhaaf, S U; Löwen, H

    2015-01-01

    Crystallization represents the prime example of a disorder-order transition. In realistic situations, however, container walls and impurities are frequently present and hence crystallization is heterogeneously seeded. Rarely the seeds are perfectly compatible with the thermodynamically favoured crystal structure and thus induce elastic distortions, which impede further crystal growth. Here we use a colloidal model system, which not only allows us to quantitatively control the induced distortions but also to visualize and follow heterogeneous crystallization with single-particle resolution. We determine the sequence of intermediate structures by confocal microscopy and computer simulations, and develop a theoretical model that describes our findings. The crystallite first grows on the seed but then, on reaching a critical size, detaches from the seed. The detached and relaxed crystallite continues to grow, except close to the seed, which now prevents crystallization. Hence, crystallization seeds facilitate crystallization only during initial growth and then act as impurities. PMID:25975451

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

    PubMed

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

    2000-12-01

    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

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

    PubMed Central

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

    2003-01-01

    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. PMID:12792020

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

    PubMed

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

    2003-06-24

    Nanobacteria-like objects evidenced at the surface of the orthopyroxenes of the Tataouine meteorite in South Tunisia have been studied by scanning and transmission electron microscopies. A method of micromanipulation has been developed to ensure that exactly the same objects were studied by both methods. We have shown that the nanobacteria-like objects are spatially correlated with filaments of microorganisms that colonized the surface of the meteoritic pyroxene during its 70 years of residence in the aridic Tataouine soil. Depressions of a few micrometers in depth are observed in the pyroxene below the carbonates, indicating preferential dissolution of the pyroxene and calcite precipitation at these locations. The nanobacteria-like small rods that constitute calcium carbonate rosettes are well crystallized calcite single crystals surrounded by a thin amorphous layer of carbonate composition that smoothes the crystal edges and induces rounded shapes. Those morphologies are unusual for calcite single crystals observed in natural samples. A survey of recent literature suggests that the intervention of organic compounds derived from biological activity is likely in their formation. PMID:12792020

  8. 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.

  9. Modification of calcite crystal growth by abalone shell proteins: an atomic force microscope study.

    PubMed

    Walters, D A; Smith, B L; Belcher, A M; Paloczi, G T; Stucky, G D; Morse, D E; Hansma, P K

    1997-03-01

    A family of soluble proteins from the shell of Haliotis rufescens was introduced over a growing calcite crystal being scanned in situ by an atomic force microscope (AFM). Atomic step edges on the crystal surface were altered in shape and speed of growth by the proteins. Proteins attached nonuniformly to the surface, indicating different interactions with crystallographically different step edges. The observed changes were consistent with the habit modification induced by this family of proteins, as previously observed by optical microscopy. To facilitate further studies in this area, AFM techniques and certain AFM imaging artifacts are discussed in detail. PMID:9138588

  10. 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.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

    Bonny, Sandy M.; Jones, Brian

    2008-01-01

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

  13. 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

  14. 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

  15. Effect of cooling mode on product crystal size in seeded batch crystallization of potassium alum

    Microsoft Academic Search

    Norihito Doki; Noriaki Kubota; Akira Sato; Masaaki Yokota

    2001-01-01

    Potassium alum was crystallized by seeding in a batch crystallizer under controlled and natural cooling modes. Regardless of the cooling mode, the product crystal size distribution (CSD) became bi-modal at low seed concentrations because of enormous secondary nucleation. The mean mass size of the product was smaller for the natural cooling mode compared to that for the controlled cooling mode

  16. Microrobotic Streak Seeding For Protein Crystal Growth CUCS04104

    E-print Network

    Microrobotic Streak Seeding For Protein Crystal Growth CUCS­041­04 Atanas Georgiev 1 Peter Allen 1 that consists of picking individual protein crystal from growth solution the purpose X­ray data collection) transferred protein solution that optimized their growth. building high­throughput protein crystal production

  17. 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.

  18. Influence of Bacillus subtilis Cell Walls and EDTA on Calcite

    E-print Network

    Long, Bernard

    to and direct attack of the calcite surface. Atomic force microscopy images of the {101h4} surface of calciteInfluence of Bacillus subtilis Cell Walls and EDTA on Calcite Dissolution Rates and Crystal Surface features on the calcite {101h4} surface. The calcite dissolution rates are compared at equivalent

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Isolation and thermal characterization of high-melting seed crystals formed during cocoa butter solidification

    Microsoft Academic Search

    Thomas R. Davis; Paul S. Dimick

    1989-01-01

    Seed crystals which formed during early stages of cocoa butter solidification have been isolated and determined to have extremely\\u000a high melting points. The melting points of the seed crystals generally exceeded 60C, in contrast to cocoa butter, which melts\\u000a between 30–35C. In addition, the melting point of the seed crystals decreased as a function of crystal growth time. Evidence\\u000a suggests

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

    NASA Astrophysics Data System (ADS)

    Ali, Imtiaj; Schneider, Phil Andrew

    2005-05-01

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

  5. Phosphates Recovery through Hydroxyapatite Crystallization from Wastewater Using Converter Slag as a Seed Crystal

    Microsoft Academic Search

    Duan Jin-ming; Cao Yin-lan; He Bi-yan

    2010-01-01

    With powdered converter slag used as a seed crystal, the effects of slag dosage, pH, temperature, and Ca2+ concentration on phosphate removal from synthetic solution through crystallization were investigated in batch experiments. The results indicated that slag concentration of 1.7 g\\/L, pH value of 9-10, reaction time of 3h , reaction temperature of 20-25°C, Ca\\/P molar ratio of 2, seemed

  6. 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.

  7. CaCO3 biomineralization: acidic 8-kDa proteins isolated from aragonitic abalone shell nacre can specifically modify calcite crystal morphology.

    PubMed

    Fu, Germaine; Valiyaveettil, Suresh; Wopenka, Brigitte; Morse, Daniel E

    2005-01-01

    Acidic proteins from many biogenic minerals are implicated in directing the formation of crystal polymorphs and morphologies. We characterize the first extremely acidic proteins purified from biomineralized aragonite. These abalone nacre proteins are two variants of 8.7 and 7.8 kDa designated AP8 (for aragonite proteins of approximately 8 kDa). The AP8 proteins have compositions dominated by Asx ( approximately 35 mol %) and Gly ( approximately 40 mol %) residues, suggesting that their structures have high Ca(2+)-binding capacity and backbone flexibility. The growth of asymmetrically rounded CaCO(3) crystals in the presence of AP8 reveals that both proteins preferentially interact with specific locations on the crystal surface. In contrast, CaCO(3) crystals grown with nacre proteins depleted of AP8 retain the morphology of unmodified calcite rhombohedra. Our observations thus identify sites of protein-mineral interaction and provide evidence to support the long-standing theory that acidic proteins are more effective crystal-modulators than other proteins from the same biomineralized material. PMID:15877344

  8. REE diffusion in calcite

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.

    1998-08-01

    Chemical diffusion of four rare-earth elements (La, Nd, Dy and Yb) has been measured in natural calcite under anhydrous conditions, using rare-earth carbonate powders as the source of diffusants. Experiments were run in sealed silica capsules along with finely ground calcite to ensure stability of the single-crystal samples during diffusion anneals. Rutherford backscattering spectroscopy (RBS) was used to measure diffusion profiles. The following Arrhenius relations were obtained over the temperature range 600-850°C: DLa =2.6×10 -14 exp(-147±14 kJ mol -1/ RT) m 2 s -1, DNd =2.4×10 -14 exp(-150±13 kJ mol -1/ RT) m 2 s -1, DDy =2.9×10 -14 exp(-145±25 kJ mol -1/ RT) m 2 s -1, DYb =3.9×10 -12 exp(-186±23 kJ mol -1/ RT) m 2 s -1. In contrast to previous findings for refractory silicates (e.g. zircon), differences in transport rates among the REE are not pronounced over the range of temperature conditions investigated in this study. Diffusion of the REE is significantly slower than diffusion of the divalent cations Sr and Pb and slower than transport of Ca and C at temperatures above ˜650°C. Fine-scale zoning and isotopic and REE chemical signatures may be retained in calcites under many conditions if diffusion is the dominant process affecting alteration.

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

    PubMed

    Yim, S; Kim, E-H

    2004-07-01

    This study was performed to select a preferred seed crystal material for the phosphorus crystallization process through a comparative study of four materials: electron arc furnace, blast furnace and converter slag, and phosphate rock. Leaching and phosphorus removal tests were conducted to evaluate the efficacy of the four materials as seeding agents. Converter slag demonstrated a much larger leaching capacity with respect to calcium and hydroxide ions than did either electron arc furnace or blast furnace slag. The average phosphorus removal efficiencies of phosphorus rock, and the electron arc furnace, blast furnace and converter slag were 35.9%, 74.2%, 99.1%, and 94.5% following 20, 17, 32, and 175 days of leach time, respectively. Consideration of both technical and cost factors suggests that converter slag may have competitive advantages over the other three seed materials. X-ray diffraction (XRD) analysis showed that peak patterns for hydroxyapatite increased slightly as the hydrous flow time was extended. Scanning electron micrograph (SEM) images revealed that finely distributed cubic crystals were deposited on the surfaces of converter slag. When analyzed by energy dispersive x-ray spectrometer (EDS) mapping, the crystals gave a composition mole ratio (Ca/P) of 1.97 and they were determined to be hydroxyapatite. PMID:15346854

  10. Microrobotic Streak Seeding For Protein Crystal Growth CUCS-041-04

    E-print Network

    Microrobotic Streak Seeding For Protein Crystal Growth CUCS-041-04 Atanas Georgiev1 , Peter K the task known as crystal mounting that consists of picking an individual protein crystal from its growth Abstract We present a microrobotic system for protein crystal micromanipulation tasks. The focus

  11. The role of silicate surfaces on calcite precipitation kinetics

    NASA Astrophysics Data System (ADS)

    Stockmann, Gabrielle J.; Wolff-Boenisch, Domenik; Bovet, Nicolas; Gislason, Sigurdur R.; Oelkers, Eric H.

    2014-06-01

    The aim of this study is to illuminate how calcite precipitation depends on the identity and structure of the growth substrate. Calcite was precipitated at 25 °C from supersaturated aqueous solutions in the presence of seeds of either calcite or one of six silicate materials: augite, enstatite, labradorite, olivine, basaltic glass and peridotite rock. Calcite saturation was achieved by mixing a CaCl2-rich aqueous solution with a NaHCO3-Na2CO3 aqueous buffer in mixed-flow reactors containing 0.5-2 g of mineral, rock, or glass seeds. This led to an inlet fluid calcite saturation index of 0.6 and a pH equal to 9.1. Although the inlet fluid composition, flow rate, and temperature were identical for all experiments, the onset of calcite precipitation depended on the identity of the seeds present in the reactor. Calcite precipitated instantaneously and at a constant rate in the presence of calcite grains. Calcite precipitated relatively rapidly on labradorite, olivine, enstatite, and peridotite (mainly composed of Mg-olivine) surfaces, but more slowly on augite and basaltic glass. Calcite precipitation rates, however, became independent of substrate identity and mass over time, and all rates approach 10-9.68 ± 0.08 mol/s for ?10 day long experiments and 10-9.21 ± 0.2 mol/s for ?70 day long experiments. Scanning Electron Microscope images showed olivine, enstatite and peridotite surfaces to be covered extensively with calcite coatings at the end of the experiments. Less calcite was found on labradorite and augite, and the least on basaltic glass. In all cases, calcite precipitation occurs on the mineral, rock or glass surfaces. Calcite precipitation on these surfaces, however, negligibly affects the dissolution rates of the silicate grains. These results support ultramafic and basalt carbonation as a long-term carbon storage strategy, as calcite readily precipitates on the surfaces of minerals contained in these rocks without inhibiting their dissolution.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

    Luo, Chuanfu; Sommer, Jens-Uwe

    2010-03-01

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

  14. Improved synthesis of fine zinc borate particles using seed crystals

    NASA Astrophysics Data System (ADS)

    Gürhan, Deniz; Çakal, Gaye Ö.; Ero?lu, ?nci; Özkar, Saim

    2009-03-01

    Zinc borate is a flame retardant additive used in polymers, wood applications and textile products. There are different types of zinc borate having different chemical compositions and structures. In this study, the production of zinc borate having the molecular formula of 2ZnO·3B 2O 3·3.5H 2O was reexamined by studying the effects of reaction parameters on the properties of product as well as the reaction kinetics. Production of zinc borate from the reaction of boric acid and zinc oxide in the presence of seed crystals was performed in a continuously stirred, temperature-controlled batch reactor having a volume of 1.5 L. Samples taken in regular time intervals during the experiments were analyzed for the concentration of zinc oxide and boron oxide in the solid as well as for the conversion of zinc oxide to zinc borate versus time. The zinc borate production reaction was fit to the logistic model. The reaction rate, reaction completion time, composition and particle size distribution of zinc borate product were determined by varying the following parameters: the boric acid to zinc oxide ratio (H 3BO 3:ZnO=3:1, 3.5:1, 5:1 and 7:1), the particle size of zinc oxide (10 and 25 ?m), stirring rate (275, 400, 800 and 1600 rpm), temperature (75, 85 and 95 °C) and the size of seed crystals (10 and 2 ?m). The products were also analyzed for particle size distribution. The experimental results showed that the reaction rate increases with the increase in H 3BO 3:ZnO ratio, particle size of zinc oxide, stirring rate and temperature. Concomitantly, the reaction completion time is decreased by increasing the H 3BO 3:ZnO ratio, stirring rate and temperature. The average particle sizes of the zinc borate products are in the range 4.3-16.6 ?m (wet dispersion analysis).

  15. 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.

  16. 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.

  17. 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.

  18. Intracrystalline deformation of calcite

    Microsoft Academic Search

    J. H. P. de Bresser

    1991-01-01

    It is well established from observations on natural calcite tectonites that\\u000aintracrystalline plastic mechanisms are important during the deformation of calcite\\u000arocks in nature. In this thesis, new data are presented on fundamental aspects of\\u000adeformation behaviour of calcite under conditions where 'dislocation creep'\\u000amechanisms dominate. The data provide a better understanding of the rheological\\u000abehaviour of calcite rocks, and

  19. 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.

  20. Hydrothermal calcite in the Elephant Moraine

    SciTech Connect

    Faure, G.; Taylor, K.S.; Jones, L.M.

    1986-01-01

    In the course of geologic mapping of the Elephant Moraine on the east antarctic ice sheet, Faure and Taylor (1985) collected several specimens of black botryoidal calcite, composed of radiating acicular crystals that resemble stromatolites. Calcite from this and other specimens is significantly enriched in strontium-87 (the strontium-87/strontium-86 ratio equals 0.71417 +/- 0.00002), carbon-12 (delta carbon-13 equals -22.9 parts per thousand, PDB standard) and oxygen-16 (delta oxygen-18 equals -21.1 parts per thousand, standard mean ocean water) compared with calcite of marine origin. The enrichment in carbon-12 is similar to that of calcite associated with coal in the Allan Hills. The enrichment in oxygen-16 indicates that the calcite from the Elephant Moraine could only have precipitated in isotopic equilibrium with glacial melt water. Therefore, the temperature at which the black calcite precipitated from water of that isotope composition was about 85/sup 0/C. A temperature of this magnitude implies that the black calcite formed as a result of volcanic activity under the east antarctic ice sheet. The enrichment of the black calcite in carbon-12 suggests that it formed in part from carbon dioxide derived from the coal seams of the Weller Formation in the Beacon Supergroup. The isotopic composition of strontium in the black calcite is similar to that of carbonate beds and concretions in the Beacon rocks of southern Victoria Land. A volcanic-hydrothermal origin is also consistent with the very low total organic carbon content of 0.15% in the calcite.

  1. 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.

  2. 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...

  3. Characterization of Semi-Insulating CdTe Crystals Grown by Horizontal Seeded Physical Vapor Transport

    NASA Technical Reports Server (NTRS)

    Chattopadhyay, K.; Feth, S.; Chen, H.; Burger, A.; Su, Ching-Hua

    1998-01-01

    CdTe crystals were grown by horizontal seeded physical vapor transport technique in uncoated and boron nitride coated fused silica ampoules with the source materials near the congruent sublimation condition. The grown crystals were characterized by current-voltage measurements, low temperature photoluminescence spectroscopy, near IR transmission optical microscopy, spark source mass spectroscopy and chemical etching. The measured resistivities of the crystals were in the high-10(exp 8) ohm-cm range. Although the crystal grown in the boron nitride coating was contaminated with boron from the photoluminescence measurements, the coating yielded a single crystal with no inclusions or precipitates.

  4. 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.

  5. 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.

  6. Hydroxyapatite crystallization from a highly concentrated phosphate solution using powdered converter slag as a seed material

    Microsoft Academic Search

    Eung-Ho Kim; Soo-Bin Yim; Ho-Chan Jung; Eok-Jae Lee

    2006-01-01

    A system for recovering phosphorus from membrane-filtrate from a sludge reduction process containing high phosphorus concentrations was developed. In this system, referred to as the completely mixed phosphorus crystallization reactor, powdered converter slag was used as a seed material. In a preliminary experiment, the optimal pH range for metastable crystallization of phosphorus from membrane-filtrate containing about 100mg\\/L PO4-P was found

  7. Molecular Structure of Calcite

    NSDL National Science Digital Library

    2002-08-14

    Calcite is an essential mineral in limestone and marble which are used in the building, steel, chemical, and glass industries. It is found in abundance on the earth. Calcite was first produced in translucent ("Iceland Spar") form in the seventeenth century for optical uses. In 1928, William Nicol used it for Polaroid Sunglasses in an effort to deflect the sunlight. Today, calcite has a large number of uses: optical and crystallography research; as a component of animal feed, antacids, statues, and dough strengthener; in the production of paper and photography; and to make mortar, cement, concrete and asphalt.

  8. PRIMARY CALCITE Cfluid << Csolid ~

    E-print Network

    Fantle, Matthew

    to foraminfer nannofossil ooze nannofossil chalk to foraminfer nannofossil chalk nannofossil chalk to foraminfer nannofossil chalk Determinng the fractionation factor between Ca in calcite and Ca in solu- tion is important

  9. Hydroxyapatite crystallization from a highly concentrated phosphate solution using powdered converter slag as a seed material.

    PubMed

    Kim, Eung-Ho; Yim, Soo-Bin; Jung, Ho-Chan; Lee, Eok-Jae

    2006-08-25

    A system for recovering phosphorus from membrane-filtrate from a sludge reduction process containing high phosphorus concentrations was developed. In this system, referred to as the completely mixed phosphorus crystallization reactor, powdered converter slag was used as a seed material. In a preliminary experiment, the optimal pH range for metastable crystallization of phosphorus from membrane-filtrate containing about 100mg/L PO(4)-P was found to be 6.6-7.0. The laboratory scale completely mixed phosphorus crystallization reactor, actually operated in pH range of 6.8-7.6 for influent 72.9 mg/L PO(4)-P, achieved an average efficiency of phosphorus removal from the membrane-filtrate of 52.4% during a 30-day experiment. Mixed-liquor suspended solids (MLSS) measurements revealed that, out of 0.24 kg PO(4)-P in the original membrane-filtrate fed into the reactor, 0.12 kg PO(4)-P was recovered on the seed particles after 30 days. X-ray diffraction (XRD) pattern and Fourier transform infrared (FT-IR) spectra of the crystalline material deposited on the seed particles showed peaks consistent with hydroxyapatite. Scanning electron micrograph (SEM) images exhibited that finely distributed crystalline material was formed on the surfaces of seed particles. Energy dispersive X-ray spectroscopy (EDS) mapping analysis revealed that the molar composition ratio of Ca/P of the crystalline material was 1.84. The Ca/P molar ratio>1.67 for crystalline substance might result from the presence of CaCO(3) on the crystalline surfaces. A particle size distribution analysis showed that the average particle size increased from 22 microm for the original converter slag seed particles, to 94 microm after 30 days of phosphorus crystallization. Collectively, the present results suggest that the proposed phosphorus crystallization recovery system is an effective tool for recycling phosphorus from phosphate solution. PMID:16504382

  10. Single crystal formation in micro/nano-confined domains by melt-mediated crystallization without seeds

    NASA Astrophysics Data System (ADS)

    Pan, Heng; Shou, Wan

    2015-06-01

    Using molecular dynamics (MD) simulation, we study the characteristics of unseeded crystallization within nano/microscale confining domains. It is demonstrated that unseeded crystallization can yield single crystal domains facilitated by the confinement effects. The stochastic nature of this process and the mechanisms leading to single crystal formation are revealed. A phenomenological model has been developed and tailored by MD simulations, which was applied to quantitatively evaluate the effects of domain size and processing laser pulse width on single crystal formation.

  11. Growth of CuCl single crystals by the top seeded solution growth method

    NASA Astrophysics Data System (ADS)

    Inoue, Tetsuo; Kuriyama, Masao; Komatsu, Hiroshi

    1991-06-01

    CuCl crystals were grown from a solution containing KCl as a flux using the top seeded solution growth method. The essential driving force for growth in this study was mass transport via the temperature gradient and the melt temperatures were kept constant during growth. This is an important distinction from the more common type of top seeded solution growth, where decreasing temperature drives the growth. The effects of the seed orientation ([100], [111] and [110]), KCl concentration (3.0-24.9 mol%) and growth rate (0.25-5.22 mm/h) upon the crystal quality were studied. The most favorable conditions were 3.0 mol% KCl and R ? 0.6 mm/h. Transparent crystals with large grain size (5-10 mm in diameter) were obtained under these conditions. The distribution of KCl inclusions and the internal strains in the crystals were also examined, using the dark-field illumination and the photo-elastic method, respectively.

  12. ?-Linolenic acid enrichment from Borago officinalis and Echium fastuosum seed oils and fatty acids by low temperature crystallization

    Microsoft Academic Search

    Juan Carlos López-Martínez; Pablo Campra-Madrid; José Luis Guil-Guerrero

    2004-01-01

    Solvent winterization of seed oil and free fatty acids (FFAs) was employed to obtain ?-linolenic acid (GLA; 18:3?6) concentrates from seed oils of two Boraginaceae species, Echium fastuosum and Borago officinalis. Different solutions of seed oils and FFAs from these two oils at 10%, 20% and 40% (w\\/w) were crystallized at 4°C, ?24°C and ?70°C, respectively, using hexane, acetone, diethyl

  13. 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

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

    Microsoft Academic Search

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

    2005-01-01

    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

  15. 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.

  16. Sorption and desorption of arsenate and arsenite on calcite

    NASA Astrophysics Data System (ADS)

    Sø, Helle U.; Postma, Dieke; Jakobsen, Rasmus; Larsen, Flemming

    2008-12-01

    The adsorption and desorption of arsenate (As(V)) and arsenite (As(III)) on calcite was investigated in a series of batch experiments in calcite-equilibrated solutions. The solutions covered a broad range of pH, alkalinity, calcium concentration and ionic strength. The initial arsenic concentrations were kept low (<33 ?M) to avoid surface precipitation. The results show that little or no arsenite sorbs on calcite within 24 h at an initial As concentration of 0.67 ?M. In contrast, arsenate sorbs readily and quickly on calcite. Likewise, desorption of arsenate from calcite is fast and complete within hours, indicating that arsenate is not readily incorporated into the calcite crystal lattice. The degree of arsenate sorption depends on the solution chemistry. Sorption increases with decreasing alkalinity, indicating a competition for sorption sites between arsenate and (bi)carbonate. pH also affects the sorption behavior, likely in response to changes in arsenate speciation or protonation/deprotonation of the adsorbing arsenate ion. Finally, sorption is influenced by the ionic strength, possibly due to electrostatic effects. The sorption of arsenate on calcite was modeled successfully using a surface complexation model comprising strong and weak sites. In the model, the adsorbing arsenate species were HAsO4- and CaHAsO40. The model was able to correctly predict the adsorption of arsenate in the wide range of calcite-equilibrated solutions used in the batch experiments and to describe the non-linear shape of the sorption isotherms. Extrapolation of the experimental results to calcite bearing aquifers suggests a large variability in the mobility of arsenic. Under reduced conditions, arsenite, which does not sorb on calcite, will dominate and, hence, As will be highly mobile. In contrast, when conditions are oxidizing, arsenate is the predominant species and, because arsenate adsorbs strongly on calcite, As mobility will be significantly retarded. The estimated retardation factors for arsenate in carbonate aquifers range from 25 to 200.

  17. 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...

  18. Demonstration of Single-Crystal Self-Seeded Two-Color X-Ray Free-Electron Lasers

    NASA Astrophysics Data System (ADS)

    Lutman, A. A.; Decker, F.-J.; Arthur, J.; Chollet, M.; Feng, Y.; Hastings, J.; Huang, Z.; Lemke, H.; Nuhn, H.-D.; Marinelli, A.; Turner, J. L.; Wakatsuki, S.; Welch, J.; Zhu, D.

    2014-12-01

    A scheme for generating two simultaneous hard-x-ray free-electron laser pulses with a controllable difference in photon energy is described and then demonstrated using the self-seeding setup at the Linac Coherent Light Source (LCLS). The scheme takes advantage of the existing LCLS equipment, which allows two independent rotations of the self-seeding diamond crystal. The two degrees of freedom are used to select two nearby crystal reflections, causing two wavelengths to be present in the forward transmitted seeding x-ray pulse. The free-electron laser system must support amplification at both desired wavelengths.

  19. Demonstration of single-crystal self-seeded two-color x-ray free-electron lasers.

    PubMed

    Lutman, A A; Decker, F-J; Arthur, J; Chollet, M; Feng, Y; Hastings, J; Huang, Z; Lemke, H; Nuhn, H-D; Marinelli, A; Turner, J L; Wakatsuki, S; Welch, J; Zhu, D

    2014-12-19

    A scheme for generating two simultaneous hard-x-ray free-electron laser pulses with a controllable difference in photon energy is described and then demonstrated using the self-seeding setup at the Linac Coherent Light Source (LCLS). The scheme takes advantage of the existing LCLS equipment, which allows two independent rotations of the self-seeding diamond crystal. The two degrees of freedom are used to select two nearby crystal reflections, causing two wavelengths to be present in the forward transmitted seeding x-ray pulse. The free-electron laser system must support amplification at both desired wavelengths. PMID:25554887

  20. Method and apparatus for inoculating crystallization seeds into a liquid latent heat storage substance

    SciTech Connect

    Lindner, F.; Scheunemann, K.

    1984-07-24

    A method and apparatus for inoculating a liquid latent heat storage substance of the type convertible to the solid state on cooling is disclosed. A portion of the substance is caused to crystallize on a cooled active surface, immersed in the substance and preferably vertically arranged, whereupon the active surface is heated to fuse-off the formed crystals to release them into the liquid portion of the storage substance to thus form inoculation seeds on which further crystallization of the storage substance takes place on withdrawal of heat from same. In one described embodiment, a pair of active surfaces is provided by using a Peltier element operating with a DC source having selectively reversible polarity whereby one surface is cooled down while the other is heated and vice versa, depending on the instant polarity of the DC source. In another embodiment, the active surface is alternately heated and cooled by heat carrier medium of a heat pump circulation system drawn from the respective sections of the system in alternating fashion. Due to the formation of crystallization seeds from the heat storage substance, problems normally associated with the use of a foreign inoculation substance are avoided.

  1. 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.

  2. 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

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

    PubMed Central

    de Almeida Gadelha, Carlos Alberto; Moreno, Frederico Bruno Mendes Batista; Santi-Gadelha, Tatiane; Cajazeiras, João Batista; da Rocha, Bruno Anderson M.; Rustiguel, Joane Kathelen Rodrigues; Freitas, Beatriz Tupinamba; Canduri, Fernanda; Delatorre, Plínio; de Azevedo, Walter Filgueira; 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?Å resolution using a synchrotron-radiation source. The ConM crystal belongs to the orthorhombic space group P21212, 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. PMID:16508099

  4. SIMULATION OF ROCKET SEEDING OF CONVECTIVE CLOUDS WITH COARSE HYGROSCOPIC AEROSOL. 1. CONDENSATION GROWTH OF CLOUD DROPLETS ON SALT CRYSTALS

    Microsoft Academic Search

    M. T. Abshaev; A. M. Abshaev; M. K. Zhekamukhov; E. I. Potapov; I. A. Garaba; E. A. Zasavitsky

    Laws of aerosol particle distribution at hygroscopic seeding of convective clouds by means of antihail rockets are considered. Influence of salt particle dispersion degree on inten- sity of condensation growth of separate cloud droplets on these particles is investigated. Ana- lytical formulae describing variation of radius of NaCl crystal and cloud droplet growing on the salt crystal until its entire

  5. 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

  6. The effect of seed crystals of hydroxyapatite and brushite on the crystallization of calcium oxalate in undiluted human urine in vitro: implications for urinary stone pathogenesis.

    PubMed Central

    Grover, Phulwinder K.; Kim, Dong-Sun; Ryall, Rosemary Lyons

    2002-01-01

    BACKGROUND: The aim of this study was to determine whether crystals of hydroxyapatite (HA) or brushite (BR) formed in urine promote the epitaxial deposition of calcium oxalate (CaOx) from undiluted human urine in vitro and thereby explain the occurrence of phosphate in the core of urinary stones consisting predominantly of CaOx. MATERIALS AND METHODS: Crystals of HA, BR, and CaOx were generated from human urine and their identity confirmed by X-ray analysis. Standard quantities of each crystal were then added to separate aliquots of pooled undiluted human urine and CaOx crystallization was induced by the addition of identical loads of sodium oxalate. Crystallization was monitored by Coulter Counter and (14) C-oxalate analysis and the precipitated crystals were examined by scanning electron microscopy. RESULTS: In comparison with the control to which no seeds were added, addition of CaOx crystals increased the deposition of (14) C-oxalate by 23%. On the other hand, seeds of HA and BR had no effect. These findings were supported by Coulter Counter analysis, which showed that the average modal sizes of crystal particles precipitated in the presence of HA and BR seeds were indistinguishable from those in the control, whereas those deposited in the presence of CaOx were significantly larger. Scanning electron microscopy confirmed these results, demonstrating that large aggregates of CaOx dihydrates were formed in the presence of CaOx seeds, whereas BR and to a lesser extent HA seeds were scattered free on the filtration membrane and attached like barnacles on the surface of the freshly precipitated CaOx crystals. CONCLUSION: Seed crystals of HA or BR do not promote CaOx deposition in urine in vitro and are therefore unlikely to influence CaOx crystal formation under physiologic conditions. However, binding of HA and BR crystals to, and their subsequent enclosure within, actively growing CaOx crystals might occur in vivo, thereby explaining the occurrence of mixed oxalate/phosphate stones. PMID:12149569

  7. Seeding Steps Droplet Location

    E-print Network

    Georgiev, Atanas

    Seeding Steps Droplet Location Sample Seeding Run Crystal Detection Design and Fabrication seeding and crystal mounting Prototype Microrobotic Streak Seeding System Robotic Protein Crystal Streak Seeding Using Silicon Microtools Atanas Georgiev1, Peter Allen1, William Edstrom2, John Hunt2, Ting Song3

  8. Stable (H, O, C) and noble-gas (He and Ar) isotopic compositions from calcite and fluorite in the Speewah Dome, Kimberley Region, Western Australia: implications for the conditions of crystallization and evidence for the influence of crustal-mantle fluid mixing

    NASA Astrophysics Data System (ADS)

    Czuppon, Gy; Ramsay, R. R.; Özgenc, I.; Demény, A.; Gwalani, L. G.; Rogers, K.; Eves, A.; Papp, L.; Palcsu, L.; Berkesi, M.; Downes, P. J.

    2014-12-01

    In this study, the C-O-isotopic data from calcite at Yungul and Wilmott (Speewah. Western-Australia) are integrated with microthermometry, H2O-, CO2-content and H-He-Ar-isotopic data from fluid inclusions in genetically related calcite and fluorite to map the origin and crystallization paths of the fluids. In addition to the hydrogen isotopic compositions of fluid inclusions in fluorite, oxygen isotopic compositions were also determined by cavity ring-down spectroscopy. The geochemical data suggest mixing of a CO2-dominated mantle fluid and a H2O-domintated crustal brine. The fluid produced by this mixing is characterized by radiogenic (crustal-like) 3He/4He ratios, crustal-like ?D values, relatively high salinity (19 - 24wt.% NaCl eq.), moderate homogenization temperatures (150 - 450 °C) and mantle-like CO2/3He ratios. Moreover, the large isotopic and elemental variations found in calcite indicate that its formation was accompanied by an extensive degassing (open system) leading to a decrease in ?D and an increase in the CO2/3He values relative to the starting fluid composition. This degassing is consistent with the fluidal- and breccia-like texture of calcite observed in the field. In contrast, the fluorite which has coarse-grained banded to vughy textures formed in a passive aqueous system. Apparently the fluid that formed the fluorite has the same origin as the calcite, but the higher water content and the more radiogenic 3He/4He ratios reflect a greater involvement of crustal fluids. The historical description of the calcite-fluorite system in the Speewah area as "carbonatite" is now considered inappropriate because there is no evidence that crystallization is dominated by magmatic processes.

  9. Sulfated Macromolecules as Templates for Calcite Nucleation and Growth

    NASA Astrophysics Data System (ADS)

    David, M.; Passalacqua, K.; Neira, A. C.; Fernandez, M. S.

    2003-12-01

    Mineralization of egg and seashells is controlled by an intimate association of inorganic materials with organic macromolecules. Among them, particular polyanionic sulfated macromolecules referred to as proteoglycans have been described to be involved in the calcification of these biominerals. The sulfated moieties of the proteoglycans are part of polymer chains constituted of building-blocks of disaccharide units, referred to as sulfated glycosaminoglycans (GAGs), which are covalently attached to a protein core. By using a sitting drop crystallization assay under controlled conditions of time, pH and reactants concentration, we have tested several sulfated and non-sulfated GAGs (i.e.: dermatan and keratan sulfate, hyaluronic acid and heparin), differing in their sulfonate and carboxylate degree and pattern, in their ability to modify calcium carbonate crystal morphology as observed under scanning electron microscopy. Without the addition of GAGs, regular \\{104\\} rhombohedral calcite crystals were obtained. When hyaluronic acid (HA), a non-sulfated but carboxylated GAG, was added, 20 mm long piles of unmodified calcite crystals were observed. When desulfated dermatan, which is an epimeric form of HA but shorter polymer, having their carboxylate groups in an inverted configuration, was added, isolated rhombohedral \\{104\\} calcite crystals showing rounded corners with planes oriented parallel to the c axis were observed. When dermatan sulfated was added, isolated calcite crystals exhibit a columnar morphology as a \\{hk0\\} cylinder with three \\{104\\} faces forming a cap at both ends. Heparin activity depends on the fraction added. Fast-moving heparin fraction (FM), is an undersulfated, low-molecular-weight heterogeneous polymer, while slow-moving heparin fraction (SM) is an high-molecular-weight homogeneous polymer rich in trisulfated-disaccharide units. When FM was added, isolated calcite crystals displayed rhombohedrical \\{104\\} faces but flat corners of \\{111\\} faces. The addition of the hypersulfated heparin SM induce the formation of large rosette-like aggregated calcite crystals, where the majority of the \\{104\\} faces appeared not to be lost, although aggregation is done by different kind of faces. It is concluded that, the variation of the sulfate and carboxylate content and configuration drastically changed the morphology of the calcite crystals. The production of calcite particles with defined morphologies could be interesting for the design of novel materials with desirable shape- and texture-depending properties. Granted by FONDAP 11980002.

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

    SciTech Connect

    Rangarajan, Erumbi S.; Izard, Tina (Scripps)

    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}.

  11. Growth rates anisotropy of synthetic quartz crystals grown on Z-cut hexagonal seeds and computer simulations of growth process

    Microsoft Academic Search

    H. Iwasaki; F. Iwasaki; V. S. Balitsky; L. V. Balitskaya; I. B. Makhina

    1998-01-01

    In quartz crystals grown on Z-cut hexagonal seeds in Na2CO3 solution, relations between specific sizes on as-grown crystal and growth rates normal to principal faces, R,r,m,Z, were formulated by two procedures; geometrical scheme on crystal form and crystal growth scheme by computer experiments. Growth rates, gr(R), gr(r), gr(m), gr(Z), were evaluated respectively to be 0.017, 0.046, 0.0016, 0.25(mm\\/d). The growth

  12. 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

  13. Computer simulation of growth process in synthetic quartz crystals grown from X-bar, Y-bar and rectangular Z-plate seeds

    Microsoft Academic Search

    H. Iwasaki; F. Iwasaki; H. Yokokawa; M. Kurashige; K. Oba

    2002-01-01

    The growth simulations of synthetic quartz crystals grown on seeds with industrialized sizes and orientations were shown on the procedure by means of the setting of virtual lengths between the seed center and principal crystal faces to be grown. The virtual lengths needed for simulations are calculated on the given sizes and shapes of seeds, X-bar, Y-bar and rectangular Z-plate.

  14. CaCO 3 Biomineralization:  Acidic 8-kDa Proteins Isolated from Aragonitic Abalone Shell Nacre Can Specifically Modify Calcite Crystal Morphology

    Microsoft Academic Search

    Germaine Fu; Suresh Valiyaveettil; Brigitte Wopenka; Daniel E. Morse

    2005-01-01

    Acidic proteins from many biogenic minerals are implicated in directing the formation of crystal polymorphs and morphologies. We characterize the first extremely acidic proteins purified from biomineralized aragonite. These abalone nacre proteins are two variants of 8.7 and 7.8 kDa designated AP8 (for aragonite proteins of approximately 8 kDa). The AP8 proteins have compositions dominated by Asx (35 mol %)

  15. 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

  16. The growth, morphology and perfection of fluoranthene crystals grown from supercooled chlorine derivative solutions on spontaneously formed seeds

    NASA Astrophysics Data System (ADS)

    Marciniak, B.

    2002-03-01

    Crystals of the aromatic hydrocarbon fluoranthene have been grown from supercooled solutions, employing five chlorinated hydrocarbons as solvents, on spontaneously formed seeds under conditions of constant temperature growth. Total impurity content in the material used for growth determined by GC-FID and GC-MS methods was ?10 -3 mass%. All the crystals grown possessed only columnar habit exhibiting simultaneously significant differences in the growth forms, mainly according to the solvent. The largest crystals of 50×12×5 mm 3 dimensions, exhibiting six forms, were grown from the nearest to ideal solution in trichloroethylene. Based on the measured solubility data, the activity coefficient and the dissolution enthalpy of fluoranthene were evaluated at the growth temperature of the crystals and used to interpret an observed solvent effect on their morphology and structural quality. Finally, the perfection of the crystals was examined using X-ray topography and the main growth-induced defects were identified as inclusions.

  17. 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.

  18. 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.

  19. Rapid Migration of CO2 Supercritical Fluids in Calcite Cristals

    NASA Astrophysics Data System (ADS)

    Zuddas, P.; Lopez, O.; Salvi, S.; Earth Sciences Umr5123

    2010-12-01

    The transport of supercritical fluids is a determining factor for several geological processes as well fundamental in predicting natural resource accumulation and distribution. Calcite, ubiquitous in geological environments may contain supercritical CO2 trapped under fluid inclusions commonly assumed to remain static under ambient conditions. Here, we report nano-meter scale observations on calcite crystal surface indicating the occurrence of fast movement of supercritical CO2 fluid inclusions hosted in the upper part of calcite crystals. Real time monitoring of calcite samples without observable presence of fluid inclusions, by in-situ Atomic Force Microscopy (AFM), shows a flat state of the calcite surface (after freshly cleaving) and the surface state condition did not change during several hours of scanning. However, AFM observations on calcite samples with visible fluid inclusions show rapid formation of nanometre-scale hillocks spontaneously formed on the surface structure of the calcite. They have an averaged height of 1 nm, and varied horizontal dimensions and geometries. The fact that hillocks formed spontaneously on flat terraces in only a few minutes, without evidence of surface dissolution, was unexpected and suggests that the source of hillock material should be derived within the crystal itself. This phenomenon was observed even changing the experimental conditions such a scan frequency of the AFM tip, environmental temperature (between 5° and 50°C) and the surface area of scanning. The observed hillocks can form by the fact that CO2-rich fluid inclusions located just under the mineral surface are at elevated internal pressure and near the rupture limit. Thus, a frail mechanical strain can case them to decrepitated and lose their fluid. Upon reaching the surface, the supercritical CO2 leaked from the fluid inclusions, mixes with the thin water layer in equilibrium with ambient CO2 partial pressure at the calcite surface, causing degassing of CO2 and facilitating calcite precipitation in the form of hillocks. We estimated CO2 supercritical fluid transport assuming a minimum depth of the fluid inclusions involved in the fluid movement and an instantaneous precipitation at the surface. We found that supercritical CO2 fluid transport in calcite is around the value of 10nm/s. The estimated fast fluid transport rate is about 10 orders of magnitude higher than the estimated low-temperature extrapolation of solid-state diffusion vacancy in calcite crystals. Classical description of fluid transport recognises several distinct paths only for polycrystalline materials assuming the presence of inter-grain pathways as micro and nano-pore tubes. Fluid transport is usually observed in poly-phase material grains can also exhibit clear indications of multi-path migration even when visible evidence of such paths is lacking. Our study quantifies this process in the case of natural calcite at external standard conditions and be of potential importance in movement of CO2 rich fluids under supercritical conditions.

  20. 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.

  1. Effects of self-seeding and crystal post-selection on the quality of Monte Carlo-integrated SFX data.

    PubMed

    Barends, Thomas; White, Thomas A; Barty, Anton; Foucar, Lutz; Messerschmidt, Marc; Alonso-Mori, Roberto; Botha, Sabine; Chapman, Henry; Doak, R Bruce; Galli, Lorenzo; Gati, Cornelius; Gutmann, Matthias; Koglin, Jason; Markvardsen, Anders; Nass, Karol; Oberthur, Dominik; Shoeman, Robert L; Schlichting, Ilme; Boutet, Sébastien

    2015-05-01

    Serial femtosecond crystallography (SFX) is an emerging method for data collection at free-electron lasers (FELs) in which single diffraction snapshots are taken from a large number of crystals. The partial intensities collected in this way are then combined in a scheme called Monte Carlo integration, which provides the full diffraction intensities. However, apart from having to perform this merging, the Monte Carlo integration must also average out all variations in crystal quality, crystal size, X-ray beam properties and other factors, necessitating data collection from thousands of crystals. Because the pulses provided by FELs running in the typical self-amplified spontaneous emission (SASE) mode of operation have very irregular, spiky spectra that vary strongly from pulse to pulse, it has been suggested that this is an important source of variation contributing to inaccuracies in the intensities, and that, by using monochromatic pulses produced through a process called self-seeding, fewer images might be needed for Monte Carlo integration to converge, resulting in more accurate data. This paper reports the results of two experiments performed at the Linac Coherent Light Source in which data collected in both SASE and self-seeded mode were compared. Importantly, no improvement attributable to the use of self-seeding was detected. In addition, other possible sources of variation that affect SFX data quality were investigated, such as crystal-to-crystal variations reflected in the unit-cell parameters; however, these factors were found to have no influence on data quality either. Possibly, there is another source of variation as yet undetected that affects SFX data quality much more than any of the factors investigated here. PMID:25931080

  2. Gamma-linolenic acid enrichment from Borago officinalis and Echium fastuosum seed oils and fatty acids by low temperature crystallization.

    PubMed

    López-Martínez, Juan Carlos; Campra-Madrid, Pablo; Guil-Guerrero, José Luis

    2004-01-01

    Solvent winterization of seed oil and free fatty acids (FFAs) was employed to obtain gamma-linolenic acid (GLA; 18:3omega6) concentrates from seed oils of two Boraginaceae species, Echium fastuosum and Borago officinalis. Different solutions of seed oils and FFAs from these two oils at 10%, 20% and 40% (w/w) were crystallized at 4 degrees C, -24 degrees C and -70 degrees C, respectively, using hexane, acetone, diethyl ether, isobutanol and ethanol as solvents. Best results were obtained for B. officinalis FFAs in hexane, reaching a maximum GLA concentration of 58.8% in the liquid fraction (LF). In E. fastuosum, the highest GLA concentration (39.9%) was also achieved with FFAs in hexane. PMID:16233632

  3. An approach for phosphate removal with quartz sand, ceramsite, blast furnace slag and steel slag as seed crystal.

    PubMed

    Qiu, Liping; Wang, Guangwei; Zhang, Shoubin; Yang, Zhongxi; Li, Yanbo

    2012-01-01

    The phosphate removal abilities and crystallization performance of quartz sand, ceramsite, blast furnace slag and steel slag were investigated. The residual phosphate concentrations in the reaction solutions were not changed by addition of the ceramsite, quartz sand and blast furnace slag. The steel slag could provide alkalinity and Ca(2+) to the reaction solution due to its hydration activity, and performed a better phosphate removal performance than the other three. Under the conditions of Ca/P 2.0, pH 8.5 and 10 mg P/L, the phosphate crystallization occurred during 12 h. The quartz sand and ceramsite did not improve the phosphate crystallization, but steel slag was an effective seed crystal. The phosphate concentration decreased drastically after 12 h after addition of steel slag, and near complete removal was achieved after 48 h. The XRD analysis showed that the main crystallization products were hydroxyapatite (HAP) and the crystallinity increased with the reaction time. Phosphate was successfully recovered from low phosphate concentration wastewater using steel slag as seed material. PMID:22378001

  4. 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.

  5. 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

  6. Studies on shell formation. VIII. Electron microscopy of crystal growth of the nacreous layer of the oyster Crassostrea virginica.

    PubMed

    WATABE, N; SHARP, D G; WILBUR, K M

    1958-05-25

    Electron microscope observations have been made by means of the replica method on growth processes of calcite crystals of the nacreous layer of the shell of the oyster, Crassostrea virginica. Layer formation is initiated by the secretion of a conchiolin matrix and the deposition of rounded crystal seeds on or in this material. In some areas crystal seeds are elongate and within a given area show a similar orientation, probably due to slower deposition. The seeds appear to increase in size by dendritic growth, and smaller seeds become incorporated into larger ones which come into contact to form a single layer. With further growth, crystals overlap, forming a step-like arrangement. The direction of growth is frequently different in neighboring regions. Crystal seeds deposited on crystal surfaces are usually elongate and oriented. Well developed crystals have a tabular idiomorphic form and are parallel in their growth. Rounded and irregular crystals were also observed. The crystals show reticular structure with units of the order of 100 A and striations corresponding with the rhombohedral axes of the crystals. The role of the mantle is discussed in relation to the growth patterns of crystals and shell structure. PMID:13549499

  7. Capillary-Seeding Crystallization and Preliminary Crystallographic Analysis of a Solvent-Tolerant Elastase from Pseudomonas aeruginosa Strain K

    PubMed Central

    Ali, Mohd Shukuri Mohamad; Said, Zatty Syamimi @ Adura Mat; Raja Abd Rahman, Raja Noor Zaliha; Thean Chor, Adam Leow; Basri, Mahiran; Salleh, Abu Bakar

    2013-01-01

    Seeding is a versatile method for optimizing crystal growth. Coupling this technique with capillary counter diffusion crystallization enhances the size and diffraction quality of the crystals. In this article, crystals for organic solvent-tolerant recombinant elastase strain K were successfully produced through microseeding with capillary counter-diffusion crystallization. This technique improved the nucleation success rate with a low protein concentration (3.00 mg/mL). The crystal was grown in 1 M ammonium phosphate monobasic and 0.1 M sodium citrate tribasic dihydrate pH 5.6. The optimized crystal size was 1 × 0.1 × 0.05 mm3. Elastase strain K successfully diffracted up to 1.39 Å at SPring-8, Japan, using synchrotron radiation for preliminary data diffraction analysis. The space group was determined to be monoclinic space group P1211 with unit cell parameters of a = 38.99 ?, b = 90.173 Å and c = 40.60 Å. PMID:23989606

  8. 4, 961991, 2007 foraminiferal calcite

    E-print Network

    Paris-Sud XI, Université de

    available for copper. Since par- tition coefficients are usually a function of multiple factors (seawaterBGD 4, 961­991, 2007 Copper in foraminiferal calcite L. J. de Nooijer et al. Title Page Abstract/961/2007/ © Author(s) 2007. This work is licensed under a Creative Commons License. Biogeosciences Discussions

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

    SciTech Connect

    Jones, B. [Univ. of Alberta, Edmonton, Alberta (Canada). Dept. of Geology; Renaut, R.W. [Univ. of Saskatchewan, Saskatoon (Canada). Dept. of Geological Sciences

    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. Paleotransport of lanthanides and strontium recorded in calcite compositions from tuffs at Yucca Mountain, Nevada, USA

    NASA Astrophysics Data System (ADS)

    Vaniman, David T.; Chipera, Steve J.

    1996-11-01

    Secondary calcite occurs in both saturated and unsaturated hydrologic zones (SZ and UZ, respectively) in the tuffs at Yucca Mountain, Nevada, USA. In the upper UZ, the major constituents of the calcite crystal structure (C, O) have surface origins. At greater depth there is a “barren zone,” straddling the water table, where calcite is rare and mixing of surface and subsurface sources may occur. Deep in the SZ, distinctive Mn calcites reflect deep sources, including Ca released as analcime or albite formed and carbonates derived from underlying Paleozoic rocks. In the UZ and in the barren zone, above the deep Mn calcites, variations in calcite lanthanide chemistry can be used to distinguish rhyolitic from quartz-latitic sources. Lanthanide ratios and Sr contents of calcites record the chemical evolution of waters flowing through the UZ and upper SZ. Variations in calcite chemistry in the UZ and in the barren zone show that (1) Sr, which is readily exchanged with clays or zeolites, is essentially removed from some flowpaths that are in contact with these minerals and (2) traces of Mn oxides found in the tuffs have a significant effect on groundwater chemistry in the UZ and in the barren zone by removing almost all Ce from solution (evidenced by characteristic Ce depletions in calcite throughout this zone). Extreme Ce removal may be a result of Ce oxidation (Ce 3+? Ce 4+) at the surfaces of some Mn oxides, particularly rancieite. Higher Sr contents and lack of Ce depletions in the deeper Mn calcites reflect different ages, origins, and transport systems. The calcite record of lanthanide and Sr transport in the UZ shows that minor minerals (clays and zeolites) and even trace minerals (Mn oxides) will affect the compositions of groundwaters that flow over distances greater than a few tens of meters.

  11. Rate-controlled calcium isotope fractionation in synthetic calcite

    Microsoft Academic Search

    D. Lemarchand; G. J. Wasserburg; D. A. Papanastassiou

    2004-01-01

    The isotopic composition of Ca (?44Ca\\/40Ca) in calcite crystals has been determined relative to that in the parent solutions by TIMS using a double spike. Solutions were exposed to an atmosphere of NH3 and CO2, provided by the decomposition of (NH4)2CO3, following the procedure developed by previous workers. Alkalinity, pH and concentrations of CO32?, HCO3?, and CO2 in solution were

  12. Rate-controlled calcium isotope fractionation in synthetic calcite

    Microsoft Academic Search

    D. Lemarchand; G. J. Wasserburg; D. A. Papanastassiou

    2004-01-01

    The isotopic composition of Ca (Delta44Ca\\/40Ca) in calcite crystals has been determined relative to that in the parent solutions by TIMS using a double spike. Solutions were exposed to an atmosphere of NH3 and CO2, provided by the decomposition of (NH4)2CO3, following the procedure developed by previous workers. Alkalinity, pH and concentrations of CO32-, HCO3-, and CO2 in solution were

  13. Seeded growth of AlN bulk crystals in m-and c-orientation , R. Collazo a,, R.F. Dalmau b

    E-print Network

    Dietz, Nikolaus

    Seeded growth of AlN bulk crystals in m- and c-orientation P. Lu a , R. Collazo a,Ã, R.F. Dalmau b has been made in bulk crystal growth of AlN, and limited quantities of primarily c-plane (0 0 01 of these epilayers was inferior to those grown in polar (0 0 01) directions. Most of the AlN bulk crystal growth has

  14. Bioremediation of Cd by microbially induced calcite precipitation.

    PubMed

    Kang, Chang-Ho; Han, Sang-Hyun; Shin, Yujin; Oh, Soo Ji; So, Jae-Seong

    2014-03-01

    Contamination by Cd is a significant environmental problem. Therefore, we examined Cd removal from an environmental perspective. Ureolysis-driven calcium carbonate precipitation has been proposed for use in geotechnical engineering for soil remediation applications. In this study, 55 calcite-forming bacterial strains were newly isolated from various environments. Biomineralization of Cd by calcite-forming bacteria was investigated in laboratory-scale experiments. A simple method was developed to determine the effectiveness of microbially induced calcite precipitation (MICP). Using this method, we determined the effectiveness of biomineralization for retarding the flow of crystal violet through a 25-mL column. When the selected bacteria were analyzed using an inductively coupled plasma optical emission spectrometer, high removal rates (99.95%) of Cd were observed following incubation for 48 h. Samples of solids that formed in the reaction vessels were examined using a scanning electron microscope. The CdCO3 compounds primarily showed a spherical shape. The results of this study demonstrate that MICP-based sequestration of soluble heavy metals via coprecipitation with calcite may be useful for toxic heavy metal bioremediation. PMID:24458656

  15. Bioremediation of Cd by microbially induced calcite precipitation.

    PubMed

    Kang, Chang-Ho; Han, Sang-Hyun; Shin, Yujin; Oh, Soo Ji; So, Jae-Seong

    2014-02-01

    Contamination by Cd is a significant environmental problem. Therefore, we examined Cd removal from an environmental perspective. Ureolysis-driven calcium carbonate precipitation has been proposed for use in geotechnical engineering for soil remediation applications. In this study, 55 calcite-forming bacterial strains were newly isolated from various environments. Biomineralization of Cd by calcite-forming bacteria was investigated in laboratory-scale experiments. A simple method was developed to determine the effectiveness of microbially induced calcite precipitation (MICP). Using this method, we determined the effectiveness of biomineralization for retarding the flow of crystal violet through a 25-mL column. When the selected bacteria were analyzed using an inductively coupled plasma optical emission spectrometer, high removal rates (99.95 %) of Cd were observed following incubation for 48 h. Samples of solids that formed in the reaction vessels were examined using a scanning electron microscope. The CdCO3 compounds primarily showed a spherical shape. The results of this study demonstrate that MICP-based sequestration of soluble heavy metals via coprecipitation with calcite may be useful for toxic heavy metal bioremediation. PMID:24293312

  16. Controlling the morphology, composition and crystal structure in gold-seeded GaAs1-xSbx nanowires

    NASA Astrophysics Data System (ADS)

    Yuan, Xiaoming; Caroff, Philippe; Wong-Leung, Jennifer; Tan, Hark Hoe; Jagadish, Chennupati

    2015-03-01

    While III-V binary nanowires are now well controlled and their growth mechanisms reasonably well understood, growing ternary nanowires, including controlling their morphology, composition and crystal structure remains a challenge. However, understanding and control of ternary alloys is of fundamental interest and critical to enable a new class of nanowire devices. Here, we report on the progress in understanding the complex growth behaviour of gold-seeded GaAs1-xSbx nanowires grown by metalorganic vapour phase epitaxy. The competition between As and Sb atoms for incorporation into the growing crystal leads to a tunability of the Sb content over a broad range (x varies from 0.09 to 0.6), solely by changing the AsH3 flow. In contrast, changing TMSb flow is more effective in affecting the morphology and crystal structure of the nanowires. Inclined faults are found in some of these nanowires and directly related to the kinking of the nanowires and controlled by TMSb flow. Combined with the observed sharp increase of wetting angle between the Au seed and nanowire, the formation of inclined faults are attributed to the Au seed being dislodged from the growth front to wet the sidewalls of the nanowires, and are related to the surfactant role of Sb. The insights provided by this study should benefit future device applications relying on taper- and twin-free ternary antimonide III-V nanowire alloys and their heterostructures.While III-V binary nanowires are now well controlled and their growth mechanisms reasonably well understood, growing ternary nanowires, including controlling their morphology, composition and crystal structure remains a challenge. However, understanding and control of ternary alloys is of fundamental interest and critical to enable a new class of nanowire devices. Here, we report on the progress in understanding the complex growth behaviour of gold-seeded GaAs1-xSbx nanowires grown by metalorganic vapour phase epitaxy. The competition between As and Sb atoms for incorporation into the growing crystal leads to a tunability of the Sb content over a broad range (x varies from 0.09 to 0.6), solely by changing the AsH3 flow. In contrast, changing TMSb flow is more effective in affecting the morphology and crystal structure of the nanowires. Inclined faults are found in some of these nanowires and directly related to the kinking of the nanowires and controlled by TMSb flow. Combined with the observed sharp increase of wetting angle between the Au seed and nanowire, the formation of inclined faults are attributed to the Au seed being dislodged from the growth front to wet the sidewalls of the nanowires, and are related to the surfactant role of Sb. The insights provided by this study should benefit future device applications relying on taper- and twin-free ternary antimonide III-V nanowire alloys and their heterostructures. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr06307d

  17. In-situ observation of ettringite crystals

    NASA Astrophysics Data System (ADS)

    Komatsu, Ryuichi; Mizukoshi, Norihiro; Makida, Koji; Tsukamoto, Katsuo

    2009-01-01

    In-situ observation of growing ettringite crystals in solution has been carried out and the morphology change of ettringite has been investigated under various conditions. In particular, the acceleration behavior of ettringite growth in the presence of calcite, the cause of which is not yet understood, is examined. Spherulite with calcite in its core is formed first followed by the generation of acicular crystals. Compared with the in-situ observation result of crystal growth in a solution with no calcite, the effect of added calcite can be explained as a decrease in the activation energy of nucleation for ettringite around calcite.

  18. 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.

  19. The energetics of nanophase calcite

    Microsoft Academic Search

    Tori Z. Forbes; A. V. Radha; Alexandra Navrotsky

    Calcium carbonate (CaCO3) is an important component of the near-surface environment. Understanding the nature of its precipitation is important for a variety of environmental processes, as well as for the geologic sequestration of anthropogenic carbon dioxide. Calcite is the most thermodynamically stable bulk polymorph, but energy crossovers may exist that could favor the precipitation of vaterite or aragonite with decreasing

  20. Crystallization and preliminary X-ray diffraction analysis of a galactose-specific lectin from the seeds of Butea monosperma

    PubMed Central

    Abhilash, Joseph; Geethanandan, K.; Bharath, S. R.; Sadasivan, C.; Haridas, M.

    2011-01-01

    The galactose-specific lectin from the seeds of Butea monosperma has been crystallized by the hanging-drop vapour-diffusion technique. The crystals belonged to space group P1, with unit-cell parameters a = 78.45, b = 78.91, c = 101.85?Å, ? = 74.30, ? = 76.65, ? = 86.88°. X-ray diffraction data were collected to a resolution of 2.44?Å under cryoconditions (100?K) using a MAR image-plate detector system mounted on a rotating-anode X-ray generator. Molecular-replacement calculations carried out using the coordinates of several structures of legume lectins as search models indicate that the galactose-specific lectin from B. monosperma forms an octamer. PMID:21505258

  1. Crystallization and preliminary X-ray studies of a galactose-specific lectin from the seeds of Spatholobus parviflorus

    PubMed Central

    Geethanandan, K.; Abhilash, Joseph; Bharath, S. R.; Sadasivan, C.; Haridas, M.

    2011-01-01

    A galactose-specific seed lectin was purified from the legume Spatholobus parviflorus and crystallized using the hanging-drop vapour-diffusion technique. The crystals belonged to space group P1, with unit-cell parameters a = 60.998, b = 60.792, c = 78.179?Å, ? = 101.32, ? = 91.38, ? = 104.32°. X-ray diffraction data were collected under cryoconditions (100?K) to a resolution of 2.04?Å using a MAR image-plate detector system mounted on a rotating-anode X-ray (Cu?K?) generator. Molecular replacement using legume-lectin coordinates as a search model gave a tetrameric structure. PMID:21636916

  2. Alternative origins for nannobacteria-like objects in calcite

    NASA Astrophysics Data System (ADS)

    Kirkland, Brenda L.; Lynch, F. Leo; Rahnis, Michael A.; Folk, Robert L.; Molineux, Ian J.; McLean, Robert J. C.

    1999-04-01

    More than 40 calcite-precipitation experiments were performed under sterile conditions in order to investigate the origins of 25 300 nm spherical-, rod-, and ovoid-shaped objects that have been widely interpreted as evidence of nanometer-scale life (i.e., nannobacteria). Individual experiments included the addition of soluble organic compounds, common species of eubacteria, or phage-induced eubacterial lysates. These experiments indicate that many of the nanometer-scale objects have inorganic or nonnannobacterial origins. In the precipitation experiments, calcite formed euhedral crystals 50 800 nm in diameter and smaller (<50 nm) anhedral or rounded particles or protocrystals. The small anhedral or rounded solids resembled nannobacteria. The relative amount of anhedral or rounded calcite was greatest in experiments with a dissolved organic component. These controlled experiments are in accord with observations that rounded nanometer-scale objects are more common in minerals formed in organic-rich environments. Bacterial fragments occur as rounded to irregularly shaped particles that included cell-wall fragments, expulsed cytoplasm, and relict capsules that also closely resembled nannobacteria. Acid etching of the large euhedral crystals produced in the precipitation experiments also resulted in the formation of nanometer-scale features that resembled nannobacteria in natural carbonates. The shapes of the etching artifacts vary as a function of the strength of the acid and the duration of etching. Much caution is advisable in interpreting the origin of rounded features <50 nm.

  3. Controls of carbonate mineralogy and solid-solution of Mg in calcite: evidence from spelean systems

    SciTech Connect

    Gonzalez, L.A.; Lohmann, K.C.

    1985-01-01

    Precipitation of carbonate minerals in spelean systems occurs under a wide range of fluid chemistry, Mg-Ca ratios, alkalinities, pH and temperatures; thus, spelean systems provide ideal settings to determine factors controlling the mineralogy of precipitated carbonates and solid-solution of Mg in calcite. Cave waters and actively-precipitating carbonate speleothems were collected from Carlsbad Caverns National Park, New Mexico and the Mammoth-Flint Cave System, Kentucky. Carbonate mineralogy of precipitated phases was determined by x-ray diffraction, and major and minor element composition of waters and accompanying minerals were determined by Atomic Absorption Spectrophotometry. Results demonstrate that at a constant CO3 concentration the precipitation threshold for calcite to aragonite is controlled dominantly by the Mg/Ca ratio of the ambient fluid. Aragonite precipitation is favored by high Mg/Ca ratios. Conversely, with increasing CO3 concentration at constant fluid Mg/Ca ratios, calcite is preferentially precipitated. Solid-solution of Mg in calcite is positively correlated with both increased Mg/Ca ratios and CO3 concentrations. These data suggest that Mg contents of calcite can not be defined solely in terms of a homogeneous distribution coefficient. Rather, Mg concentrations can be also be affected by the CO3 concentration and degree of calcite saturation, suggesting that the rate of crystal growth also plays and important role in Mg solid-solution in calcites.

  4. Expression, purification and preliminary crystallization of amaranth 11S proglobulin seed storage protein from Amaranthus hypochondriacus L.

    PubMed Central

    Tandang-Silvas, Mary Rose; Carrazco-Peña, Laura; Barba de la Rosa, Ana Paulina; Osuna-Castro, Juan Alberto; Utsumi, Shigeru; Mikami, Bunzo; Maruyama, Nobuyuki

    2010-01-01

    11S globulin is one of the major seed storage proteins in amaranth. Recombinant protein was produced as up to ?80% of the total bacterial protein using Escherichia coli Rosetta-gami (DE3) containing pET21d with amaranth 11S globulin cDNA. The best expression condition was at 302?K for 20?h using LB medium containing 0.5?M NaCl. The recombinant protein was easily separated from most of the Escherichia coli proteins by precipitation with 0–40% ammonium sulfate solution. It formed aggregates at low temperature and at low salt concentrations. This behaviour may imply that it has a more hydrophobic nature than other 11S seed globulins. The crystals diffracted to 6?Å resolution and belonged to space group P63, with unit-cell parameters a = b = 97.6, c = 74.8?Å, ? = 120.0°. One subunit of a trimer was estimated to be present in the asymmetric unit, assuming a V sol of 41%. To obtain the complete structure solution, experiments to improve crystallization and flash-cooling conditions are in progress. PMID:20693668

  5. 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.

  6. Self-Assembly of Protein Nanofibrils Orchestrates Calcite Step Movement through Selective Nonchiral Interactions.

    PubMed

    So, Christopher R; Liu, Jinny; Fears, Kenan P; Leary, Dagmar H; Golden, Joel P; Wahl, Kathryn J

    2015-06-23

    The recognition of atomically distinct surface features by adsorbed biomolecules is central to the formation of surface-templated peptide or protein nanostructures. On mineral surfaces such as calcite, biomolecular recognition of, and self-assembly on, distinct atomic kinks and steps could additionally orchestrate changes to the overall shape and symmetry of a bulk crystal. In this work, we show through in situ atomic force microscopy (AFM) experiments that an acidic 20 kDa cement protein from the barnacle Megabalanus rosa (MRCP20) binds specifically to step edge atoms on {101?4} calcite surfaces, remains bound and further assembles over time to form one-dimensional nanofibrils. Protein nanofibrils are continuous and organized at the nanoscale, exhibiting striations with a period of ca. 45 nm. These fibrils, templated by surface steps of a preferred geometry, in turn selectively dissolve underlying calcite features displaying the same atomic arrangement. To demonstrate this, we expose the protein solution to bare and fibril-associated rhombohedral etch pits to reveal that nanofibrils accelerate only the movement of fibril-forming steps when compared to undecorated steps exposed to the same solution conditions. Calcite mineralized in the presence of MRCP20 results in asymmetric crystals defined by frustrated faces with shared mirror symmetry, suggesting a similar step-selective behavior by MRCP20 in crystal growth. As shown here, selective surface interactions with step edge atoms lead to a cooperative regime of calcite modification, where templated long-range protein nanostructures shape crystals. PMID:25970003

  7. (U-Th)/He dating and He diffusion in calcite from veins and breccia

    NASA Astrophysics Data System (ADS)

    Gautheron, C.; Cros, A.; Pagel, M.; Berthet, P.; Tassan-Got, L.; Douville, E.; Pinna-Jamme, R.; Sarda, P.

    2013-12-01

    Knowledge of He retention in crystalline calcite is mandatory to estimate the possibility of (U-Th)/He dating of calcite. To this aim, fault-filling calcite crystals from the Eocene/Oligocene Gondrecourt graben, Paris Basin, Eastern France, have been sampled, based on their relatively old, Eocene-Oligocene, precipitation age and cold thermal history (<40°C since precipitation). The samples were sorted into three main tectonic and morphological groups, including successively (1) micro-fracture calcites, (2) breccia and associated geodic calcites, and (3) vein and associated geodic calcites. (U-Th)/He dating of 63 calcite fragments yields ages dispersed from 0.2×0.02 to 35.8×2.7 Ma, as well as two older dates of 117×10 and 205×28 Ma (1s). These He ages correlate to grain chemistry, such as to Sr and ?REE concentrations or (La/Yb)N ratios, and these correlations probably reflect the evolution of parent fluid. Only the oldest He ages are in agreement with the He-retentive character of calcite as determined by Copeland et al. (2007), and these ages were obtained for the most recently precipitated crystals. To better understand the large He-age scatter and why calcites precipitated earlier show younger ages, He diffusion experiments have been conducted on 10 Gondrecourt calcite fragments from 3 samples with He ages of 0.2 to 6 Ma. In addition, a crystallographic investigation by X-Ray Diffraction (XRD) performed on similar samples reveals that the crystal structure evolves with increasing temperature, showing with micro-cracks and cleavage opening. These XRD results indicate that, in fault-filling calcite, He retention is controlled by multiple diffusion domains (MDD, Lovera et al., 1991) with various sizes, and therefore, evolves through time with strong consequences on (U-Th)/He age. We thus interpret the Gondrecourt calcite (U-Th)/He age scatter of older samples as a consequence of cleavage opening due to a succession of calcite crystallization phases related to the deformation history. Finally, we propose that the crystallization age of a calcite crystal with a known thermal history can nevertheless be retrieved by the (U-Th)/He method provided the He diffusion pattern can be measured by careful step-heating degassing analysis. Copeland, P., Watson, E.B., Urizar, S.C., Patterson, D., Lapen, T.J., 2007. Alpha thermochronology of carbonates. Geochim. Cosmochim. Acta, 71: 4488-4511. Cros, A. Gautheron, C., Pagel, M., Berthet, P., Tassan-Got, L., Douville, E., Pinna-Jamme, R., Sarda, P., submitted GCA, He behavior in calcite filling viewed by (U-Th)/He dating, He diffusion and crystallographic studies. Lovera, O.M., Richter, F.M., Harrison, T.M., 1991. Diffusion domains determined by 39Ar released during step heating. Journal of Geophysical Research, 96: 2057-2069.

  8. Calcium isotope fractionation in calcite and aragonite

    Microsoft Academic Search

    Nikolaus Gussone; Florian Böhm; Anton Eisenhauer; Martin Dietzel; Alexander Heuser; Barbara M. A. Teichert; Joachim Reitner; Gert Wörheide; Wolf-Christian Dullo

    2005-01-01

    Calcium isotope fractionation was measured on skeletal aragonite and calcite from different marine biota and on inorganic calcite. Precipitation temperatures ranged from 0 to 28°C. Calcium isotope fractionation shows a temperature dependence in accordance with previous observations: 1000·ln(?cc) = ?1.4 + 0.021·T (°C) for calcite and 1000·ln(?ar) = ?1.9 + 0.017·T (°C) for aragonite. Within uncertainty the temperature slopes are

  9. Infiltration growth of Mg-doped Nd-Ba-Cu-O seed crystals for the fabrication of large grain RE-Ba-Cu-O bulk superconductors

    NASA Astrophysics Data System (ADS)

    Li, Guo-Zheng; Li, De-Jun; Deng, Xiang-Yun; Deng, Jian-Hua; Yang, Wan-Min

    2013-05-01

    By employing the infiltration growth (IG) technique, Mg-doped Nd-Ba-Cu-O (NdBCO) seed crystals were successfully prepared through 1 wt% MgO addition both to a Nd4Ba2Cu2O10 (Nd-422) precursor powder and to a liquid source with the composition Nd2O3:CuO:BaCuO2 = 1:6:10. Differential thermal analysis (DTA) results showed that the decomposition temperature of the processed Mg-doped NdBCO crystals increased by about 20?°C compared with the general, Mg-free NdBCO seeds, thus they can be used as generic seed crystals to induce the growth of any RE-Ba-Cu-O (REBCO) single grain. This result is consistent with that observed in melt growth (MG) processed Mg-doped NdBCO crystals. Finally, highly c-axis oriented Gd-Ba-Cu-O (GdBCO) and Y-Ba-Cu-O (YBCO) large grains were successfully grown using the produced seed crystals.

  10. Sr / Mg ratios of modern marine calcite: Empirical indicators of ocean chemistry and precipitation rate

    NASA Astrophysics Data System (ADS)

    Carpenter, Scott J.; Lohmann, Kyger C.

    1992-05-01

    Holocene biotic and abiotic marine calcite have a similar range of Mg contents (0 to 22 and 4 to 21 mol% MgCO 3, respectively), yet biotic calcite has Sr 2+ concentrations that are consistently 1250 ppm higher than those of abiotic calcite. As in laboratory experiments, a positive linear relation is observed between DSr and calcite Mg content. This produces two distinct linear trends on a plot of Sr 2+ vs. Mg 2+ concentrations. Principal axes of variation for both trends have similar slopes, yet distinctly different Sr 2+ concentration intercepts. (Biotic: y = 0.024 x + 1298, r2 = 0.70; Abiotic: y = 0.027 x + 47, r2 = 0.77). The similar slopes of these trends reflect the constancy of Mg/Ca and Sr/Ca ratios of modern seawater. Equations describing the dependence of DSr on calcite Mg content are derived from both trends (Biotic: DSr = 3.16 x 10 t-6 (ppm Mg) + 0.169; Abiotic: DSr = 3.52 x 10 -6 (ppm Mg) + 0.0062). Characterization of Sr-Mg trends for Holocene materials allows comparison with analogous trends from ancient samples to estimate relative changes in seawater Mg/Ca and Sr/Ca ratios. The relatively high Sr contents of biotic calcite result from rapid precipitation rates associated with shell accretion in marine organisms. Calcites precipitated from seawater in laboratory experiments have Dsr values that are similar to those of biotic marine calcite, suggesting that both precipitate at approximately the same rate. Our estimates of surface area-normalized precipitation rates in planktonic and benthonic foraminifera are comparable to those of seeded, pH-stat experiments. We conclude that the DSr values for biotic and experimental marine calcite are kinetically controlled, whereas the lower precipitation rates of abiotic marine calcite yield DSr values that approximate equilibrium conditions. Experimentally derived equations describing the relation between DSr and calcite precipitation rate indicate that the offset in Sr content between biotic and abiotic calcite is the result of abiotic precipitation rates that are two to five orders of magnitude lower than those of biotic precipitates. However, observations of naturally occurring marine cements suggest that the five-order-of-magnitude offset best represents natural system processes.

  11. Growth and Dissolution of Calcite in the Presence of Adsorbed Stearic Acid.

    PubMed

    Ricci, Maria; Segura, Juan José; Erickson, Blake W; Fantner, Georg; Stellacci, Francesco; Voïtchovsky, Kislon

    2015-07-14

    The interaction of organic molecules with the surface of calcite plays a central role in many geochemical, petrochemical, and industrial processes and in biomineralization. Adsorbed organics, typically fatty acids, can interfere with the evolution of calcite when immersed in aqueous solutions. Here we use atomic force microscopy in liquid to explore in real-time the evolution of the (1014) surface of calcite covered with various densities of stearic acid and exposed to different saline solutions. Our results show that the stearic acid molecules tend to act as "pinning points" on the calcite's surface and slow down the crystal's restructuring kinetics. Depending on the amount of material adsorbed, the organic molecules can form monolayers or bilayer islands that become embedded into the growing crystal. The growth process can also displaces the organic molecules and actively concentrate them into stacked multilayers. Our results provide molecular-level insights into the interplay between the adsorbed fatty acid molecules and the evolving calcite crystal, highlighting mechanisms that could have important implications for several biochemical and geochemical processes and for the oil industry. PMID:26087312

  12. Mechanism of calcite co-orientation in the sea urchin tooth.

    PubMed

    Killian, Christopher E; Metzler, Rebecca A; Gong, Y U T; Olson, Ian C; Aizenberg, Joanna; Politi, Yael; Wilt, Fred H; Scholl, Andreas; Young, Anthony; Doran, Andrew; Kunz, Martin; Tamura, Nobumichi; Coppersmith, Susan N; Gilbert, P U P A

    2009-12-30

    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(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 (muXRD). 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(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. PMID:19954232

  13. Reaction of citric acid with calcite

    Microsoft Academic Search

    M. H. Al-Khaldi; H. A. Nasr-El-Din; S. Mehta; A. D. Al-Aamri

    2007-01-01

    The reaction of citric acid with calcite was investigated using the rotating disk apparatus. The effects of disk rotational speed, system pressure, and presence of magnesium and ferric ions on this reaction were examined. Scanning electron microscope (SEM) was also used to characterize the surface of the calcite disks at the end of each experiment.The reaction of citric acid and

  14. HEMATITE AND CALCITE COATINGS ON FOSSIL VERTEBRATES

    Microsoft Academic Search

    HUIMING BAO; PAUL L. KOCH; ROBERT P. HEPPLE

    Hematite coatings are common on vertebrate fossils from Paleocene\\/Eocene paleosol deposits in the Bighorn Basin, Wyoming. In general, hematite coatings are found only on fossils and are limited to soils exhibiting hydromorphic features and moderate maturity. Pet- rographic and isotopic evidence suggests that hematite and micritic calcite formed at nearly the same time in a pedogenic environment, whereas sparry calcite

  15. [Study on microarea characteristics of calcite in Archaean BIF from Wuyang area in south margin of North China Craton and its geological significances].

    PubMed

    Li, Hong-Zhong; Zhai, Ming-Guo; Zhang, Lian-Chang; Yang, Zhi-Jun; Zhou, Yong-Zhang; Wang, Chang-Le; Liang, Jin; Luo, An

    2013-11-01

    The results of Raman, SEM, CL and EDS analysis show that the quartz-type BIF (banded iron formation) in Tieshanmiao formation, from Wuyang area of south North China Craton mainly contains quartz, magnetite and a small quantity of calcite. In comparison, magnetites represent the highest automorphic degree, while calcites contribute to the lowest automorphic degree. In addition, the automorphic degree of the quartz lies between magnetite and calcite. In the results of Raman analysis, the crystallinity and order degree are quite diverse in the vertical direction of the calcite band-like, and this is different from the calcite vein precipitating from the upper hydrothermal fluid. There are obvious plastic flow happening to calcite particles. During the process of plastic flow, the calcites are finally filled in the space between quartz and magnetite. This is the reason why the cross sectional shape and distributional characteristics of calcite aggregate are controlled by the particles of quartz and magnetite, which is also evidenced by the calcite filled into the slight interspace between two particles of quartz. In the Raman analysis, there are apparent differences of microarea component in calcite band-like, and this denotes that it is produced by the plastic flow and concourse process. What's more, the calcite acts as the migration intermedium of tiny magnetite during their concourse and crystallization processes, which is witnessed by the concentrated particles of magnetite in small size in local parts of the calcites. With the help of calcite, the small magnetite particles join together to crystallize with bigger size or form aggregate of minerals. PMID:24555381

  16. 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

  17. Seed crystals and catalyzed epitaxy of single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Wang, Yuhuang

    This thesis demonstrates the continued growth of single-walled carbon nanotubes (SWNTs) from seeded SWNTs in a way analogous to epitaxy or cloning; that is, the SWNTs grow as a seamless extension to the existing seeded SWNTs and have the same diameter and chirality as those of the SWNT seeds. The experiments were carried out in three key steps, including: (1) preparing a macroscopic array of open-ended SWNTs; (2) reductively docking transition metals as a catalyst to the nanometer-sized open ends; and then (3) heating the whole up to 700--850°C in the presence of a carbon feedstock such as ethanol or ethylene. The resulting SWNT ropes inherit the diameters and chirality from the seeded SWNTs, as indicated by the closely matched frequencies of Raman radial breathing modes before and after the growth. As a control, only sparse nanotubes grew from closed-ended SWNTs, ruling out spontaneous nucleation as a dominating mechanism in our experiments. This experiment proved for the first time the growth of SWNTs can be separated from the nucleation step. The ability to separate the typically inefficient nucleation step from the growth of SWNTs and to restart the growth opens the possibility of amplifying SWNTs with only the desired (n, m). The success in the continued growth was enabled with the creation of macroscopic arrays of open-ended SWNTs from a neat SWNT fiber. A variety of techniques including cryo-microtoming and surface etching chemistry have been developed to produce a macroscopic (˜1200mum2), aligned, and clean---largely free of amorphous carbon, oxides, and metal residuals---SWNT substrate with open-ended SWNTs aligned along the fiber axis. Alternatively, the fiber was milled perpendicular to the fiber axis with a gallium focused ion beam to produce a planar, free-standing, ultra-thin, "bed-of-nails" SWNT membrane---a single layer of parallel SWNTs densely packed and aligned along the normal of the membrane.

  18. Sorption of phosphate onto calcite; results from batch experiments and surface complexation modeling

    NASA Astrophysics Data System (ADS)

    Ugilt Sø, Helle; Postma, Dieke; Jakobsen, Rasmus; Larsen, Flemming

    2011-05-01

    The adsorption of phosphate onto calcite was studied in a series of batch experiments. To avoid the precipitation of phosphate-containing minerals the experiments were conducted using a short reaction time (3 h) and low concentrations of phosphate (?50 ?M). Sorption of phosphate on calcite was studied in 11 different calcite-equilibrated solutions that varied in pH, P, ionic strength and activity of Ca 2+, CO32- and HCO3-. Our results show strong sorption of phosphate onto calcite. The kinetics of phosphate sorption onto calcite are fast; adsorption is complete within 2-3 h while desorption is complete in less than 0.5 h. The reversibility of the sorption process indicates that phosphate is not incorporated into the calcite crystal lattice under our experimental conditions. Precipitation of phosphate-containing phases does not seem to take place in systems with ?50 ?M total phosphate, in spite of a high degree of super-saturation with respect to hydroxyapatite (SI HAP ? 7.83). The amount of phosphate adsorbed varied with the solution composition, in particular, adsorption increases as the CO32- activity decreases (at constant pH) and as pH increases (at constant CO32- activity). The primary effect of ionic strength on phosphate sorption onto calcite is its influence on the activity of the different aqueous phosphate species. The experimental results were modeled satisfactorily using the constant capacitance model with >CaPO 4Ca 0 and either >CaHPO 4Ca + or > CaHPO4- as the adsorbed surface species. Generally the model captures the variation in phosphate adsorption onto calcite as a function of solution composition, though it was necessary to include two types of sorption sites (strong and weak) in the model to reproduce the convex shape of the sorption isotherms.

  19. Unravelling the enigmatic origin of calcitic nanofibres in soils and caves: purely physicochemical or biogenic processes?

    NASA Astrophysics Data System (ADS)

    Bindschedler, S.; Cailleau, G.; Braissant, O.; Millière, L.; Job, D.; Verrecchia, E. P.

    2014-01-01

    Calcitic nanofibres are ubiquitous habits of secondary calcium carbonate (CaCO3) accumulations observed in calcareous vadose environments. Despite their widespread occurrence, the origin of these nanofeatures remains enigmatic. Three possible mechanisms fuel the debate: (i) purely physicochemical processes, (ii) mineralization of rod-shaped bacteria, and (iii) crystal precipitation on organic templates. Nanofibres can be either mineral (calcitic) or organic in nature. They are very often observed in association with Needle Fibre Calcite (NFC), another typical secondary CaCO3 habit in terrestrial environments. This association has contributed to some confusion between both habits, however they are truly two distinct calcitic features and their recurrent association is likely to be an important fact to help understanding the origin of nanofibres. In this manuscript the different hypotheses that currently exist to explain the origin of calcitic nanofibres are critically reviewed. In addition to this, a new hypothesis for the origin of nanofibres is proposed based on the fact that current knowledge attributes a fungal origin to NFC. As this feature and nanofibres are recurrently observed together, a possible fungal origin for nanofibres which are associated with NFC is investigated. Sequential enzymatic digestion of the fungal cell wall of selected fungal species demonstrates that the fungal cell wall can be a source of organic nanofibres. The obtained organic nanofibres show a striking morphological resemblance when compared to their natural counterparts, emphasizing a fungal origin for part of the organic nanofibres observed in association with NFC. It is further hypothesized that these organic nanofibres may act as templates for calcite nucleation in a biologically-influenced mineralization process, generating calcitic nanofibres. This highlights the possible involvement of Fungi in CaCO3 biomineralization processes, a role still poorly documented at present-day. Moreover, on a global scale, the organomineralization of organic nanofibres into calcitic nanofibres might have a great, however overlooked, impact on the biogeochemical cycles of both Ca and C.

  20. Unravelling the enigmatic origin of calcitic nanofibres in soils and caves: purely physicochemical or biogenic processes?

    NASA Astrophysics Data System (ADS)

    Bindschedler, S.; Cailleau, G.; Braissant, O.; Millière, L.; Job, D.; Verrecchia, E. P.

    2014-05-01

    Calcitic nanofibres are ubiquitous habits of secondary calcium carbonate (CaCO3) accumulations observed in calcareous vadose environments. Despite their widespread occurrence, the origin of these nanofeatures remains enigmatic. Three possible mechanisms fuel the debate: (i) purely physicochemical processes, (ii) mineralization of rod-shaped bacteria, and (iii) crystal precipitation on organic templates. Nanofibres can be either mineral (calcitic) or organic in nature. They are very often observed in association with needle fibre calcite (NFC), another typical secondary CaCO3 habit in terrestrial environments. This association has contributed to some confusion between both habits, however they are truly two distinct calcitic features and their recurrent association is likely to be an important fact to help understanding the origin of nanofibres. In this paper the different hypotheses that currently exist to explain the origin of calcitic nanofibres are critically reviewed. In addition to this, a new hypothesis for the origin of nanofibres is proposed based on the fact that current knowledge attributes a fungal origin to NFC. As this feature and nanofibres are recurrently observed together, a possible fungal origin for nanofibres which are associated with NFC is investigated. Sequential enzymatic digestion of the fungal cell wall of selected fungal species demonstrates that the fungal cell wall can be a source of organic nanofibres. The obtained organic nanofibres show a striking morphological resemblance when compared to their natural counterparts, emphasizing a fungal origin for part of the organic nanofibres observed in association with NFC. It is further hypothesized that these organic nanofibres may act as templates for calcite nucleation in a biologically influenced mineralization process, generating calcitic nanofibres. This highlights the possible involvement of fungi in CaCO3 biomineralization processes, a role still poorly documented. Moreover, on a global scale, the organomineralization of organic nanofibres into calcitic nanofibres might be an overlooked process deserving more attention to specify its impact on the biogeochemical cycles of both Ca and C.

  1. Crystallization and preliminary X-ray diffraction analysis of the lectin from Canavalia boliviana Piper seeds

    PubMed Central

    Moura, Tales Rocha; Bezerra, Gustavo Arruda; Bezerra, Maria Julia Barbosa; Teixera, Cícero Silvano; Bezerra, Eduardo Henrique Salviano; Benevides, Raquel Guimarães; da Rocha, Bruno Anderson Matias; de Souza, Luiz Augusto Gomes; Delatorre, Plínio; Nagano, Celso Shiniti; Cavada, Benildo Sousa

    2009-01-01

    Plant lectins are the most studied group of carbohydrate-binding proteins. Despite the high similarity between the members of the Diocleinae subtribe (Leguminosae) group, they present differing biological activities. Canavalia boliviana lectin (Cbol) was purified using a Sephadex G-50 column and crystallized in the presence of X-Man by hanging-drop vapour diffusion at 293?K. After optimization, crystals suitable for diffraction were obtained under the condition 0.1?M HEPES pH 7.5 and 3.0?M sodium formate. The crystal belonged to the monoclinic space group C2, with unit-cell parameters a = 126.70, b = 66.64, c = 64.99?Å, ? = 90.0, ? = 120.8, ? = 90.0°. Assuming the presence of a dimer in the asymmetric unit, the solvent content was estimated to be about 46%. A complete data set was collected at 1.5?Å resolution. PMID:19255467

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

    PubMed Central

    Delatorre, Plínio; Nascimento, Kyria Santiago; Melo, Luciana Magalhães; de Souza, Emmanuel Prata; da Rocha, Bruno Anderson Matias; Benevides, Raquel G.; de Oliveira, Taiana Maia; Bezerra, Gustavo Arruda; Bezerra, Maria Júlia Barbosa; da Cunha, Rodrigo Maranguape Silva; da Cunha, Francisco Assis Bezerra; Freire, Valder Nogueira; Cavada, Benildo Sousa

    2006-01-01

    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. PMID:16511292

  3. Trace concentration - Huge impact: Nitrate in the calcite/Eu(III) system

    NASA Astrophysics Data System (ADS)

    Hofmann, Sascha; Voïtchovsky, Kislon; Schmidt, Moritz; Stumpf, Thorsten

    2014-01-01

    The interactions of trivalent lanthanides and actinides with secondary mineral phases such as calcite is of high importance for the safety assessment of deep geological repositories for high level nuclear waste (HLW). Due to similar ionic radii, calcium-bearing mineral phases are suitable host minerals for Ln(III) and An(III) ions. Especially calcite has been proven to retain these metal ions effectively by both surface complexation and bulk incorporation. Since anionic ligands (e.g., nitrate) are omnipresent in the geological environment and due to their coordinating properties, their influence on retentive processes should not be underestimated. Nitrate is a common contaminant in most HLW forms as a result of using nitric acid in fuel reprocessing. It is also formed by microbial activity under aerobic conditions. In this study, atomic force microscopy investigations revealed a major influence of nitrate upon the surface of calcite crystals. NaNO3 causes serious modifications even in trace amounts (<10-7 M) and forms a soft surface layer of low crystallinity on top of the calcite crystal. Time-resolved laser fluorescence spectroscopy of Eu(III) showed that, within this layer, Eu(III) ions are incorporated, while losing most of their hydration shell. The results show that solid solution modelling for actinides in calcite must take into account the presence of nitrate in pore and ground waters.

  4. Preliminary Results of Bacteria Distribution in Chinese Loess and Their Control on the Calcite Formation

    NASA Astrophysics Data System (ADS)

    Chen, Y.; Lian, B.; Hu, Q.; Teng, H. H.; Wu, T.; Ji, J.; Chen, J.

    2005-12-01

    Continuous loess-paleosol sequences on the Chinese Loess Plateau are viewed as one of best continental archives of paleoclimatic and paleoenvironmental changes of the Late Cenozoic era. Carbonate, mainly calcite, commonly occurs throughout the entire sequence; though some are detrital, most are in-situ pedogenic. TEM studies have shown various morphologies of calcites in Chinese loess, especially nano-rod calcite widely occurring in loess and paleosols which are biogenic. In this study, we collected fresh and undisturbed loess and paleosol samples and successfully separated dominant microbial communities. These microbes are mainly bacteria, especially Bacillus anthracis, and a few fungi. The amount of bacteria decreases sharply with the depth. Then we added the bacteria into the near saturated solution of CaCl2 and Na2CO3. It is interesting that the original calcite crystals formed under abiotic conditions changed from quadrilateral face to pentagonal or hexagonal and the crystal size enlarged almost twice. SEM and AFM observations display bacteria control on the growth of calcite, which cause the lighter carbon isotopic ratios.

  5. Eu3+ uptake by calcite: preliminary results from coprecipitation experiments and observations with surface-sensitive techniques.

    PubMed

    Stipp, S L S; Lakshtanov, L Z; Jensen, J T; Baker, J A

    2003-03-01

    A lack of information in databases for contamination risk assessment about the transport behaviour of the trivalent f-orbital elements in groundwater systems where calcite is at equilibrium motivated this study of Eu(3+) uptake. The free drift technique was used to examine the effects of Eu(3+) concentration, presence of Na(+) or K(+) and temperature, as well as calcite nucleation and precipitation kinetics, on the partitioning of calcite. Changes in surface composition and morphology resulting from exposure of single crystals of Iceland spar to Eu(3+)-bearing solutions were observed with X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). First results confirm that calcite has high affinity for Eu(3+). Rates of nucleation and precipitation strongly affect the extent of uptake but the presence of Na(+) and K(+) has no effect, suggesting formation of solid solution as CaCO(3)-EuOHCO(3). Surface-sensitive techniques prove that Eu(3+) is adsorbed to calcite even when the surface is dissolving and adsorption is not accompanied by precipitation of a separate Eu(3+)-solid phase. Adsorbed Eu modifies calcite's dissolution behaviour, roughening terraces and rounding step edges, and producing surface morphology where some surface sites appear blocked. Results imply that Eu(3+) concentrations in natural calcites are limited by Eu(3+) availability rather than by a lack of ability to fit into calcite's atomic structure. This behaviour can probably be expected for other trivalent rare Earth elements (REE), actinides and fission products whose behaviour is similar to that of Eu(3+). These elements are likely to be incorporated within the calcite bulk in systems where it is precipitating and the demonstrated strong partitioning ensures some uptake even where calcite is at or under saturation. PMID:12598092

  6. 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.

  7. 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.

  8. Polymorphism of calcite at high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Merlini, Marco

    2015-04-01

    Carbonates may play a fundamental role as carbon repository phases in the Earth's interior[1]. Recent crystal structure determinations by single crystal diffraction technique at high pressure [2] have shown that these phases may adopt very complex structures at pressures corresponding to Earth's upper and lower mantle. Calcite, CaCO3, transforms to low symmetry phases. Computational studies have confirmed that some of these polymorphs, CaCO3-VI in particular, are thermodynamically stable compared to calcite and aragonite. We investigated also the high temperature polymorphism, by experiments at controlled atmosphere and we confirmed the recently proposed CaCO3-V structure [3] above 1000°C and ambient pressure. In-situ experiments at simultaneous high pressure and temperature defined more accurately the phase relationship between these polymorphs and the effect of Mg and Fe substitution. 1. R. M. Hazen, A. P. Jones, J. A. Baross ed., Reviews in Mineralogy and Geochemistry, 75 (2013). 2. M. Merlini, M. Hanfland, High Pressure Research 33, 511-522 (2013). 3. N. Ishizawa et al., Scientific Reports, 3, 2832 (2013).

  9. Acidic mine drainage in carbonate terrains: geochemical processes and rates of calcite dissolution

    NASA Astrophysics Data System (ADS)

    Wicks, Carol M.; Groves, Christopher G.

    1993-06-01

    In situ rates of calcite dissolution were measured by weight loss of single crystals placed in an East Tennessee stream that is affected by acidic mine drainage. The dissolution rates ranged from 2.6 × 10 -8 to 7.9 × 10 -8 mmol cm -2 s -1 over the entire pH range of 3.6-7.7. Calcite dissolution rates were several orders of magnitude slower than observed in laboratory solutions of CO 2-HCl-H 2O-CaCO 3 and appeared to be inhibited by dissolved iron and possibly other solutes in the stream.

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

    SciTech Connect

    Bracco, Jacquelyn N [ORNL; Stack, Andrew G [ORNL; Steefel, Carl I [Lawrence Berkeley National Laboratory (LBNL)

    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.

  11. Ultra-high-speed lateral solid phase crystallization of GeSn on insulator combined with Sn-melting-induced seeding

    NASA Astrophysics Data System (ADS)

    Chikita, H.; Matsumura, R.; Kai, Y.; Sadoh, T.; Miyao, M.

    2014-11-01

    To produce high-performance devices on flexible plastic substrates, it is essential to form Ge-based group IV semiconductors on insulating substrates at low temperatures (?250 °C). We have developed a technique for solid phase crystallization of amorphous GeSn (?220 °C) enhanced by Sn doping, and combined with a seeding technique induced by Sn melting (˜250 °C). This combination produces lateral crystallization of amorphous GeSn from seed arrays with no incubation time. As a result, extremely high growth velocities at 220 °C, depending on Sn concentration, e.g., 0.13 ?m/h (14% Sn) and 1100 ?m/h (23% Sn), are achieved. These velocities are 104-108 times higher than that of pure Ge. This technique enables growth of crystalline GeSn island arrays (diameters: 50-150 ?m) at low temperatures (?250 °C) at controlled positions on insulating substrates.

  12. Simulation of rocket seeding of convective clouds with coarse-dispersion hygroscopic aerosol. 1. Condensational growth of the cloud droplets at the salt crystals

    Microsoft Academic Search

    M. K. Zhekamukhov; A. M. Abshaev

    2009-01-01

    Patterns of propagation of aerosol particles generated in the hygroscopic seeding of convective clouds from antihail rockets\\u000a is studied. Effects of the salt particle dispersity on condensational growth rate of separate cloud droplets on these particles\\u000a are studied; analytical formulas are obtained as describing change of radius of the NaCl crystal and of the cloud droplet\\u000a which grows on the

  13. 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.

  14. Hydrodynamic Instabilities in Czochralski Process of Crystal Growth - Effect of Varying The Seed to Crucible Radii Ratio

    NASA Astrophysics Data System (ADS)

    Rosenstein, Y.; Bar-Yoseph, P. Z.

    2007-04-01

    This paper deals with axisymmmetry breaking instabilities in Czochralski process of crystal growth. Numerical linear stability analysis was carried out using the axisymmetric bulk flow model. Stability diagrams of critical Grashof numbers G?c and frequencies ?c dependent on aspect ratio ?( = height/radius), 0.4 <= ? <= 1.0 and Prandtl number P? = 0.01 are shown. Computations were carried out using the spectral element method in the meridional plane with Fourier decomposition in the azimuthal direction. It was found that convective instability sets in through an Hopf bifuraction. For P? = 0.01 computations were carried out for the first 10 modes, only the first 5 (0,1,2,3,4) were important. Sensitivity of mode transitions was observed at parameter range of ? > 0.65 and in some regions modes were observed approaching each other closely. For 0.4 <= ? <= 0.85 and P? = 0.01 dispersion relation analysis reveals convective instability effects while for larger ? rotational effects appear. Comparative study shows that for seed to crucible ratio ? = Rx/Rc = 0.4, 0.5 different pathologies are observed. While mode switches at ? = 0.4 are many and modes approach each other closely, different behaviour is observed at ? = 0.5 which is quite regular.

  15. 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.

  16. Transformation mechanism of amorphous calcium carbonate into calcite in the sea urchin larval spicule

    PubMed Central

    Politi, Yael; Metzler, Rebecca A.; Abrecht, Mike; Gilbert, Benjamin; Wilt, Fred H.; Sagi, Irit; Addadi, Lia; Weiner, Steve; Gilbert, P. U. P. A.

    2008-01-01

    Sea urchin larval spicules transform amorphous calcium carbonate (ACC) into calcite single crystals. The mechanism of transformation is enigmatic: the transforming spicule displays both amorphous and crystalline properties, with no defined crystallization front. Here, we use X-ray photoelectron emission spectromicroscopy with probing size of 40–200 nm. We resolve 3 distinct mineral phases: An initial short-lived, presumably hydrated ACC phase, followed by an intermediate transient form of ACC, and finally the biogenic crystalline calcite phase. The amorphous and crystalline phases are juxtaposed, often appearing in adjacent sites at a scale of tens of nanometers. We propose that the amorphous-crystal transformation propagates in a tortuous path through preexisting 40- to 100-nm amorphous units, via a secondary nucleation mechanism. PMID:18987314

  17. High-Performance Ferroelectric Bi4Ti3O12 Single Crystals Grown by Top-Seeded Solution Growth Method under High-Pressure Oxygen Atmosphere

    NASA Astrophysics Data System (ADS)

    Kitanaka, Yuuki; Noguchi, Yuji; Miyayama, Masaru

    2010-09-01

    The top-seeded solution growth (TSSG) method under high oxygen pressure (PO2 ) atmosphere has been developed to obtain large high-performance single crystals of ferroelectric Bi4Ti3O12. Crystals grown at 960 °C at a PO2 of 0.9 MPa exhibited well-saturated hysteresis with a remanent polarization of 48 µC/cm2 and a coercive field of 29 kV/cm. The results of piezoresponse force microscopy indicate that polarization switching is accomplished throughout the crystals. Electric-field-induced strain measurements along the a axis yield a piezoelectric constant d11* of 37 pm/V for Bi4Ti3O12.

  18. The coordination and distribution of B in foraminiferal calcite

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    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 cycle, and ocean acidification processes. However, discrepancies between the theory underpinning the B proxies, and mineralogical observations of B coordination in biomineral carbonates call the basis of these proxies into question. Here, we use synchrotron X-ray spectromicroscopy to show that B is hosted solely as trigonal BO3 in the calcite test of Amphistegina lessonii, and that B concentration exhibits banding at the micron length scale. In contrast to previous results, our observation of trigonal B agrees with the predictions of the theoretical mechanism behind B palaeoproxies. These data strengthen the use of B for producing palaeo-pH records. The observation of systematic B heterogeneity, however, highlights the complexity of foraminiferal biomineralisation, implying that B incorporation is modulated by biological or crystal growth processes.

  19. EXAFS Characterization of Uranyl Interaction at the Calcite-Water Interface

    NASA Astrophysics Data System (ADS)

    Reeder, R. J.; Elzinga, E. J.; Tait, C. D.

    2002-12-01

    Recent studies using X-ray absorption and luminescence spectroscopies have demonstrated uptake and incorporation of uranyl by calcite. X-ray microprobe studies on uranyl-reacted calcite single crystals reveal that uranyl exhibits preferences for specific surface sites. These preferences are likely expressed upon adsorption of uranyl species at the calcite-water interface. We have used X-ray absorption fine structure (EXAFS), combined with luminescence spectroscopy, to characterize the interactions of uranyl carbonate species with the calcite surface in the pH range 7.4-8.3. To minimize the potential for dissolution or precipitation, solutions were pre-equilibrated with reagent calcite powder for 3 weeks, with pH stabilizing at 8.3. For other experiments, the pH was adjusted initially to achieve a final pH of 7.4 after aging for 3 weeks. Uranyl carbonate solution was added to the pre-equilibrated suspensions to achieve initial U(VI) concentrations ranging from 5 uM to 5 mM. Suspensions were filtered to recover the calcite, but were kept moist to retain the sorbed complexes at the calcite-water interface. Multiple EXAFS spectra were collected using a multi-element Ge detector at beamline 12-BM at the APS and analyzed using standard methods. Fourier transforms (FT) of the spectra contain features corresponding to two axial oxygens and a shell of equatorial oxygens, as well as weaker features at higher R. For suspensions having initial U(VI) concentrations from 5-100 uM, a shoulder is observed in the FT on the high-R side of the equatorial oxygen, and fitting suggests minor splitting of this shell. For higher initial U(VI) concentrations, including the highest U(VI) concentration, 5 mM, the splitting becomes more pronounced. Weak features in the FT at higher-R can be fitted with backscattering from carbon, oxygen, and calcium shells, although fits without calcium provide nearly the same agreement. Luminescence spectroscopy reveals the presence of multiple uranyl species sorbed on the calcite from suspensions with 100 uM U(VI) and lower concentrations. The presence of multiple species may account for the splitting of the equatorial coordination indicated by EXAFS. For higher U(VI) concentrations, the luminescence results are consistent with formation of a schoepite-like precipitate. Understanding the complex interactions of uranyl at the calcite-water interface requires complementary data from multiple techniques.

  20. Characteristics of biogenic calcite in the prismatic layer of a pearl oyster, Pinctada fucata.

    PubMed

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

    2010-10-01

    The fine structure of the calcite prism in the outer layer of a pearl oyster, Pinctada fucata, has been investigated using various electron beam techniques, in order to understand its characteristics and growth mechanism including the role of intracrystalline organic substances. As the calcite prismatic layer grows thicker, sinuous boundaries develop to divide the prism into a number of domains. The crystal misorientation between the adjacent domains is several to more than ten degrees. The component of the misorientation is mainly the rotation about the c-axis. There is no continuous organic membrane at the boundaries. Furthermore, the crystal orientation inside the domains changes gradually, as indicated by the electron back-scattered diffraction (EBSD) in a scanning electron microscope (SEM). Transmission electron microscopy (TEM) examination revealed that the domain consists of sub-grains of a few hundred nanometers divided by small-angle grain boundaries, which are probably the origin of the gradual change of the crystal orientation inside the domains. Spherular Fresnel contrasts were often observed at the small-angle grain boundaries, in defocused TEM images. Electron energy-loss spectroscopy (EELS) indicated the spherules are organic macromolecules, suggesting that incorporation of organic macromolecules during the crystal growth forms the sub-grain structure of the calcite prism. PMID:20558074

  1. Post-deformational annealing of calcite rocks

    NASA Astrophysics Data System (ADS)

    Barnhoorn, Auke; Bystricky, Misha; Burlini, Luigi; Kunze, Karsten

    2005-07-01

    The evolution of microstructure and crystallographic preferred orientation (CPO) during post-deformational annealing was studied on three calcite rock types differing in purity and grain size: Carrara marble (98% calcite, mean grain size of 115 ?m), Solnhofen limestone (96%, 5 ?m) and synthetic calcite aggregates (99%, 7 ?m). Samples were first deformed in torsion at 727 °C at a shear strain rate of 3 × 10 - 4 s - 1 to a shear strain of 5 and subsequently heat-treated at 727 °C for various durations between 0 and 24 h. Microstructures and CPOs were analysed by optical microscopy, image analysis and electron backscatter diffraction (EBSD). All rock types deformed in the dislocation creep field at the same applied conditions, but their microstructures and CPOs after deformation and after annealing differed depending on starting grain size and material composition. In Carrara marble and in the synthetic calcite aggregate, a strong CPO developed during deformation accompanied by dynamic recrystallisation with significant changes in grain size. During annealing, widespread grain growth and subtle changes of CPO occurred, and equilibrated foam microstructures were approached after long annealing times. The CPO is the only feature in annealed samples indicating an earlier deformation phase, although it is not always identical to the CPO formed during deformation. In the more impure Solnhofen limestone, secondary phases on grain boundaries suppressed grain boundary mobility and prevented both the formation of a recrystallisation CPO during deformation and grain size modification during deformation and annealing.

  2. 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…

  3. Structural evolution of calcite at high temperatures: Phase V unveiled

    PubMed Central

    Ishizawa, Nobuo; Setoguchi, Hayato; Yanagisawa, Kazumichi

    2013-01-01

    The calcite form of calcium carbonate CaCO3 undergoes a reversible phase transition between Rc and Rm at ~1240?K under a CO2 atmosphere of ~0.4?MPa. The joint probability density function obtained from the single-crystal X-ray diffraction data revealed that the oxygen triangles of the CO3 group in the high temperature form (Phase V) do not sit still at specified positions in the space group Rm, but migrate along the undulated circular orbital about carbon. The present study also shows how the room temperature form (Phase I) develops into Phase V through an intermediate form (Phase IV) in the temperature range between ~985?K and ~1240?K. PMID:24084871

  4. Crystals

    NSDL National Science Digital Library

    Lawrence Hall of Science

    2009-01-01

    In this earth science/math/art activity, learners use simple ingredients to grow crystals and examine the repeating geometric shapes and patterns. Learners compare the growth of crystals from four types of crystal-starters (table salt, Borax, sand, and Epsom salt) to see which starter grows the most crystals in 14 days. Learners report their results online and find out what other learners discovered. Afterward, learners can use the crystals they grew to create works of art.

  5. Single-contact pressure solution creep on calcite monocrystals

    E-print Network

    Paris-Sud XI, Université de

    and in a calcite-saturated aqueous solution of NH4Cl. The deformation (depth of the hole below the indenter temperature in a saturated aqueous solution of calcite. The displacement of the indenter was continuously in this solution. In contrast, the experiments conducted in a calcite-saturated aqueous solution show moderate

  6. 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.

  7. 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.

  8. 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.

  9. An experimental study of calcite and limestone dissolution rates as a function of pH from ?1 to 3 and temperature from 25 to 80°C

    Microsoft Academic Search

    Marwan Alkattan; Eric H Oelkers; Jean-Louis Dandurand; Jacques Schott

    1998-01-01

    Dissolution rates of single calcite crystals, limestones, and compressed calcite powders were determined from sample weight loss using free-drift rotating disk techniques. Experiments were performed in aqueous HCl solutions over the bulk solution pH range ?1 to 3, and at temperatures of 25°, 50°, and 80°C. Corresponding rates of the three different sample types are identical within experimental uncertainty. Interpretation

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. The transformation of vaterite to calcite: effect of the conditions of the solutions in contact with the mineral phase

    NASA Astrophysics Data System (ADS)

    Spanos, Nikos; Koutsoukos, Petros G.

    1998-08-01

    The transformation of the thermodynamically unstable vaterite into the stable calcite was investigated during the precipitation of calcium carbonate, under conditions of constant supersaturation at 25, 35 and 45°C and pHs 8.5, 9.0 and 10.0. The calcite content in the solid precipitates was determined quantitatively by the X-ray diffraction technique (XRD) using the appropriate mixed standards of known composition. Scanning electron microscopy (SEM) and particle number and size measurements were also used for the characterisation of the solid precipitates. It was found that the transformation of vaterite into calcite does not depend on pH and temperature in the range 25-45°C. It depends only on the supersaturation, and this, only at relatively high supersaturation ratios (1.5-1.9). Specifically, the rate of transformation decreases as supersaturation increases. It was suggested on the basis of the kinetics results, that the transformation takes place through dissolution of vaterite, preferably of the small crystals followed by the crystallisation of calcite. At relatively high supersaturation ratios (1.5-1.9) the transformation is controlled by the dissolution of vaterite, whereas at lower supersaturation ratios (1.2-1.5) the rate of dissolution of vaterite is similar with that of crystallisation of calcite. Finally, a model equation which predicts a linear dependence of the rate of transformation on supersaturation ratio has been derived at relatively high supersaturation ratios.

  16. 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.

  17. Polycrystalline calcite to aragonite transformation kinetics: experiments in synthetic systems

    Microsoft Academic Search

    Shueh-Jung Lin; Wuu-Liang Huang

    2004-01-01

    The kinetics of the calcite to aragonite transformation have been investigated using synthetic polycrystalline calcite aggregates, with and without additional minerals present. The reaction progresses as a function of time were measured at four temperature\\/pressure conditions: (1) 550 °C\\/1.86 GPa; (2) 600 °C\\/2.11 GPa; (3) 650 °C\\/2.11 GPa, and (4) 700 °C\\/2.29 GPa. Experiments reveal that Mg-calcite and Fe-calcite transforms to aragonite at considerably slower rates than pure

  18. Atomistic Simulations of Corrosion Inhibitors Adsorbed on Calcite Surfaces I. Force field Parameters for Calcite

    E-print Network

    Goddard III, William A.

    ARTICLES Atomistic Simulations of Corrosion Inhibitors Adsorbed on Calcite Surfaces I. Force field energetics for the various surfaces of interest are predicted. 1. Introduction Corrosion inhibitors for oil mechanism for corrosion inhibition of iron by imidazolines.1 Atomistic simulations have also been made

  19. Succeeding with seeding: some practical advice

    Microsoft Academic Search

    Terese Bergfors

    2007-01-01

    Seeding is a powerful and versatile method for optimizing crystal growth conditions. This article discusses, from a practical\\u000a point of view, what seeding is, the selection and transfer of seeds, and into what conditions they should be transferred.\\u000a The most common causes of failures in seeding experiments are also analyzed.

  20. The Coordination of Mg in Foraminiferal Calcite

    NASA Astrophysics Data System (ADS)

    Branson, O.; Redfern, S. A.; Tyliszczak, T.; Sadekov, A.; Langer, G.; Elderfield, H.

    2012-12-01

    The Mg/Ca ratio in calcite shells ('tests') of foraminifera is an empirical ocean temperature proxy widely used to interpret palaeoclimates. We explore the distribution and local environment of Mg in foram tests using STXM and NEXAFS spectroscopy to test the fundamental assumptions behind the proxy, and shed light on the mechanisms underpinning this vital oceanographic tool. Throughout the development of the Mg/Ca proxy, it has been assumed that Mg in foraminifera tests substitutes directly into the calcite lattice (1). This assumption is based on XRD analyses of various high-Mg biogenic carbonates, where Mg concentrations are manifest in the shifted position of diffraction peaks (2, 3). The extrapolation of this trend to foraminiferal calcite links the proxy to inorganic precipitation experiments, and provides a theoretical mechanistic framework to understand the link between Mg/Ca and temperature: the substitution of Mg is endothermic, and favoured at higher temperatures. However, the concentration of Mg in most foraminifera (0-10 mmol/mol Mg/Ca) is below the detection limit of XRD methods, and the analogy to inorganic systems has not been explicitly tested. Electron microprobe (4-6), LA-ICP-MS (7) and high-resolution nanoSIMS mapping (Sadekov, unpub.) of foraminifera tests have revealed the presence of high 'trace element' bands running in plane with the test surface, enriched in Mg, Sr, S, organic molecules and other trace elements. This emphasises a key question highlighted by Dodd (1) when the proxy was still in its infancy: how is Mg incorporated into mineral skeletons? By direct substitution into the calcite lattice, interstitially in a separate distinct mineral phase, or associated with organic compounds? We address this fundamental question using scanning transmission X-ray microscopy (STXM) and X-ray absorption spectroscopy at ALS beamline 11.0.2 to examine the distribution and local atomic environment of Mg in two contrasting species of foraminifera. Our data conclusively demonstrate that the Mg in the high- and low-trace element bands in the two different species is incorporated in the same mode. Foraminiferal Mg K-edge spectra are most similar to that of dolomite, where Ca and Mg are interchangeable and both present in octahedral sites. This indicates that Mg directly substitutes for Ca in the calcite test, validating the assumptions underlying the use of the Mg/Ca proxy. The uniformity of Mg environment also sheds light on the drivers of Mg heterogeneity, suggesting that Mg banding is driven by fluctuations in medium chemistry, rather than any change in Mg incorporation mechanism. The ultimate cause of Mg heterogeneity remains an open question, however. 1. J. R. Dodd, J Paleontology, 1313-1329 (1967). 2. K. E. Chave, J Geol 62, 266-283 (1954). 3. J. Titschack, F. Goetz-Neunhoeffer, J. Neubauer, Am Min 96, 1028 (2011). 4. J. Lipps, P. Ribbe, J Paleontology 41, 492-496 (1967). 5. A. Y. Sadekov, S. M. Eggins, P. de Deckker, G3 6, Q12P06 (2005). 6. J. Erez, Rev Min Geochem 54, 115 (2003). 7. A. Y. Sadekov, S. M. Eggins, G. P. Klinkhammer, Y. Rosenthal, Earth Planet Sc Lett 292, 312-324 (2010).

  1. 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

  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. An Interpretation of the Mechanisms of Ice-Crystal Formation Operative in the Lake Almanor Cloud-Seeding Program

    Microsoft Academic Search

    Steven K. Chai; William G. Finnegan; Richard L. Pitter

    1993-01-01

    In a 1984 85 winter cloud-seeding program at Lake Almanor, California, indium sesquioxide (In2O3) aerosol particle generators were collocated with silver iodide (AgI) aerosol particle generators as a source of inert tracer aerosol. The In2O3 aerosol served as an indicator of the amount of AgI aerosol scavenged. Based on the aerosol emission rates, if AgI aerosol was only captured by

  4. Oxygen isotope fractionation in quartz, albite, anorthite and calcite

    Microsoft Academic Search

    Robert N. Clayton; Julian R. Goldsmith; Toshiko K. Mayeda

    1989-01-01

    Laboratory measurements of equilibrium oxygen isotope fractionation in quartz, albite, anorthite, and calcite have been carried out by anhydrous exchange between silicates and calcite at temperatures of 600°C and above. Exchange in these systems is as rapid as exchange between silicates and water. In this paper results are compared with published theoretical estimates as well as data derived from hydrothermal

  5. Thermal and Evolved Gas Behavior of Calcite Under Mars Phoenix TEGA Operating Conditions

    Microsoft Academic Search

    B. Sutter; H. V. Lauer; D. C. Golden; W. V. Boynton; R. V. Morris; P. B. Niles; D. W. Ming

    2009-01-01

    Calcite may have been detected by the Thermal Evolved Gas Analyzer (TEGA) at the Phoenix lander site. Laboratory thermal analyses of calcite under TEGA operating conditions will be presented to aid the interpretation of calcite detection by TEGA.

  6. The influence of impurities on the growth rate of calcite

    NASA Astrophysics Data System (ADS)

    Meyer, H. J.

    1984-05-01

    The effects of 34 different additives on the growth rate of calcite were investigated. An initial growth rate of about one crystal monolayer (3 × 10 -8 cm) per minute was adjusted at a constant supersaturation which was maintained by a control circuit. Then the impurity was added step by step and the reduction of the growth rate was measured. The impurity concentration necessary to reduce the initial growth rate by a certain percentage increased in the order Fe 2+, ATP, P 3O 5-10, P 2O 4-7, (PO 3) 6-6, Zn 2+, ADP, Ce 3+, Pb 2+, carbamyl phosphate, Fe 3+, PO 3-4, Co 2+, Mn 2+, Be 2+, ?-glycerophosphate, Ni 2+, Cd 2+, "Tris", phenylphosphate, chondroitine sulphate, Ba 2+, citrate, AMP, Sr 2+, tricarballylate, taurine, SO 2-4, Mg 2+ by 4 orders of magnitude. The most effective additives halved the initial growth rate in concentrations of 2 × 10 -8 mol/1. For Fe 2+ the halving concentration was nearly proportional to the initial rate. The mechanism of inhibition by adsorption of the impurities at growth sites (kinks) is discussed.

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. Investigating the Physical Basis of Amorphous Precursor Transformation to Calcite Using Patterned Alkanethiol Surfaces

    NASA Astrophysics Data System (ADS)

    Wang, D.; Wallace, A.; Han, T. Y.; Lee, J. R.; Hailey, P. D.; de Yoreo, J. J.; Dove, P. M.

    2007-12-01

    Increasing evidence from X-ray Absorption Spectroscopy and Environmental Scanning Electron Microscopy (ESEM) studies of biominerals extracted from calcifying organisms show that amorphous calcium carbonate (ACC) plays a key role in the initial formation of carbonate minerals and in shaping them into complex morphologies. Echinoderms and possibly a wide variety of other organisms, use ACC as a precursor phase. The ACC is first formed within spatial and temporally controlled environments such as vesicles, followed by a subsequent onset of mineralization that transforms the precursor into a fully crystalline material. Recent studies on sea urchin embryos have shown that during this transformation, ACC develops short-range order that resembles calcite before fully crystallizing. While this "non-traditional" process is recognized, the mechanisms and factors that govern this transformation remain poorly understood. Of particular interest are the roles of water, and the functional group chemistry of surfaces and macromolecules within mineralization environments. To investigate these questions, we have developed an experimental approach using ESEM that allows us to control impurity concentration, surface functionality and water content through the degree of water condensation. Patterned self-assembled monolayers (SAM) of hydrophilic moieties with domains of approximately 25 microns in diameter are used to form an array of micro-reactors. ACC particles with known composition are then deposited on the patterns. Condensing water in the ESEM initializes the transformation of ACC to calcite. Our results show that in saturated water vapor, ACC swells, but no obvious faceting of the material occurs. It is only in bulk water, via dissolution/crystallization, where the calcite grown on carboxyl-terminated surfaces is found with the often-observed \\{013\\} nucleation face. We use this insight to understand the role of the different chemical moieties on ACC to calcite transformation by measuring nucleation rates with time resolved experiments in the ESEM using bulk water. Preliminary evidence shows a markedly lower nucleation rate on hydroxyl versus carboxyl surfaces suggesting that hydroxyl functionalized surfaces do not promote the nucleation of calcite thus stabilizing the amorphous phase.

  12. A pore scale description of calcium isotope exchange and equilibration with calcite

    NASA Astrophysics Data System (ADS)

    Druhan, J. L.; Huber, C.; Parmigiani, A.

    2014-12-01

    The distribution of stable isotope ratios between dissolved and solid phases are commonly used to assess processes of mineral formation, alteration and dissolution in a variety of low temperature systems. In order to model this partitioning, a description of isotopic exchange occurring at the fluid-solid surface is required. The use of continuum scale reactive transport models to describe heterogeneous isotopic fractionation is thus hindered by the ability to discretize isotopic gradients within a solid phase. Here we present a multi-component pore scale model for the partitioning of calcium isotopes between dissolved Ca2+ and calcite using a lattice Boltzmann method capable of describing the isotopic composition of an evolving mineral surface distinct from the bulk calcite composition. A key feature of our model is the ability to simultaneously track isotopic exchange at the fluid-solid surface as well as the isotopic composition of both bulk fluid and bulk calcite. This is significant in that the surface exchange dictates the evolution of isotopic compositions through time, while the bulk isotope ratios represent the actual measured values of samples collected in the field. Using this approach, we reexamine the distribution of calcium isotope ratios in pore fluids and carbonates reported for deep-sea core profiles with particular emphasis on interpretation of the equilibrium fractionation factor. Based on simulations of an initially supersaturated fluid surrounding a calcite crystal at a range of porosities, we show that the fluid can achieve both chemical and isotopic equilibrium with the solid surface while maintaining the appearance of disequilibrium with the bulk solid. The extent to which the final equilibrated calcium isotope ratio of the bulk fluid and bulk solid agree is therefore a function of the depth into the mineral surface that is exchangeable with the fluid.

  13. An oxygen isotope study of illite and calcite in three Appalachian Paleozoic vertic paleosols

    SciTech Connect

    Mora, C.I.; Sheldon, B.T.; Driese, S.G. [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Geological Sciences; Elliott, W.C. [Georgia State Univ., Atlanta, GA (United States). Dept. of Geology

    1998-05-01

    The oxygen isotope compositions of pedogenic calcite and illite in three Paleozoic vertic red bed paleosols record a complex history of pedogenic and diagenetic processes. The paleosols are preserved in the upper Mississippian (Chesterian) Mauch Chunk (Pennsylvania), Hinton (West Virginia), and Pennington (Tennessee) Formations in the Appalachian Basin and were buried to 7--8 km (230--260 C), 3--4 km (100--145 C), and 1.5--3 km (70--100 C), respectively. The submicron-size clay fractions of the paleosols are presently composed of R3-ordered illite/smectite (I/S), inferred from K-Ar dates and soil morphology to have been authigenically produced by the reaction of smectite to illite. Oxygen isotope fractionations, calculated pore-fluid compositions, and K-Ar dates were used to constrain the conditions and timing of I/S and pedogenic calcite (re)crystallization in each of the paleosols. The data were interpreted in light of three possible end-member environments for formation and recrystallization: (1) the pedogenic environment; (2) the burial diagenetic environment; and (3) a burial environment dominated by hot, tectonically driven fluid. The {delta}{sup 18}O values of pedogenic calcite and authigenic I/S in vertic red bed paleosols generally reflect recrystallization and exchange during burial diagenesis and are thus not suitable for interpretation of paleoenvironment or paleoclimate. The involvement of orogenic fluids during burial cannot be ruled out, but it is not required by any of the paleosols. In the coastal-margin Pennington Formation paleosol, I/S formation may have been initiated in the pedogenic environment in response to cyclical wetting and drying of the soil clay matrix. Continued smectite transformation and coarsening and ordering of I/S during a long period of shallow burial led to its isotopic reequilibration with pore fluids at slightly elevated temperature, but oxygen isotope compositions of pedogenic calcite in the paleosol are preserved.

  14. Experimental Study of Sr, Mg, and Ba Partitioning Into Calcite at Various Linear Growth Rates Using Elemental and Isotopic Spikes: Preliminary Results.

    NASA Astrophysics Data System (ADS)

    Gabitov, R. I.; Adkins, J. F.; Eiler, J. M.

    2007-12-01

    The ratios of Mg/Ca and Sr/Ca in calcium carbonates are widely used as paleothermometers. However, inconsistencies in the relationship between temperature and composition amongst inorganic and biogenic calcites suggest the influence of factors other than temperature, including precipitation rate. We examine the influence of growth rate on Mg, Sr, and Ba partition coefficients between calcite and aqueous fluid (Kdi= XiCalcite*XCaFluid/XCaCalcite*XiFluid, where i is the cation of interest and X is the mole fraction). Previous experimental studies of growth-rate-dependent partitioning were based on bulk analysis of carbonate precipitates; here we develop an alternative approach based on in situ measurements of single crystals having known linear growth rates. Experiments were performed by continuously adding two titrates (Na2CO3 and CaCl2) into growth solution of NaCl doped with trace elements. Linear growth rates of calcite crystals are determined by adding of elemental and isotopic spikes into the growth medium (episodically for elemental spikes; continuously for isotopic spikes). Harvested crystals were randomly mounted into high vacuum epoxy and examined with NanoSIMS and SEM techniques. Our NanoSIMS measurements of product calcite crystals document approximately concentric growth, the rate of which is marked by the sequential appearance of the various elemental and isotopic spikes we added to the parental fluid during growth. For example, ratios of 55Mn/42Ca in carbonate are 1e-5 in crystal cores and sharply increase up to 1.6e-3 in crystal rims, in response to our addition of Mn to the parental liquid at a known time. Similarly, the 26Mg/24Mg ratio is close to natural abundances in crystal cores and monotonically increases toward the crystal edges, reflecting monotonic addition of 26Mg spike throughout the experiment. Such data, combined with known timing of elemental spike additions and rates of increase of the 26Mg/24Mg ratio of the solution, permitted us to quantitatively reconstruct the growth histories of individual calcite crystals. Calcite growth rates were calculated as the ratio of the distance between two adjacent analytical spots and the corresponding time interval required to explain their difference in composition. This is straightforward for the portions of the experiments when 26Mg/24Mg changed monotonically at a known rate, but generally provides only limits to the growth rate during the period when elemental spikes were added episodically. The linear growth rates estimated in this way varied from 0.6 to 6 microns per hour, with uncertainties as good as 6 percents, relative. The lower edge of our growth rate interval is similar to those of benthonic foraminifera, suggesting that partitioning data based on our experiments will constrain growth-rate effects relevant to common paleothermometry applications. Note that the growth rates we derive could be under- estimates because analyzed sections of the crystals do no necessarily expose the center of calcite crystallization. We anticipate determining Sr/Ca, Mg/Ca, and Ba/Ca ratios in the fluid, after which we shall report the partition coefficients for Sr, Mg, and Ba as function of growth rate of the calcite crystals.

  15. 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.

  16. Trace metal distribution and isotope variations in low-temperature calcite and groundwater in granitoid fractures down to 1 km depth

    NASA Astrophysics Data System (ADS)

    Drake, Henrik; Tullborg, Eva-Lena; Hogmalm, K. Johan; Åström, Mats E.

    2012-05-01

    Studies of low-temperature fracture calcite in Proterozoic or Archaean crystalline rocks are very limited, mainly because this calcite usually is, first, not very abundant and second, very fine-grained or forms rims on older (and much more abundant) hydrothermal calcite and is thus difficult to distinguish. Knowledge of chemical characteristics and the correlation with groundwater chemistry is thus scarce for low-temperature calcite in these settings, and consequently, knowledge of the recent palaeohydrogeological history is limited. Boreholes drilled with triple-tube technique in the upper 1 km of the Palaeoproterozoic crystalline crust at Laxemar, SE Sweden, have enabled preservation of fragile and potentially recently formed fracture minerals. Earlier investigations of these boreholes have resulted in an extensive set of groundwater chemistry data from various depths, and in detailed knowledge of the fracture mineral assemblages (ranging from 1.8 Ga to present). This has made it possible to identify and sample low-temperature, potentially recently formed, calcite from water-flowing fractures for which representative groundwater chemical data exists. This, in turn, provides an opportunity to detailed comparisons of fracture calcite (age span in the order of million years, with possibility of post-glacial contributes) and groundwater (age in the order of decades to more than a million year depending on depth) in terms of both isotopic and geochemical properties, giving input to the understanding of groundwater history, partition coefficients derived in laboratory experiment, and reliability of calcite geochemistry in terms of representing the actual source fluid composition. In this study, the focus is on trace elements (Fe, Mg, Mn and Sr), stable isotopes and Sr isotopes and, for the groundwater data set, also aquatic speciation with Visual MINTEQ. An optimised step-by-step sample specific analytical procedure was used for the collection of calcite coatings. The methods used depended on the crystal homogeneity (one or several calcite generations), discerned by detailed SEM-investigations (back-scatter and cathodo-luminescence). 87Sr/86Sr ratios as well as ?18O signatures in calcite are in the range expected for the precipitates from present-day groundwater, or older groundwater with similar composition (except in sections with a considerable portion of glacial water, where calcite definitely is older than the latest glaciation). Stable carbon isotopes in calcite generally show values typically associated with HCO3- originating from soil organic matter but at intermediate depth frequently with HCO3- originating from in situ microbial anaerobic oxidation of methane (highly depleted ?13C). For one of the studied metals - manganese - there was a strong correlation between the sampled calcite coatings and hypothetical calcite predicted by applying laboratory-based partition coefficients (literature data) on groundwater chemistry for sections corresponding to those where the calcites were sampled. This points to temporal and spatial stability in groundwater Mn/Ca ratios over millions of years, or even more, and show that it is possible to assess, based on laboratory-derived data on Mn partitioning, past groundwater Mn-composition from fracture calcites. For other metals - Fe, Sr, and Mg - which are expected to interact with co-precipitating minerals to a higher degree than Mn, the correlations between measured and predicted calcite were weaker for various reasons.

  17. Strontium incorporation into calcite generated by bacterial ureolysis

    NASA Astrophysics Data System (ADS)

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

    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 (D EX) 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.

  18. Benefits of a dual sagittal crystal transducer for ultrasound imaging during I-125 seed implantation for permanent prostate brachytherapy

    PubMed Central

    Pieters, Bradley; Koedooder, Kees; Lucas, Cees; Koning, Caro

    2012-01-01

    Purpose To investigate whether a longer sagittal view and less movement using a dual sagittal crystal probe (DSCP) for trans rectal ultra sound (TRUS) allow for more accurate online-planning in I-125 permanent implant brachytherapy of the prostate, compared to a single sagittal crystal probe (SSCP). Material and methods Between March 2008 and March 2010, 50 patients with prostate cancer were consecutively included in the study. The first 25 of these patients had both their pre- and online-planning based on a single sagittal crystal probe (SSCP). The treatment-plans of the other 25 patients were based on a DSCP TRUS. Three weeks after implantation a post-planning was made based on CT. TRUS online and CT post-plan dose-volume histogram (DVH) parameters, D90 and V100, were compared for both groups. Also, the post-plan DVH parameters of SSCP were compared to DSCP. The possible factors that might influence the post-plan D90 and V100 were analysed using Analysis of Variance (ANOVA). Results SSCP and DSCP online mean D90 and V100 were significantly larger than post-plan mean D90 and V100 (P < 0.01). The post-plan mean D90 and mean V100 were both non-significantly larger for SSCP based post-plans compared to DSCP based post plans (P = 0.76 and P = 0.68). ANOVA showed significant impact of prostate volume on the post-plan D90 and V100. Conclusions The advantages of the dual sagittal crystal probe did not lead to more accurate online planning by investigating DVH-parameters. The only factor found to have influence on the DVH-parameters was the prostate volume. PMID:23346143

  19. 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.

  20. Subaerial meteoric calcitization and lithification of high-magnesian calcite muds, Belize

    SciTech Connect

    Mazzullo, S.J.; Bischoff, W.D. (Wichita State Univ., KS (United States))

    1991-03-01

    Holocene ({lt}1000-1500 yrs old) high-magnesian calcite-dominated muddy sediments (1 m thick) on subaerially exposed cays in northern Belize are in the process of being converted to low-magnesian calcite micrite. Mineralogic stabilization and attendant lithification result from interaction of the sediments with meteoric fluids believed to be derived from seasonal upward discharge through subjacent Pleistocene limestones. The initial marine-derived sediments, composed of {gt}85% HMC (and minor skeletal aragonite), consist of mud and associated soritid and miliolid foraminifera both with MgCO{sub 3} content of 11-15 mol%, and isotopic compositions of -1.0 to -2.5{per thousand} PDB (O), 0 to +1.5{per thousand} PDB (C). With depth, lithified LMC crusts appear in the section, and the Mg concentration of the sediments and associated crusts decreases rapidly to 3 mol% or less, with a corresponding isotopic depletion to values approaching -7.0{per thousand} (O) and -5.8{per thousand} (C). Concomitantly there is progressive dissolution of skeletal aragonite in the sediments, reduction of porosity due to cementation by LMC, and in the muds, a decrease in Sr and increase in Mn contents. The resultant petrofabric of these lithified LMC deposits, derived from the alteration of HMC-dominated muds, is characterized by micrite with patches of pore-filling micritic and microsparitic LMC cements. Such a fabric is similar to and can be confused easily with calcitized aragonite-dominated precursor muds, except for the relative rarity in the samples examined of aragonite relicts in component microspar and/or pseudospar.

  1. Crystallization Pathways in Biomineralization

    NASA Astrophysics Data System (ADS)

    Weiner, Steve; Addadi, Lia

    2011-08-01

    A crystallization pathway describes the movement of ions from their source to the final product. Cells are intimately involved in biological crystallization pathways. In many pathways the cells utilize a unique strategy: They temporarily concentrate ions in intracellular membrane-bound vesicles in the form of a highly disordered solid phase. This phase is then transported to the final mineralization site, where it is destabilized and crystallizes. We present four case studies, each of which demonstrates specific aspects of biological crystallization pathways: seawater uptake by foraminifera, calcite spicule formation by sea urchin larvae, goethite formation in the teeth of limpets, and guanine crystal formation in fish skin and spider cuticles. Three representative crystallization pathways are described, and aspects of the different stages of crystallization are discussed. An in-depth understanding of these complex processes can lead to new ideas for synthetic crystallization processes of interest to materials science.

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

    Microsoft Academic Search

    Eurybiades Busenberg; L. Niel Plummer

    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

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

    E-print Network

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

    1977-07-22

    THE UNIVERSITY OF KANSAS 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...

  4. EXAFS study of rare-earth element coordination in calcite

    Microsoft Academic Search

    E. J. Elzinga; Richard Reeder; S. H. Withers; Robert E. Peale; R. A. Mason; Kenneth M. Beck; Wayne P. Hess

    2002-01-01

    Extended X-ray absorption fine-structure (EXAFS) spectroscopy is used to characterize the local coordination of selected rare-earth elements (Nd3+, Sm3+, Dy3+, Yb3+) coprecipitated with calcite in minor concentrations from room-temperature aqueous solutions. Fitting results confirm substitution in the Ca site, but first-shell Nd-O and Sm-O distances are longer than the Ca-O distance in calcite and longer than what is consistent with

  5. Kinetics and Mechanisms of Calcite Reactions with Saline Waters

    SciTech Connect

    Chapman, Piers; *Morse, John W. (*/deceased)

    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.

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

    SciTech Connect

    Zastrau, Ulf, E-mail: ulf.zastrau@uni-jena.de [Institute of Optics and Quantum Electronics, Friedrich-Schiller University Jena, Max-Wien-Platz 1, 07743 Jena (Germany); Stanford Linear Accelerator Center (SLAC), 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Fletcher, Luke B.; Galtier, Eric Ch.; Gamboa, Eliseo; Glenzer, Siegfried H.; Heimann, Philipp; Nagler, Bob; Schropp, Andreas; Lee, Hae Ja [Stanford Linear Accelerator Center (SLAC), 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Förster, Eckhart [Institute of Optics and Quantum Electronics, Friedrich-Schiller University Jena, Max-Wien-Platz 1, 07743 Jena (Germany); Helmholtz Institute Jena, Fröbelstieg 3, 07743 Jena (Germany); Marschner, Heike; Wehrhan, Ortrud [Institute of Optics and Quantum Electronics, Friedrich-Schiller University Jena, Max-Wien-Platz 1, 07743 Jena (Germany)

    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.

  7. 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 [Center for Micromagnetics and Information Technologies (MINT) and Department of Electrical and Computer Engineering, University of Minnesota, 200 Union St SE, 4-174 EE/CSci, Minneapolis, Minnesota 55455 (United States)

    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)].

  8. Seeding Rangeland. 

    E-print Network

    Welch, Tommy G.; Haferkamp, Marshall R.

    1987-01-01

    Co., Inc. Harpool Field Seed Inc. Horizon Seeds Sharp Bros. Seed Co. Tommy G. Welch and Marshall R. Haferkamp* Most Texas rangeland produces below its poten tial. Although production on some of this land may be improved by grazing management...

  9. Seawater pH control on the boron isotopic composition of calcite: evidence from inorganic calcite precipitation experiments

    Microsoft Academic Search

    A. Sanyal; M. Nugent; R. J. Reeder; J. Bijma

    2000-01-01

    Experiments involving boron co-precipitation with calcite have been carried out inorganically under controlled pH conditions (7.9 ± 0.05, 8.3 ± 0.05 and 8.6 ± 0.05) to determine the dependence of the boron isotopic composition (?11B) of calcite on the pH of seawater. Another purpose of these experiments was to estimate the magnitude of the biogenic influence on the ?11B value

  10. 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.

  11. The Thermodynamics Of Calcite Nucleation On Organic Surfaces: Classical Vs. Non-Classical Pathways

    NASA Astrophysics Data System (ADS)

    Nielsen, M.; Hu, Q.; Hamm, L. M.; Lee, J. R.; Becker, U.; Dove, P. M.; De Yoreo, J.

    2012-12-01

    Nucleation in the natural world often occurs at organic surfaces. During biomineralization, living organisms use macromolecular matrices to direct nucleation of a variety of inorganic materials by controlling the timing, polymorphism, morphology, and crystallographic orientation of mineral nuclei. In geochemical settings, mineral surfaces, which are often covered with organic layers or biofilms, surround the volume within which nucleation occurs. Despite the importance of nucleation phenomena in these natural settings, our understanding of the reaction dynamics and energetics of the process is limited. Issues such as the role of pre-nucleation clusters, formation of amorphous precursors, and polymorph selection during the initial stages of nucleation, as well as the structural relationships between the organic matrix and the emerging nucleus are poorly understood. Using self-assembled monolayers (SAMs) of alkanethiols as simple models for macromolecular matrices and organic films, we address the gaps in our understanding by employing a suite of in situ methods to investigate CaCO3 nucleation. From optical measurements of calcite nucleation rates on alkanethiol SAMs, we find that for two carboxyl-terminated alkanethiol SAMs with odd (mercaptoundecanoic acid) and even (mercaptohexadecanoic acid) carbon chains, the rate exhibits the supersaturation dependence expected from classical theory and the effective interfacial energy is reduced from about 109 mJ/m2 in bulk solution to 81 mJ/m2 and 72 mJ/m2, respectively. Theoretical analysis shows that the corresponding free energy barrier is reduced from 105kT for homogeneous nucleation in bulk solution to 27KT and 19kT, respectively. The results demonstrate that calcite nucleation on these carboxyl SAMs is described well in purely classical terms through a reduction in the thermodynamic barrier due to decreased interfacial free energy. In addition, although amorphous particles form prior to crystal nucleation on hydroxyl SAMs and during crystal nucleation on carboxyl SAMs — even well below the accepted bulk solubility limit for amorphous calcium carbonate (ACC) — they do not grow and are not precursors to the crystalline phase. Instead, calcite nucleates independently. These results call into question the emerging view of calcite nucleation as a non-classical process. Finally we show how questions concerning formation pathways and energetic controls of templated nucleation can be investigated with in situ transmission electron microscopy (TEM) at nanometer scale and video rates. This capability is enabled by the combination of a custom designed TEM stage and fluid cell. Significantly, the design of the cell and holder ensures temperature and electrochemical control over the reaction environment, allowing for direct investigation of nucleation dynamics.

  12. 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: cedric.carteret@univ-lorraine.fr, E-mail: marco.delapierre@unito.it; Maschio, Lorenzo; Orlando, Roberto; Dovesi, Roberto [Dipartimento di Chimica, Università di Torino and NIS (Nanostructured Interfaces and Surfaces) Centre of Excellence, Via P. Giuria 7, 10125 Torino (Italy)] [Dipartimento di Chimica, Università di Torino and NIS (Nanostructured Interfaces and Surfaces) Centre of Excellence, Via P. Giuria 7, 10125 Torino (Italy); Carteret, Cédric, E-mail: cedric.carteret@univ-lorraine.fr, E-mail: marco.delapierre@unito.it; André, Erwan [Laboratoire de Chimie Physique et Microbiologie pour l’Environnement (LCPME), UMR 7564, Université de Lorraine-CNRS, 405 rue de Vandoeuvre, 54601 Villers-lès-Nancy (France)] [Laboratoire de Chimie Physique et Microbiologie pour l’Environnement (LCPME), UMR 7564, Université de Lorraine-CNRS, 405 rue de Vandoeuvre, 54601 Villers-lès-Nancy (France)

    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.

  13. Shock Vaporization of Anhydrite and Calcite and the Effect on Global Climate from K/T Impact Crater at Chicxulub

    NASA Astrophysics Data System (ADS)

    Yang, W.; Ahrens, T. J.; Chen, G.

    1996-03-01

    The dominance of calcium sulfate minerals (anhydrite and gypsum) and calcium carbonate (calcite) in the upper 3 km of the Chicxulub section has prompted active research on the effects of their devolatilization upon impact. We present new data of vaporization criteria for anhydrite and calcite, the amount of S and C degassed during the Chicxulub impact and their effects on the global climate based on shock wave experiments, numerical simulation and thermodynamic calculations. The incipient and complete vaporization pressures are 81 +/- 7 GPa and 155 +/- 13 GPa for crystal anhydrite and the incipient and complete vaporization pressures are 54 +/- 6 GPa and 103 +/- 12 GPa for calcite crystal. About 3-20 x 10^16 gm carbon and 4-36 x 10^16 gm sulfur were degassed into the atmosphere due to the Chicxulub bolide. The global warming caused by the degassed CO2 is 0.2 degrees - 1.1 degrees C and the global cooling introduced by the degassed SO2 is 8.5 degrees - 16 degrees C.

  14. crystals

    NASA Astrophysics Data System (ADS)

    Badalyan, A.; Hovsepyan, R.; Mantashyan, P.; Mekhitaryan, V.; Drampyan, R.

    2014-07-01

    A novel combined interferometric-mask method for the formation of micro- and nanometric scale three-dimensional (3D) rotational symmetry quasi-crystalline refractive lattice structures in photorefractive materials is demonstrated experimentally. The method is based on micrometric scale spatial modulation of the light by amplitude mask in the radial directions and along the azimuthal angle and the use of counter-propagating beam geometry building up Gaussian standing wave, which defines the light modulation in the axial direction with half-wavelength periodicity. 3D intensity pattern can be represented as numerous mask-generated 2D quasi-periodic structures located in each anti-node of the standing wave. The formed 3D intensity distributions of the optical beams can be imparted into the photorefractive medium thus creating the micro- and sub-micrometric scale 3D refractive index volume lattices. The used optical scheme allows also the formation of 2D lattices by removing the back-reflecting mirror. 2D and 3D refractive lattices were recorded with the use of 532 nm laser beam and rotational symmetry mask in doped lithium niobate crystals and were tested by the probe beam far-field diffraction pattern imaging and direct observation by phase microscope. The formed rotational symmetry 3D refractive structures have the periods of 20-60 ?m in the radial directions, 60 ?m along the azimuthal angle and half-wavelength 266 nm in the axial direction.

  15. Clumped isotope paleothermometry of marine calcite cements from the Late Ordovician Kullsberg and Boda Limestones, Sweden

    NASA Astrophysics Data System (ADS)

    Finnegan, S.; Eiler, J. M.; Fischer, W. W.

    2012-12-01

    18O/16O ratios (?18O) in well-preserved marine carbonates provide a critical archive of information about ancient climates and seawater chemistry, but this proxy suffers from a fundamental limitation. Because ?18O reflects a temperature-dependent equilibrium fractionation between the measured mineral and the water with which it equilibrated, neither the temperature nor the isotopic composition of this water (?18Owater) can be determined directly from ?18O of carbonate without independent knowledge of one of the controlling variables. Lack of such knowledge has been the major factor preventing resolution of a long-running debate over the interpretation of secular trends in ?18O. Clumped isotope paleothermometry is a recently developed thermodynamic proxy that permits independent determination of carbonate crystallization temperature and can place unique constraints on ?18Owater. Most clumped isotope analyses have focused on calcitic fossils, but marine calcite cements are common in carbonate-rich successions and provide a complementary archive that may shed light on both primary temperature trends and their diagenetic alteration. We examined the clumped isotope systematics of samples from the Late Ordovician Kullsberg and Boda Limestones of central Sweden. These units have never been substantially buried but may have affected by the nearby Siljan impact of Late Devonian age. Both were deposited at tropical to low subtropical latitudes and contain large micritic buildups rich in "stromatactis" voids containing multiple cement generations. Previous work (Tobin and Walker, 1996) characterized the Kullsberg cements and posited that translucent fibrous calcites record unaltered to slightly altered marine signatures and turbid fibrous calcites record variable alteration by restricted marine fluids, with subsequent generations of equant calcite recording meteoric and/or burial fluids. Translucent and turbid fibrous calcite in the Kullsberg exhibit narrow ?18O ranges (-2.2 to -4.5‰ VPDB) but significant variations in temperature (31° to 51°C), implying partially closed system diagenetic behavior. Many samples capture physical mixtures of relatively primary phases with 18O-depleted, high temperature meteoric or burial phases (mean ?18O = -8.1 ± 0.7‰ VPDB, mean temp. = 58 ± 3° C). Boda cements record generally higher temperatures, consistent with other evidence suggesting that the Boda has experienced more diagenetic alteration. Consequently, we interpret the lowest-temperature Kullsberg samples as most likely to record a primary marine signature. Samples yielding temperatures <35°C exhibit ?18Owater values from 0.94 to -0.14‰ VSMOW. Minimum ?18Owater values inferred from these sampled are indistinguishable from those inferred from well preserved calcitic fossils from the contemporaneous Decorah Formation of the U.S. midcontinent that record lighter ?18O values and higher temperatures. This suggests that both least-altered Kullsberg cements and Decorah Formation fossils were sampling isotopically similar seawater in the 0 to -1‰ VSMOW range but precipitated at different temperatures, an observation consistent with their relative latitudinal positions.

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

    SciTech Connect

    DePaolo, Donald J. [Lawrence Berkeley Nat'l Lab. (LBNL), Berkeley, CA (United States)

    2011-02-01

    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 (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} ? 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} ? 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 require hyper-fast diffusivity in near-surface layers of the solid.

  17. 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

  18. Nuclear anomalies in the buccal cells of calcite factory workers

    PubMed Central

    2010-01-01

    The micronucleus (MN) assay on exfoliated buccal cells is a useful and minimally invasive method for monitoring genetic damage in humans. To determine the genotoxic effects of calcite dust that forms during processing, MN assay was carried out in exfoliated buccal cells of 50 (25 smokers and 25 non-smokers) calcite factory workers and 50 (25 smokers and 25 non-smokers) age- and sex-matched control subjects. Frequencies of nuclear abnormalities (NA) other than micronuclei, such as binucleates, karyorrhexis, karyolysis and ‘broken eggs', were also evaluated. Micronuclei and the other aforementioned anomalies were analysed by two way analysis of covariance. The linear correlations between the types of micronucleus and nuclear abnormalities were determined by Spearman's Rho. There was a positive correlation between micronuclei and other types of nuclear abnormalities in accordance with the Spearman's Rho test. Results showed statistically significant difference between calcite fabric workers and control groups. MN and NA frequencies in calcite fabric workers were significantly higher than those in control groups (p < 0.05). The results of this study indicate that calcite fabric workers are under risk of significant cytogenetic damage. PMID:21637497

  19. Seed Germination

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Initiation of seed germination is a critical decision for plants. It is important for seed populations under natural conditions to spread the timing of germination of individual seeds to maximize the probability of species survival. Therefore, seeds have evolved the multiple layers of mechanisms tha...

  20. Heat-Exchanger Method of Crystal Growth

    NASA Technical Reports Server (NTRS)

    Khattak, C. P.; Schmid, F.

    1982-01-01

    Large crystals of silicon are grown from melt, in either vacuum or pressurized atmosphere, without moving crucible, furnace, or anything else. Seed crystal is mounted on helium-cooled heat exchanger, which prevents seed from melting when furnace melts rest of silicon material in crucible; heat exchanger draws off heat from melt so that a solid ingot grows outward from seed in a regular crystal structure. Bottom of crucible is insulated so that heat exchanger cools only seed.

  1. 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.

  2. Magnesium incorporation in calcite in the presence of organic ligands

    NASA Astrophysics Data System (ADS)

    Mavromatis, Vasileios; Baldermann, Andre; Purgstaller, Bettina; Dietzel, Martin

    2015-04-01

    The formation of authigenic Mg-calcites in marine early diagenetic environments is commonly driven by a bio-induced process, the anaerobic oxidation of methane (AOM), which provides inorganic carbon required for the precipitation of such authigenic carbonates. In such settings the availability of major and/or trace divalent metal cations (Me2+) incorporated in calcite and their aqueous speciation are controlled by the presence of aqueous organic molecules that are produced either as (by-)products of biological activity (i.e. exopolymeric substances) or during degradation of allochthonous organic matter in the sediments. Despite the fact that the presence of aqueous organic ligands strongly affects the growth rates and the mineralogy of precipitating CaCO3 polymorphs, till now no study addresses the role of Me2+-ligand aqueous complexes on the extent of Mg and/or other trace element content of Mg-calcites. In order to shed light on this process, relevant to authigenic calcite formation in organic-rich marine sediments and continental soils, we precipitated calcite in the presence of aqueous Mg and a variety of low molecular weight carboxylic- and aminoacids. Our experimental data indicate that the presence of organic ligands augments significantly the saturation state of calcite in the parent fluid during its precipitation. Moreover, they suggest that the higher the ligand concentration, the higher the obtained distribution coefficient of Mg in calcite. The latter is directly proportional to the ratio of Mg2+/Ca2+ aqueous ions for all ligands used. Hydrogeochemical modelling of the aqueous fluids indicate that the observed correlation can be explained by the stronger complexation of Ca2+ with organic ligands compared to Mg2+, which results in higher availability of Mg2+ vs. Ca2+ aqueous ions. Overall the obtained results suggest that the higher the organic ligand aqueous concentration the higher the Mg content of calcite forming from this fluid. These findings are of great importance for the understanding of the mechanisms controlling impurities and trace element incorporation in carbonates forming in marine diagenetic and soil environments.

  3. Siderite and calcite in lignite overburden of East Texas 

    E-print Network

    Durham, David Hugh

    1982-01-01

    ) of carbonate v4 mode of absozbance versus cation radius (A) in cal- cite type carbonates 10 Fig. 3--X-ray diffraction dlO4 carbonate spacing (A) versus cation radius (A) in calcite type carbonates Fig. 4--Locations of cores that were selected foz carbonate.... 26 ? Infrared spectoscopy data for the region from 760 cm to 700 cm 1 148 INTRODUCTION The common carbonate minerals, calcite, dolomite, and magnesite, can neutralize acidity of soil and supply a basic cation to the cation exchange complex upon...

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

    SciTech Connect

    Slunder, J.S. (EMPE Inc., Nashville, TN (United States)); Groves, C.G. (Western Kentucky Univ., Bowling Green, KY (United States). 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.

  5. 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.

  6. 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.

  7. 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.

  8. Production of Calcite by the Green Alga Halimeda in Artificial Cretaceous Seawater

    NASA Astrophysics Data System (ADS)

    Stanley, S. M.; Ries, J. B.

    2006-12-01

    The codiacean green alga Halimeda contributes 20-30% of the carbonate sediment in lagoonal areas adjacent to modern Caribbean and Indo-Pacific coral reefs. This alga is syncytial, lacking cell membranes, so that an individual thallus functions as a giant, multinucleate cell. The thallus grows as branching chains of segments interconnected by tubular filaments. A segment is formed in a single day and then filled with calcium carbonate over several days. Aragonite crystals grow within segments in the form of needles, but in some regions of a segment these are subsequently dissolved and their calcium carbonate is reprecipitated as microgranular aragonite. Some of the needles grow in a spherulitic pattern similar to that of inorganic aragonite precipitates. It has been debated whether Halimeda employs organic templates to secrete the aragonite polymorph of calcium carbonate or simply induces precipitation by taking up carbon dioxide for photosynthesis. We have found that Halimeda incrassata segments grown in seawater of modern ionic composition (Mg/Ca molar ratio = 5.2) actually contain an average of about 8% high-Mg calcite (mean 16 mol % Mg substituting for Ca). As the Mg/Ca ratio of ambient seawater is stepped down, calcite constitutes an increasing percentage of the calcium carbonate produced, and, as we have found for numerous other kinds of organisms, the Mg content of the calcite declines. For segments grown in seawater with the imputed Cretaceous Mg/Ca molar ratio of 1.5, calcite constituted, on average, 46% of the calcium carbonate (maximum, 67%) and contained about 6 mol% Mg. Experiments show that in artificial seawaters having different Mg/Ca molar ratios but otherwise having the ionic strength and chemical composition of modern seawater, aragonite can precipitate inorganically when the Mg/Ca molar ratio is above 2. The fact that Halimeda produces slightly more aragonite than calcite when the ambient Mg/Ca molar ratio is 1.5 indicates that it does exert a degree of biological control over its calcium carbonate production, but that the control is incomplete. Our growth experiments showed that there is a correlation between rate of production of carbonate and rate of production of organic matter by Halimeda, apparently because, as has been previously demonstrated, this alga's photosynthesis is enhanced by the carbon dioxide produced by its calcification. Productivity was highest in seawater of modern composition. Experiments in which either the ambient Mg/Ca ratio or the absolute concentration of Ca was held constant while the other was varied showed that an increase in either one led to a higher rate of production of both organic matter and calcium carbonate. Nonetheless, rates of production were higher in imputed Cretaceous seawater (Mg/Ca molar ratio = 1.5) than in imputed Oligocene seawater (Mg/Ca molar ratio = 2.5), presumably because in the Oligocene treatment, both of the minerals produced (high-Mg calcite and aragonite) were favored by the ambient Mg/Ca ratio, whereas in the Cretaceous treatment, 56% of the calcium carbonate was aragonite, which was not favored by the ambient Mg/Ca ratio.

  9. Narrow-bandwidth, mid-infrared, seeded optical parametric generation in 90° phase-matched CdSiP2 crystal pumped by diffraction limited 500 ps pulses at 1064 nm.

    PubMed

    Marchev, Georgi; Pirzio, Federico; Piccoli, Riccardo; Agnesi, Antonio; Reali, Giancarlo; Schunemann, Peter G; Zawilski, Kevin T; Tyazhev, Aleksey; Petrov, Valentin

    2012-08-01

    Low-threshold, efficient optical parametric generation at ~6100 nm is demonstrated using CdSiP2 nonlinear crystal at 1 to 10 kHz repetition rates with relatively long 500 ps pump pulses at 1064 nm. Maximum single pulse energy of 8.7 ?J and average power of 79 mW are achieved for the idler. Seeding at the signal wavelength is employed using a distributed feedback laser diode, which enables approximately tenfold narrowing of the idler bandwidth down to less than 1 nm. PMID:22859138

  10. Inter-relations entre aiguilles de calcite et hyphes Gabriel CALLOT, Andr GUYON Daniel MOUSAIN

    E-print Network

    Paris-Sud XI, Université de

    Inter-relations entre aiguilles de calcite et hyphes mycéliens Gabriel CALLOT, André GUYON Daniel'intérieur des hyphes de Basidiomycètes. Ces concentrations minérales s'identifient aux aiguilles de calcite

  11. "EXAFS Study of Rare-Earth Element Coordination in Calcite"

    SciTech Connect

    Elzinga, E. J.; Reeder, Richard; Withers, S. H.; Peale, Robert E.; Mason, R. A.; Beck, Kenneth M.; Hess, Wayne P.

    2002-03-11

    X-ray absorption fine-structure (XAFS) spectroscopy is used to characterize the local coordination of selected rare-earth elements (Nd3+, Sm3+, Dy3+, Yb3+) coprecipitated with calcite in minor concentrations from room-temperature aqueous solutions. Fitting results confirm substitution in the Ca site, but first-shell Nd-O and Sm-O distances are longer than the Ca-O distance in calcite, and longer than consistent with ionic radii sums for 6-fold coordination in the octahedral Ca site. In contrast, first-shell Dy-O and Yb-O distances are shorter than the Ca-O distance and consistent with ionic radii sums for 6-fold coordination. Comparison of Nd-O and Sm-O bond lengths with those in lanthanide sesquioxides and with ionic radii trends across the lanthanide series suggested that Nd3+ and Sm3+ impurities have 7-fold coordination in a modified Ca site in calcite. This would require some disruption of the local structure, with an expected decrease in stability and possibly a different charge compensation mechanism. A possible explanation for the increased coordination for the larger rare earth elements involves bidenate ligation from a CO3 group. Because trivalent actinides such as Am3+ and Cm3+ have ionic radii similar to Nd3+, their incorporation in calcite may result in similar defect structure.

  12. Aragonite / Calcite seas and the evolution of biomineralization

    NASA Astrophysics Data System (ADS)

    Balthasar, Uwe

    2015-04-01

    The vast majority of marine invertebrate skeletons are composed of the CaCO3 polymorphs aragonite and calcite, yet the influence of seawater composition on the evolution of calcareous skeletal composition is poorly understood. The main theoretical framework in which the evolution of CaCO3 shell mineralogy is assessed is the aragonite-calcite sea hypothesis with conventional thinking suggesting that a threshold in the marine Mg:Ca ratio determines CaCO3 polymorph formation. I present data from CaCO3 precipitation experiments to show that the concept of a distinct threshold is misleading because Mg:Ca ratio and temperature combined result in a Phanerozoic continuum of co-existing aragonite-calcite seas with aragonite-facilitating conditions existing throughout the Phanerozoic in shallow warm-water (>20° C) environments. The stable reservoir of aragonite-favouring conditions in shallow warm water environments potentially explains the trend of increasing occurrences of skeletal aragonite throughout the Phanerozoic, particularly in the context of the 'out of the tropics' hypothesis. By contrast, the most prominent fluctuations with respect to aragonite-calcite sea conditions can be expected to have occurred in mid- to high latitudes.

  13. X-ray line broadening in plastically deformed calcite

    Microsoft Academic Search

    M. S. Paterson

    1959-01-01

    The broadening of several x-ray powder lines of calcite as a result of plastic deformation under a high confining pressure has been studied in Solenhofen limestone. The dependence of the broadening on the Bragg engle, the apparent influence of elastic anisotropy and the results of Fourier analysis of the lines suggest that the broadening is due mainly ta internal strains.

  14. Experimentelle Bildung von Forsterit und Calcit aus Tremolit und Dolomit

    Microsoft Academic Search

    Paul Metz

    1967-01-01

    The equilibrium temperature for the reaction: 1 tremolite + 11 dolomite 8 forsterite + 13 Calcit + 9 CO 2 + 1 H 2 O was experimentally determined as a function of the CO 2 -content of the CO 2 -H 2 O fluid phase for the total pressures of 500 and 1000 bars. The results are plotted as two

  15. Quantitative estimation of calcite in limestones by differential thermal analysis

    Microsoft Academic Search

    K. Jehan; M. A. Qaiser; A. H. Khan

    1972-01-01

    A quantitative method is presented for the estimation of calcite in limestones by differential thermal analysis, using calcium hydroxide as an internal standard. The effects of variations due to particle size and impurities such as quartz, iron oxide, organic material, dolomite, magnesite, gypsum and phosphates are discussed.

  16. An experimental study of strontium and lead diffusion in calcite, and implications for carbonate diagenesis and metamorphism

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.

    1997-10-01

    Chemical diffusion of Pb and Sr has been measured in natural calcite under anhydrous conditions. The source of diffusants for the Sr and Pb diffusion experiments were SrCO 3 and PbO powders, respectively. Experiments were run in sealed silica capsules containing finely ground calcite to ensure stability of the single-crystal samples during diffusion anneals. Rutherford backscattering spectroscopy (RBS) was used to measure diffusion profiles. The following Arrhenius relations were obtained over the temperature range 440-800°C for Sr, 440-650° for Pb: D Sr = 2.1 x 10 -13exp(-132 ± 6 kJ mol -1/RT) m 2 s -1D Pb = 5.8 x 10 -15exp(-117 ± 9 kJ mol -1/RT) m 2 s -1 Diffusion of Sr and Pb is relatively rapid in comparison to rates for these elements in other minerals, but fine-scale zoning and isotopic and chemical signatures many be retained in calcites under many conditions if diffusion is the dominant process affecting alteration.

  17. 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.

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

    NASA Astrophysics Data System (ADS)

    Henkes, Gregory A.; Passey, Benjamin H.; Grossman, Ethan L.; Shenton, Brock J.; Pérez-Huerta, Alberto; Yancey, Thomas E.

    2014-08-01

    Solid-state reordering of C-O bonds in the calcite lattice can alter the clumped isotope composition of paleotemperature archives such as fossil brachiopod shells without inducing significant changes in shell microstructure and trace element concentrations, metrics commonly used to gauge preservation quality. To correctly interpret the paleoenvironmental significance of clumped isotope-derived paleotemperatures, it is necessary to understand the temperature-time domain in which solid-state C-O bond reordering is important. We address this question using a combination of laboratory and natural geological experiments on Paleozoic brachiopod shells. The laboratory experiments involve heating fossil brachiopod calcite at different temperatures and times to directly observe rates of 13C-18O bond reordering. The resulting Arrhenius parameters are indistinguishable from values previously determined for an optical calcite with similar trace element compositions. We develop an alternative kinetic model for reordering that accounts for non-first-order reaction progress observed during the initial several hundred minutes of laboratory heating experiments, and show that the simplified first-order approximation model (Passey and Henkes, 2012) predicts reaction progress equally well for temperatures and timescales relevant to sedimentary basins. We evaluate our laboratory-based rate predictions by studying brachiopod calcite from several sedimentary basins with independently constrained burial temperature histories. Specifically, we use the laboratory-derived Arrhenius parameters to predict the evolution of brachiopod calcite clumped isotope compositions during successive one million-year time steps reflecting the burial and exhumation temperature paths of each basin. While this exercise is limited by the relatively large uncertainties in the temperature histories of these basins, we find general correspondence, within error, between predicted and observed clumped isotope values. We present simplified temperature-time diagrams for calcite showing domains where primary clumped isotope compositions will be preserved, partially reordered, and fully reordered. In conclusion, calcite samples dwelling at ?100 °C or lower for 106-108 year timescales should not be affected by solid-state C-O bond reordering.

  19. 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.

  20. High Birefringence Isothiocyanato Tolane Liquid Crystals Sebastian GAUZA, Haiying WANG, Chien-Hui WEN, Shin-Tson WU, Alexander J. SEED1

    E-print Network

    Wu, Shin-Tson

    High Birefringence Isothiocyanato Tolane Liquid Crystals Sebastian GAUZA, Haiying WANG, Chien temperatures, birefringence and visco-elastic coefficient of several high birefringence isothiocyanato tolane: High birefringence, isothiocyanato tolanes, liquid crystals, polarizability 1. Introduction High

  1. Seeding Rangeland 

    E-print Network

    Welch, Tommy G.; Hafercamp, Marshall R.

    2001-01-04

    Most Texas rangeland produces below its potential. Improving rangeland requires brush control and/or seeding to restore production to the site's potential. This publication is a guide to seeding rangelands, and discusses ...

  2. 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

  3. Seed Dispersal

    NSDL National Science Digital Library

    2012-06-26

    In this outdoor activity and bingo-like game, learners explore why and how seeds spread far from the plants that produce them. To understand natural adaptions that let seeds and fruit be dispersed, learners make modifications to dried beans and peas so they could be dispersed by natural forces like water, air, or an animal moving from one place to another. In the "Seed-Go" Game, learners match ways that seeds are dispersed, to fill rows on the game board.

  4. “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...

  5. Structure and properties of Bi(Zn0.5Ti0.5)O3- Pb(Zr1-?Ti?)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(Zr1-?Ti?)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 TC 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 EC of 22.1 kV/cm. PMID:26067036

  6. Fluid inclusion evidence for origin and diagenesis of sparry calcite cement in Capitan Limestone, McKittrick Canyon, Permian basin, west Texas

    Microsoft Academic Search

    Bonnie L. Crysdale

    1986-01-01

    Sparry calcite cement is responsible for major porosity loss in the reef and fore-reef facies of the Capitan Limestone, Permian basin. This cement occurs throughout the massive reef facies where it fills large vugs as much as 0.5 m in diameter, with individual crystals up to several centimeters in length. Sparry cement in the fore-reef facies is less extensive and

  7. 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)

  8. Phosphoprotein modulation of apatite crystallization

    Microsoft Academic Search

    J. D. Termine; E. D. Eanes; K. M. Conn

    1980-01-01

    Summary  Several phosphoprotein preparations (phosvitin, rat incisor and fetal calf molar dentin phosphoproteins) all inhibit apatite\\u000a growth\\/replication from pre-existing crystal seeds in metastable solutions. Two stages of the crystal growth process were\\u000a inhibited by these phosphoproteins. First, an initial lag period was induced, probably associated with seed surface phenomena.\\u000a This period was prolonged indefinitely when a combination of phosphoprotein precoated seeds

  9. Effect of trace lanthanum ion on dissolution and crystal growth of calcium carbonate

    NASA Astrophysics Data System (ADS)

    Kamiya, Natsumi; Kagi, Hiroyuki; Tsunomori, Fumiaki; Tsuno, Hiroshi; Notsu, Kenji

    2004-07-01

    Impurity effects of trace lanthanum ion (La 3+) on the dissolution and growth of calcium carbonate were studied with in situ observation techniques. Dissolution kinetics of two polymorphs of calcium carbonate, calcite and vaterite, were investigated by monitoring the pH in the solution with laser-induced fluorescence spectroscopy using a pH-sensitive reagent, seminaphthorhodafluors. No effect on dissolution of vaterite was observed with the spectroscopic observations, whereas calcite dissolution was significantly inhibited by lanthanum ion with concentrations higher than 1 ?M. Crystal growth and dissolution processes of calcite under the lanthanum-doped condition were observed by means of atomic force microscopy. Step propagations during crystal growth and dissolution of calcite were inhibited by trace lanthanum ion (5 ?M). An insoluble thin layer of lanthanum carbonate deposited on the step site of the calcite surface could be a possible cause of the inhibitions observed both for dissolution and growth.

  10. Humidity-induced restructuring of the calcite surface and the effect of divalent heavy metals.

    PubMed

    Hausner, Douglas B; Reeder, Richard J; Strongin, Daniel R

    2007-01-01

    The composition and topography of calcite 10114 cleavage surfaces, with and without exposure to divalent metals, have been investigated as a function of relative humidity. Atomic force microscopy (AFM) was used to understand topographical changes on the calcite surface due to the presence of divalent metal and exposure to different humid environments. Ion scattering spectroscopy (ISS) was used to determine the composition of the near and outermost surface of the calcite after exposure to Cd and Pb and before exposure to the varying humidity conditions. In general, the extent of topographical changes observed on the calcite surface increased with the humidity level, though the initial step density of the cleaved calcite surface affects the extent of surface restructuring. Pretreatment of the calcite surface with aqueous divalent Pb prior to humidity exposure did not appear to alter the humidity-induced structural changes that occurred on the calcite surface. In contrast, calcite pretreated with divalent Cd showed little topographical change following exposure to high humidity. The results suggest that while Pb forms surface precipitates on the calcite surface, Cd exhibits a stronger interaction with the step edges of the calcite surface, which inhibits the ability of the calcite surface to restructure when exposed to a high relative humidity environment. PMID:17052725

  11. 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.

  12. 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.

  13. Oxygen isotope fractionation in quartz, albite, anorthite and calcite

    SciTech Connect

    Clayton, R.N.; Goldsmith, J.R.; Mayeda, Toshiko K. (Univ. of Chicago, IL (USA))

    1989-03-01

    Laboratory measurements of equilibrium oxygen isotope fractionation in quartz, albite, anorthite, and calcite have been carried out by anhydrous exchange between silicates and calcite at temperatures of 600{degree}C and above. Exchange in these systems is as rapid as exchange between silicates and water. In this paper results are compared with published theoretical estimates as well as data derived from hydrothermal experiments. Some significant differences are found. In particular, it is difficult to reconcile all of the hydrothermal data either with theoretical calculations or with the present experimental data. The new experiments provide an internally consistent set of fractionation factors suitable for isotopic thermometry and for test of disequilibrium in natural systems.

  14. 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.

  15. Relating Mechanical Behavior and Microstructural Observations in Calcite Fault Gouge

    NASA Astrophysics Data System (ADS)

    Carpenter, B. M.; Di Stefano, G.; Viti, C.; Collettini, C.

    2013-12-01

    Many important earthquakes, magnitude 5-7, nucleate and/or propagate through carbonate-dominated lithologies. Additionally, the presence of precipitated calcite in (cement) and near (vein fill) faults indicates that the mechanical behavior of carbonate-dominated material likely plays an important role in shallow- and mid-crustal faulting. We report on laboratory experiments designed to explore the mechanical behavior of calcite and relate that behavior to post experiment microstructural observations. We sheared powdered gouge of Carrara Marble, >98% CaCO3, at constant normal stresses between 1 and 50 MPa under saturated conditions at room temperature. We performed velocity-stepping tests, 0.1-1000 ?m/s, to evaluate frictional stability, and slide-hold-slide tests, 1-10,000 seconds, to measure the amount of frictional healing. Small subsets of experiments were performed under different environmental conditions and shearing velocities to better elucidate physicochemical processes and their role in the mechanical behavior of calcite fault gouge. All experimental samples were collected for SEM analysis. We find that the frictional healing rate is 7X higher under saturated conditions than under nominally dry conditions. We also observe a divergence between the rates of creep relaxation (increasing) and frictional healing (decreasing) as shear velocity is increased from 1 to 3000 ?m/s. Our highest healing rates are observed at our lowest normal stresses. We observe a frictional strength of ? = 0.64, consistent with previous data under similar conditions. Furthermore, although we observe velocity-weakening frictional behavior in both the saturated and dry cases, rate- and-state friction parameters are distinctly different for each case. Our combined observations of rapid healing and of velocity-weakening frictional behavior indicate that faults where calcite-dominated gouge is present are likely to be seismic and have the ability to regain their strength quickly. Furthermore, our mechanical results highlight the important role of fluids in the evolution of frictional strength and thus fault behavior.

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

    SciTech Connect

    Nagy, K.L.; Cygan, R.T.; Brinker, C.J.; Ashley, C.S. [Sandia National Labs., Albuquerque, NM (United States); Scotto, C.S. [Naval Research Lab., Washington, DC (United States). Optical Sciences Div.

    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.

  17. A re-evaluation of aragonite versus calcite seas

    Microsoft Academic Search

    Mohammad H. Adabi

    2004-01-01

    Some workers have argued that the mineralogy of ancient carbonates may have been different from that of modern sediments,\\u000a with calcite being considered the dominant mineral during the Ordovician, Devonian-mid Carboniferous, and Jurassic-Cretaceous\\u000a to Early\\/Middle Cenozoic (e.g. Sandberg 1983; Wilkinson and Algeo 1989). Variation in carbonate mineralogy has been related\\u000a to the position of global sea level (emergent or submergent

  18. Gehlenite and anorthite crystallisation from kaolinite and calcite mix

    Microsoft Academic Search

    Karfa Traoré; Tibo Siméon Kabré; Philippe Blanchart

    2003-01-01

    Clay products can be reinforced by using clay and calcite mixes, even if sintering is at low temperature (1100 °C). The formation of a micro-composite microstructure favours a significant strength increase as fired materials contain anorthite grains embedded in a silico-aluminate matrix. The clay used, rich in kaolinite mineral, is originated from Burkina-Faso. It is contaminated by a moderate iron level,

  19. Cosmogenic Chlorine36 Production in Calcite by Muons

    Microsoft Academic Search

    J. O. H. Stone; J. M. Evans; L. K. Fifield; G. L. Allan; R. G. Cresswell

    1998-01-01

    At depths below a few metres, 36Cl production in calcite is initiated almost entirely by cosmic ray muons. The principal reactions are (1) direct negative muon capture by Ca; 40Ca(??,?)36Cl, and (2) capture by 35Cl of secondary neutrons produced in muon capture and muon-induced photodisintegration reactions. We have determined rates for 36Cl and neutron production due to muon capture in

  20. Magnesium stable isotope fractionation in marine biogenic calcite and aragonite

    Microsoft Academic Search

    F. Wombacher; A. Eisenhauer; F. Böhm; N. Gussone; M. Regenberg; W.-Chr. Dullo; A. Rüggeberg

    2011-01-01

    This survey of magnesium stable isotope compositions in marine biogenic aragonite and calcite includes samples from corals, sclerosponges, benthic porcelaneous and planktonic perforate foraminifera, coccolith oozes, red algae, and an echinoid and brachiopod test. The analyses were carried out using MC-ICP-MS with an external repeatability of ±0.22‰ (2SD for ?26Mg; n=37), obtained from a coral reference sample (JCp-1).Magnesium isotope fractionation

  1. Calcite and dolomite discrimination using airborne SWIR imaging spectrometer data

    Microsoft Academic Search

    Neil Rowlands; Robert A. Neville

    1996-01-01

    The SWIR full spectrum imager (SFSI) is a hyperspectral push-broom imager, acquiring imagery in 120 0.010 micrometers wide bands simultaneously covering the 1.20 micrometers to 2.47 micrometers spectral region. During the first flights of the instrument hyperspectral imagery was acquired over a calcite quarry and a dolomite quarry. Both these minerals show distinctive carbonate absorption features in the 1.7 to

  2. The kinetics of microstructural evolution during deformation of calcite

    NASA Astrophysics Data System (ADS)

    Austin, Nicholas; Evans, Brian

    2009-09-01

    There is a strong coupling between the microstructure and the strength of rocks that is thought to play a key role in the evolution of shear zones and in our ability to interpret the mechanics of natural deformation processes. To investigate the microstructural evolution of calcite-rich rocks, we have performed a series of hydrostatic and deformation experiments on synthetic calcite aggregates at 1023 K and 300 MPa. The mechanical data from our experiments were broadly consistent with a composite flow law for concurrent dislocation and diffusion creep. Recrystallization rates responded to the deformation conditions. When the bulk strain rate was dominated by diffusion creep, calcite grains grew at the same rate as occurs by normal grain growth under isostatic conditions. When the dominant deformation mechanism was dislocation creep, the matrix grain size was reduced at a rate that varied directly with product of stress, strain rate, and the square of grain size. Thus, reduction rate was proportional to mechanical work rate. If the stable grain size achieved during deformation depends on the product of stress and strain rate, rather than stress alone, then that grain size is an indication of the work rate and can be used as a paleowattmeter. Following this line of thought suggests that the gradient of recrystallized grain sizes that is often observed in the highly deformed portions of shear zones would not require a gradient in stress but could also be explained by material softening, resulting in locally elevated strain rates under constant stresses.

  3. Nonclassical crystallization: mesocrystals and morphology change of CaCO3 crystals in the presence of a polyelectrolyte additive.

    PubMed

    Wang, Tongxin; Cölfen, Helmut; Antonietti, Markus

    2005-03-16

    Crystallization of calcite from differently concentrated calcium chloride solutions by the CO2 gas diffusion technique in the presence of polystyrene sulfonate yields crystal superstructures with unusual morphology. From the typical calcite rhombohedra as a starting situation, the morphology can be systematically varied via rounded edges and truncated triangles to finally concavely bended lens-like superstructures. Although these "crystals" are apparently well-faceted in light microscopy, electron microscopy analysis and BET reveal that the structures are highly porous and are composed of almost perfectly 3D-aligned calcite nanocrystals scaffolded to the final, partly nicely curved superstructures. At high supersaturations, superstructures with changed symmetry indicative of dipolar interaction potentials between the building blocks are found. The present model case also gives evidence for the importance of nonclassical, mesoscopic processes in crystallization in general. PMID:15755119

  4. Addition of Calcite Reduces Iron’S Bioavailability in the Pennsylvania Coals—Potential Use Of Calcite for the Prevention Of Coal Workers’ Lung Diseases

    Microsoft Academic Search

    Qi Zhang; Xi Huang

    2005-01-01

    In the present study, a hypothesis was tested that the addition of calcite into the Pennsylvania coals may reduce levels of bioavailable iron (BAI), an important component in the mixed coal dust that may contribute to coal workers’ lung diseases. Predetermined proportions of calcite (0, 1, 2, 5, 10% w\\/w) were added into three PA coals. After suspending the mixtures

  5. 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.

  6. Statistical Evaluation of Cloud Seeding Operations

    Microsoft Academic Search

    K. A. Brownlee

    1960-01-01

    Modern commercial cloud seeding dates from the discovery in 1946 that silver iodide crystals are good nuclei for the formation of precipitation from cold clouds. Whether silver iodide seeding does actually increase the precipitation over what would occur naturally has been a controversial question.In 1953 Congress established the Advisory Committee on Weather Control, one of its responsibilities being to determine

  7. Water release patterns of heated speleothem calcite and hydrogen isotope composition of fluid inclusions

    Microsoft Academic Search

    Sophie Verheyden; Dominique Genty; Olivier Cattani; Martin R. van Breukelen

    2008-01-01

    Speleothem fluid inclusions are a potential paleo-precipitation proxy to reconstruct past rainwater isotopic composition (?18O, ?D). To get a better insight in the extraction of inclusion water from heated speleothem calcite, we monitored the water released from crushed and uncrushed speleothem calcite, heated to 900 °C at a rate of 300 °C\\/h, with a quadrupole mass spectrometer. Crushed calcite released water in

  8. 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.

  9. Calcite dissolution: an in situ study in the Panama Basin

    SciTech Connect

    Thunell, R.C. (Univ. of South Carolina, Columbia); Keir, R.S.; Honjo, S.

    1981-05-08

    The results of an in situ study of calcite dissolution in the Panama Basin indicate that the rate of dissolution in the water column increases suddenly below a water depth of about 2800 meters. This coincides with the depth at which the calcium carbonate content of surface sediments begins to decrease rapidly or the sedimentary lysocline. Since this level of increased dissolution both in the water column and on the sea floor does not appear to be related to the transition from supersaturation to undersaturation with respect to carbonate, there may be a kinetic origin for the lysocline in this region.

  10. Silicon Crystal Pulling

    NSDL National Science Digital Library

    This Quicktime animation shows the first step in the silicon wafer manufacturing process. Under 15 seconds in length, the animation shows the melting of polysilicon and the addition of minute amounts of electrically active elements to form the "seed" of the silicon crystal. The crystal is then extracted from the crystal-growing equipment.The next animation in this sequence about Silicon Ingot Rod Grinding can be seen here.

  11. 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.

  12. 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

  13. Nanocrystalline mirror-slip surfaces in calcite gouge sheared at sub-seismic slip rates

    NASA Astrophysics Data System (ADS)

    Verberne, B. A.; Plümper, O.; de Winter, D.; Niemeijer, A. R.; Spiers, C. J.

    2013-12-01

    If seismic-aseismic transitions in fault rocks are to be recognized from microstructures preserved in natural fault rocks, an understanding of the microphysical mechanisms that produce such microstructures is needed. We report on microstructures recovered from dry direct shear experiments on (simulated) dry calcite gouge, performed at 50 MPa normal stress, 18-150°C and low sliding velocities (0.1-10 ?m/s). The mechanical data show a transition from velocity strengthening below ~80°C to velocity weakening slip at higher temperatures. We investigated both loose gouge fragments and thin sections, characterizing the microstructures at the mm- to nm-scales. All deformed samples split along a shear band fabric defined by mainly R1- and boundary shears. Viewed normal to the shear plane, these bands commonly showed shiny, elongate patches aligned, and striated, parallel to the shear direction. These patches were especially common in samples tested below 80°C, though shear band splitting was less well-developed above 80°C so that even if the shiny patches formed at higher temperature they were less frequently exposed. Scanning Electron Microscopy (SEM) applied to shiny patches formed in samples sheared at room temperature showed the presence of elongate, streaked out sub-micron-sized particles oriented parallel to the shear direction. Transmitted light optical microscopy of thin sections cut normal to the shear plane and parallel to the shear direction, combined with Focused Ion Beam (FIB) - SEM on loose gouge fragments, showed that the shiny surfaces correspond with shear bands characterized by extreme grain size reduction and sintered sub-micron-particles. Transmission Electron Microscopy (TEM) further revealed that the cores of the shear bands consist of nanocrystallites some 20 nm in size, with a Crystallographic Preferred Orientation (CPO). Our results demonstrate that mirror-like nanocrystalline slip zones can form in calcite gouge sheared at shallow crustal conditions at sub-seismic sliding velocities, in velocity strengthening as well as velocity weakening samples. This means that their presence cannot be used as a single diagnostic indicator for seismic slip in natural fault rocks. Our SEM and TEM observations suggest that, at room temperature, the frictional behavior of the shear bands is dominated by crystal plastic plus nanogranular flow mechanisms, rather than by brittle deformation processes - as inferred for frictional slip in some metals. We further suggest that it is the thermally activated nature of crystal plasticity that is responsible for the transition from velocity strengthening to velocity weakening slip that we observed at ~80°C. The inferred mechanism has important implications for understanding both the depth range of seismicity and the seismic cycle in tectonically-active carbonate terrains.

  14. Using Clumped Isotopes To Help Understand Isotopic Sector Zoning In Calcite

    NASA Astrophysics Data System (ADS)

    Jourdan, A.; John, C. M.; Inchenko, A.; Davis, S.

    2010-12-01

    Debated among scientists for decades, observations of compositional differences between different crystallographic faces within a same growth zone -called sector zoning- represents a major challenge for geochemistry, and in particular for isotope geochemistry. Nowadays, convincing evidence for the existence of sector zoning has been reported in the literature. However, no consensus on the mechanisms triggering sector zoning has been reached. Understanding how and why sector zoning occurs is essential because the presence of sector zoning could skew the isotopic characterization of a carbonate mineral depending on the area being sampled. This would result in an ambiguous interpretation of the data. The emphasis of this study, which is part of the Qatar Carbonates and Carbon Research Center (QCCSRC), is thus placed on deciphering different processes leading to isotopic sector zoning in calcite, with the help of a new tool: the clumped isotopes (i.e. isotopologues). Large calcite crystals with clearly visible growth zones have been collected from fracture infills in Oman. The minerals growth zones and sectors are recognized via cathodoluminescence microscopy, and the trace element content of the different zones in several sectors is estimated via electron microprobe. These different sectors are then sampled by a micro-drill following single growth zones and analyzed for their oxygen and carbon isotopic compositions. The approach highlighted above allows for the recognition of the presence of sector zoning, but does not constrain the type of mechanism(s) possibly affecting isotopic fractionation. To gain further insight, we turn to clumped isotopes (multiply substituted isotopologues) which are molecules with distinct chemical and physical properties. This should theoretically lead to distinctive fractionations. Clumped isotopes have been used recently to measure the temperature of precipitation of carbonate minerals. If each of the crystalline phases of a given crystal were precipitated under thermodynamic equilibrium, one would expect a constant clumped isotope value between sectors. We intend to use clumped isotopes as a discriminative geochemical tool to check if any differences in the ?47 values between sectors exist. If this is the case, isotopologues could provide new insights on sector zoning and would give an extra-dimension to the quest of the different factors resulting in these type of isotopic zonations. Combining compositional, stable isotopes and clumped isotopes information could ultimately permit to reveal the secrets of sector zoning.

  15. 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.

  16. Compositional and kinetic studies on the crystallization of zeolite beta using cost-efficient TEABr without seed under static and stirred conditions

    NASA Astrophysics Data System (ADS)

    Lee, Young Jong; Kim, Shin Dong; Byun, Soon Churl; Park, Jun Woo; Jeong, Yeon Jun; Kwon, Yoon Jung; Song, Hee Oeul; Kim, Wha Jung

    2006-12-01

    Zeolite beta was successively synthesized in the presence of TEABr as organic template within 36 h under static and stirred conditions at 423 K. In order to clearly demonstrate the effects of individual component and interaction between components on the crystallization of zeolite beta using TEABr, a ternary compositional diagram for TEABr, Al 2O 3 and Na 2O was drawn at constant SiO 2 and H 2O contents. There are mainly three compositional zones in which zeolites, beta, ZSM-5 and mordenite are formed. The results suggest that Na + cation should have acted as structure-directing agent as well as charge balancing for AlO 2-, leading the crystallization toward the formation of mordenite or ZSM-5 depending on its content. The results clearly show that the crystallization toward pure zeolite beta becomes favorable at lower Al 2O 3 content. In addition, it is interesting to notice that Na 2O and Al 2O 3 contents would play key roles simultaneously in the crystallization toward the formation of pure zeolite beta. The results of thermal analysis show that TEA + ion also partially acts as charge-balancing agent depending on Al content, that is, it is more likely to interact with Si-O - rather than with Al-O - at lower Al content, thus resulting in the more decomposition of TEA + ions interacting with Si-O - at lower Al content in temperature range between 473 and 623 K. The kinetic study based on 3Na 2O-18TEABr-0.8Al 2O 3-25SiO 2-440H 2O was conducted at 413, 418 and 423 K, respectively, and the results suggest that as long as a correct crystallization temperature is applied to the synthesis of zeolite beta, the crystallization of zeolite beta does not seem to be so sensitive to temperature.

  17. 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.

  18. 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 [Institite 'Jozef Stefan', Jamova 39, SI-1000 Ljubljana (Slovenia)]. E-mail: zoran.samardzija@ijs.si; Jeon, Jae-Ho [Korea Institute of Machinery and Materials, 66 Sangnam-Dong, Changwon (Korea, Republic of); Ceh, Miran [Institite 'Jozef Stefan', Jamova 39, SI-1000 Ljubljana (Slovenia)

    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.

  19. Many Seeds: Estimating Hidden Seeds

    NSDL National Science Digital Library

    2012-06-26

    In this activity, learners will estimate how many seeds are in a fruit or vegetable, then count to find out. The result: mix estimation with healthy eating. Vary the level of difficulty by using different foods: for younger learners, choose something with up to about 15 seeds inside (e.g. apples, snow peas); for a medium level of difficulty, try melon slices or cucumbers; for more challenge, use pomegranates or mini-pumpkins. Available as a web page or downloadable pdf.

  20. Assessing the potential for using biogenic calcites as dosemeters for luminescence dating

    Microsoft Academic Search

    G. A. T. Duller; K. E. H. Penkman; A. G. Wintle

    2009-01-01

    Calcium carbonate emits an intense thermoluminescence (TL) signal and previous work has explored the potential of using this signal to date both inorganic carbonates such as limestones and stalagmites and biogenic calcite produced by marine organisms. Luminescence analysis of biogenic calcites directly dates the secretion of the mineral by the organism and is therefore not reliant upon exposure of the

  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 have stronger effects on acute step edges, a crossover occurs for the longer Asp4,5,6 peptides suggest a process by which small fluctuations in primary structure in proteins can control calcite shape

  2. Oil and Gas CDT Calcite-Aragonite Seas and porosity prediction: A New

    E-print Network

    Henderson, Gideon

    Oil and Gas CDT Calcite-Aragonite Seas and porosity prediction: A New Approach The University-risking of shallow-marine carbonate drilling targets. Methodology Research will begin by undertaking a new literature of biominerals to provide new insights into which Figure 1. Rough guide to proposed intervals of calcite

  3. Uranium in foraminiferal calcite as a recorder of seawater uranium concentrations

    Microsoft Academic Search

    A. D. Russell; S. Emerson; B. K. Nelson; J. Erez; D. W. Lea

    1994-01-01

    The authors present results of an investigation of uranium\\/calcium ratios in cleaned foraminiferal calcite as a recorder of seawater uranium concentrations. For accurate reconstruction of past seawater uranium content, shell calcite must incorporate uranium in proportion to seawater concentration and must preserve its original uranium composition over time. Laboratory culture experiments with live benthic (Amphistegina lobifera) and live planktonic (Globigerinell

  4. Research paper Uranium loss and aragoniteecalcite age discordance in a calcitized aragonite

    E-print Network

    Asmerom, Yemane

    Research paper Uranium loss and aragoniteecalcite age discordance in a calcitized aragonite Aragonite Recrystallization Uranium series dating Laser ablation MC-ICPMS a b s t r a c t We analyzed uranium-series concentrations and isotopic ratios in a mixed aragonite and calcite stalagmite from

  5. 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. (Statoil, Stavanger (Norway)); Walderhaug, O. (Rogaland Research, Stavanger (Norway))

    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.

  6. Partitioning of Sr2+ into Calcite Precipitates Induced by Bacterial Ureolysis in Artificial Groundwater.

    NASA Astrophysics Data System (ADS)

    Mitchell, A. C.; Ferris, F. G.; Mancini, A.; Litwin, Y.

    2003-12-01

    A suite of experiments were performed to investigate the partitioning of Sr2+ (to mimic the radionuclide 90Sr) between calcite and groundwater, in response to the hydrolysis of urea by B. pasteurii under simulated in-situ aquifer conditions. Three duplicate experiments were performed at 25° C over 8 days in microcosms inoculated with B. pasteurii ATCC 11859 and containing an artificial groundwater (AGW). The AGW composition was based upon the aqueous chemistry of the metal and radionuclide contaminated Snake River Plain Aquifer, Idaho,USA. Microcosms also contained 25 mM urea, and 1 mM of Sr as a contaminant treatment. Control experiments were run with non urea hydrolyzing bacteria, B. subtillus. Control experiments exhibited little change in pH, and dissolved ammonium and Ca2+ concentrations. Conversely during experiments inoculated with B. pasteurii, ammonium production increased asymptotically, peaking two days into the experiment when approximately all urea had been hydrolyzed. The production of ammonium and bicarbonate from urea hydrolysis caused an asymptotic increase in pH from 6.5 to 9.1 one day into the experiment. Dissolved Ca2+ and Sr2+ decreased asymptotically from the beginning of the experiment, and was accompanied by the development of solid precipitates identified as calcite by X-Ray diffraction. This caused an asymptotic decrease in the saturation state of calcite (S) after one day of the experiment. Specific rate constants were derived for calcite precipitation and critical saturation state from the time course data following a second-order chemical affinity based law. Calcite precipitation rate is fundamentally controlled by, and exhibits a positive association with S. Mass balance indicates the percentage of total Sr (dissolved and in calcite) incorporated into the calcite precipitate increases rapidly to 59 % after two days of the experiment, and increases less rapidly thereafter to a maximum of 67 %. Corresponding measured distribution coefficients (DMe) exhibit a positive association with S and calcite precipitation rates. Therefore DMe is greatest after one day of the experiment (DMe maximum = 0.39), which corresponds to the highest S and calcite precipitation rate, and decreases thereafter (DMe minimum = 0.16) as S and calcite precipitation rate decreases. Therefore the extent of Sr incorporation into calcite precipitates resulting from the hydrolysis of urea by B. pasteurii appears to be a primary function of precipitation rate, which is controlled by S. The median DMe determined by this study (0.22) is greater than previously published coefficients for Sr in calcite by up to an order of magnitude. This demonstrates the potential of calcite precipitation by bacterial ureolysis as a remediation strategy for 90Sr in calcite saturated aquifers.

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. Scleractinian corals produce calcite, and grow more slowly, in artificial Cretaceous seawater

    NASA Astrophysics Data System (ADS)

    Ries, Justin B.; Stanley, Steven M.; Hardie, Lawrence A.

    2006-07-01

    The mineralogies of most biotic and abiotic carbonates have alternated in synchroneity between the calcite (hexagonal) and aragonite (orthorhombic) polymorphs of CaCO3 throughout the Phanerozoic Eon. These intervals of calcite and aragonite production, or calcite seas and aragonite seas, are thought to be caused primarily by secular variation in the molar magnesium/calcium ratio of seawater (mMg/Ca > 2 = aragonite + high-Mg calcite; mMg/Ca < 2 = low-Mg calcite), a ratio that has oscillated between 1.0 and 5.2 throughout the Phanerozoic. In laboratory experiments, we show that three species of scleractinian corals, which produce aragonite in modern seawater and which have flourished as important reef builders primarily during aragonite seas of the past, began producing calcite in artificial seawater with an ambient mMg/Ca ratio below that of modern seawater (5.2). The corals produced progressively higher percentages of calcite and calcified at lower rates with further reduction of the ambient mMg/Ca ratio. In artificial seawater of imputed Late Cretaceous composition (mMg/Ca = 1.0), which favors the precipitation of the calcite polymorph, scleractinian corals produced skeletons containing >30% low-Mg calcite (skeletal mMg/Ca < 0.04). These results indicate that the skeletal mineral used by scleractinian corals is partially determined by seawater chemistry. Furthermore, slow calcification rates, resulting from the production of largely aragonitic skeletons in chemically unfavorable seawater (mMg/Ca < 2), probably contributed to the scleractinians' diminished reef-building role in the calcite seas of Late Cretaceous and early Cenozoic time.

  12. Critical occlusion via biofilm induced calcite precipitation in porous media

    NASA Astrophysics Data System (ADS)

    Zhang, Tianyu; Klapper, Isaac

    2014-05-01

    A model for biofilm induced calcite precipitation with pressure driven flow is presented at the scale of a single pore within a porous medium. The system, an extension of previous work (Zhang and Klapper 2010 Water Sci. Technol. 61 2957-64, Zhang and Klapper 2011 Int. J. Non-Linear Mech. 46 657-66), is based on a mixture model including biomaterial, mineral, and water with dissolved components. Computational results suggest the possibility of critical occlusion in the sense that there is a distinguished trans-pore pressure head such that for pressure drops below this level, pore clogging occurs relatively quickly while for pressure drops above, clogging occurs after much longer times if at all. Beyond its relevance to engineered biofilm applications, this phenomenon is suggestive of the subtleties of embedding simple biofilm models in larger media.

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

    SciTech Connect

    Radha, A. V. [Peter A. Rock Thermochemistry Lab. and Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit (NEAT ORU), Univ. of California, Davis, CA (United States); Forbes, Tori Z. [Peter A. Rock Thermochemistry Lab. and Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit (NEAT ORU), Univ. of California, Davis, CA (United States); Killian, Christopher E. [Univ. of Wisconsin, Madison, WI (United States); Gilbert, P.U.P.A [Univ. of Wisconsin, Madison, WI (United States); Navrotsky, Alexandra [Peter A. Rock Thermochemistry Lab. and Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit (NEAT ORU), Univ. of California, Davis, CA (United States)

    2010-09-21

    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.

  14. Stable calcium isotope composition of a pedogenic carbonate in forested ecosystem: the case of the needle fibre calcite (NFC).

    NASA Astrophysics Data System (ADS)

    Milliere, Laure; Verrecchia, Eric; Gussone, Nikolaus

    2014-05-01

    Calcium (Ca), carbon (C) and oxygen (O) are important elements in terrestrial environment, as their biogeochemical cycles are directly related to the storage of atmospheric carbon. Nevertheless, contrarily to C and O, Ca isotope composition has been only poorly studied in the terrestrial carbonates. Needle Fibre Calcite (NFC) is one of the most common pedogenic carbonates, unless its origin is still under debate. Recent studies explain its formation by precipitation inside fungal hyphae. Due to this possible biogenic origin, NFC can be considered as a potential bridge between the biochemistry (precipitation inside organic structure) and geochemistry (pedogenic carbonate related to soil conditions) of the Ca. Thus, the study of the Ca isotope composition of NFC seem to be of first interest in order to shed light on the behaviour of Ca in terrestrial environment, especially when precipitation of secondary carbonates is involved. The sampling site is situated in the Swiss Jura Mountains and has been chosen due to a previous complete study of the C and O isotope composition of NFC in relation to the ecosystem, which represent a good precondition for the understanding of the NFC Ca isotope signatures in this context. In this study, the implication of the fungi in the origin of NFC is investigated, by comparing the Ca isotope composition of NFC and a purely physicochemical calcite cement (LCC), both precipitated in the same environment. The ?44Ca signature of NFC and LCC crystals were used to determine possible differences of the precipitation rate during their formation. NFC and LCC have similar ?18O composition and are supposed to precipitate at the same temperature (Milliere et al., 2011a). Thus the study of Ca isotope composition of NFC seems to demonstrate that the elongated shape of the calcite needle can be explained by different precipitation processes than the rhombohedric calcite crystals precipitated in the same environment; and more precisely, the specific shape of NFC could be ascribed to a growth related to fungal organic molecules or potentially inside fungal hyphae. Three microscopic morphologies of NFC, previously defined (Milliere et al., 2011a), have been also examined in order to trace the evolution of the NFC inside the soil porosity. The Ca isotope composition of the simple needles, which are supposed to be the original form of NFC are the less fractionated compared to the soil solution, whereas the Ca isotope composition of the two other microscopic morphologies, namely the simple needle with nanofibres and the simple needle with overgrowths, are more fractionated, like the LCC, indicating potentially the influence of biogenic processes in the formation of the simple needles. Milliere L, Hasinger O, Bindschedler S, Cailleau G, Spangenberg JE, Verrecchia EP. 2011a. Stable carbon and oxygen isotopic signatures of pedogenic needle fibre calcite. Geoderma 161, 74-87.

  15. Phosphorus Removal Characteristics in Hydroxyapatite Crystallization Using Converter Slag

    Microsoft Academic Search

    EUNG-HO KIM; HWAN-KOOK HWANG; SOO-BIN YIM

    2006-01-01

    This study was performed to investigate the phosphorus removal characteristics in hydroxyapatite (HAP) crystallization using converter slag as a seed crystal and the usefulness of a slag column reactor system. The effects of alkalinity, and the isomorphic-substitutable presence of ionic magnesium, fluoride, and iron on HAP crystallization seeded with converter slag, were examined using a batch reactor system. The phosphorus

  16. International Seed Saving Institute: Basic Seed Saving

    NSDL National Science Digital Library

    This straightforward site from the International Seed Saving Institute on Basic Seed Saving will be of use to any growers interested in learning how to save seeds from season to season. The site provides links "to specific seed saving instructions for 27 common vegetables" including many favorites like corn, carrots, broccoli, and lettuce. The site also links to a glossary of seed saving terms and a six-step Seed Saving Tutorial.

  17. Seed Catalogues

    NSDL National Science Digital Library

    The Smithsonian Institutions Libraries Web site currently features a unique collection of seed and nursery catalogs dating from 1830 to the present. Online visitors may view a portion of the exhibit, which offers a look at "the history of the seed and agricultural implement business in the United States, as well as provides a history of botany and plant research such as the introduction of plant varieties into the US." Although this site does include much material, gardeners and anyone else with a horticultural bent should enjoy a casual browse through the online exhibit.

  18. Shock temperature in calcite (CaCO3) at 95^160 GPa Satish C. Gupta 1

    E-print Network

    Stewart, Sarah T.

    Shock temperature in calcite (CaCO3) at 95^160 GPa Satish C. Gupta 1 , Stanley G. Love 2 , Thomas J The temperatures induced in crystalline calcite (CaCO3) upon planar shock compression (95^160 GPa) are reported likely that shock-induced decomposition of calcite occurs behind the shock front. We modeled

  19. Big Seed

    NSDL National Science Digital Library

    2012-12-06

    This free iOS app helps develop spatial reasoning and strategic thinking. Users reflect seed squares (horizontally, vertically and diagonally) to grow larger pieces that eventually cover the given design space without spilling over. A graduated set of difficulty levels makes the game accessible to a wide range of ages.

  20. Seed Bargains

    NSDL National Science Digital Library

    Richard Konicek-Moran

    2008-04-01

    Children as well as adults are usually intrigued by the ideas of bargains. More seeds for less money is often enough to convince them to buy a larger, cheaper package. In this case, the children are savvy enough to question the value of either package. On

  1. 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

  2. Picosecond supercontinuum generation seeded by a weak continuous wave

    NASA Astrophysics Data System (ADS)

    Li, Ying; Hou, Jing; Leng, Jin-Yong; Wang, Wen-Liang; Jiang, Zong-Fu

    2013-07-01

    We experimentally investigate the spectral details of a picosecond supercontinuum pumped at 1064 nm and seeded by a weak continuous wave (~20000 times weaker than the pulse peak power) at several power levels in photonic crystal fibers. Seeding at different wavelengths leads to different spectral details and the effects to the bandwidth of supercontinuum are also distinct. Spectra can be widened when seeded by a continuous wave at 1070 nm and narrowed by ~ 100 nm when seeded at 1080 nm. The influence is enhanced by increasing the average seeded power.

  3. Crystal Growth and the Role of the Organic Network in Eggshell Biomineralization

    Microsoft Academic Search

    Heather Silyn-Roberts; R. M. Sharp

    1986-01-01

    A model based on geometrical crystal growth considerations is proposed for the deposition of the crocodilian, testudinian and avian eggshells. In each shell column, crystal deposition is initiated at a single location, from which growth fans out at all angles to the shell normal. In both calcitic and aragonitic shells, growth is in the [001] direction, resulting in an increase

  4. 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 ...

  5. The Role of Deformation on the Microstructural Evolution of Calcite

    NASA Astrophysics Data System (ADS)

    Austin, N. J.; Evans, B.

    2005-12-01

    Ductile shear zones are frequently spatially associated with a reduced grain-size, in a progression from undeformed protomylonites to fine grained ultramylonites. The kinetics of the microstructural evolution towards this modified grain-size, and its relationship to the mechanical properties, however, remains unclear. This work presents a series of hydrostatic and constant force, conventional triaxial deformation experiments performed on reagent grade calcite, between 823 and 1023 K, at a confining pressure of 300 MPa, and differential stresses between 0 and 40 MPa. In deformation experiments, stresses were applied such that deformation should be accommodated purely by diffusion creep, or by a combination of diffusion and dislocation creep (± grain boundary sliding), based on pre-existing flow laws. Under static conditions, grain-growth kinetics agree with those observed by Freund et al. (2001) for >99.9% pure calcite, containing trace amounts of Mn. Under conditions of low differential stress, or for fine-grained samples, grain-growth is indistinguishable from that under static conditions. For high stresses, or for coarse-grained samples, grain-size reduction is observed, the kinetics of which are correlated with the strain-rate and grain-size. The onset of grain-size reduction correlates with an increased component of dislocation creep. All samples that exhibit grain-size reduction have other features indicative of dislocation creep, including irregular grain boundaries, and progressive flattening of grains, whereas all samples that exhibit grain-growth during deformation have polygonal grains that are indistinguishable from those produced under static conditions. Further, at the conditions of our experiments, samples that exhibit grain-size reduction plot in the transitional deformation regime of Walker et al. (1990), whereas all of those that exhibit grain-growth plot in the diffusion creep field. The observed grain size reduction kinetics are best explained by summing the calculated reduction rate (drate=?rated?c-1), with the predicted parabolic growth rate from Freund et al. (2001), as formulated by Hall and Parmentier (2003). The transition between grain-growth and grain-size reduction observed in our experiments can be explained by equating growth and reduction kinetics. When these kinetics are extrapolated to temperatures (523-623K) and strain rates (10-10 to 10-11 s-1) consistent with natural shear zones, the predicted grain size is similar to that measured in shear zones in the Swiss Helvetic Alps (Herwegh et al., 2005). These data suggest that it may be possible to obtain a robust relationship between grain-size and strain-rate that, when coupled with knowledge of metamorphic conditions, may allow natural strain rates to be estimated.

  6. Seeding of high temperature air flow

    NASA Astrophysics Data System (ADS)

    Rusch, D.; Kempe, A.; Roesgen, T.

    2007-05-01

    Seeding of high temperature air flows is problematic because common seeding materials can ignite and may pose a threat for human health in case of inhalation. Sodium chloride is proposed as a seeding material to avoid these problems. The generation of crystals using an ultrasonic atomizer is described and the measured particle size distribution is presented. The described method has the additional advantage that the particle size can easily be adjusted. This allows the operator to comply with the experimental requirements in terms of resolvable frequencies. The described method has been successfully applied to LDA measurements in a 500°C air flow.

  7. Stress remagnetization in pyrrhotite-calcite synthetic aggregates

    NASA Astrophysics Data System (ADS)

    Robion, Philippe; Borradaile, Graham J.

    2001-01-01

    Stress-induced remagnetization has been applied to multidomain pyrrhotite-calcite synthetic aggregates in a triaxial rig. Experimental deformation used 150MPa confining pressure, a constant strain rate of 10-5 s-1 and applied differential stresses of up to 70MPa. New components of magnetization, parallel to the direction of the pressure vessel field, were added to the pre-deformational magnetization. The intensity of remagnetization (M'-M0) increases with the intensity of the applied differential stress and affects the coercivity fraction below 15mT. Bulk shortening is less than 8 per cent, thus grain rotation cannot explain selective remagnetization of the low-coercivity fraction. Remagnetization is thus attributed to deformational viscous remanent magnetization (DVRM). It is observed that high-coercivity (>15mT) grains do not remagnetize. There is, however, slight progressive rotation of pre-deformational magnetization with increasing strain up to 8 per cent of bulk shortening. The lack of piezoremanent magnetization in the high-coercivity range may be due to defects introduced in pyrrhotite during sample preparation. Experiments using synthetic pyrrhotite, expected to show low dislocation densities, would be necessary to test this effect.

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

    E-print Network

    Cirpka, Olaf Arie

    in the subsurface or fracking could be reduced with sealing technologies like microbially induced calcite Injectionwellvicinity Fracking CO2 Reservoir Figure 1: Potential application sites of MICP as a sealing technology

  9. 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)

  10. 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

    2015-02-01

    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.

  11. 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.

  12. 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.

  13. 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.

  14. Synthetic polycrystalline aragonite to calcite transformation kinetics: experiments at pressures close to the equilibrium boundary

    Microsoft Academic Search

    W.-L. Huang

    2003-01-01

    Summary ¶This study experimentally investigated the transformation kinetics of synthetic polycrystalline aragonite to calcite at four temperature\\/pressure conditions (330?°C\\/200?MPa, 380?°C\\/325?MPa, 430?°C\\/580?MPa, and 480?°C\\/875?MPa), close to the calcite-aragonite equilibrium phase boundary. The extents of transformation measured as a function of time in a synthetic system, using in-situ annealed, high purity samples, are consistent with the kinetic model for grain-boundary nucleation and

  15. Fractionation of carbon and oxygen isotopes and magnesium between coexisting metamorphic calcite and dolomite

    Microsoft Academic Search

    Simon M. F. Sheppard; Henry P. Schwarcz

    1970-01-01

    Fractionations of carbon and oxygen isotopes and magnesium between coexisting dolomite and calcite have been determined for\\u000a marbles and calcareous schists of a wide variety of metamorphic environments from Vermont and the Grenville Province of Ontario.\\u000a Concordant equilibrium fractionations are given by 83% of the samples. Calibration of the isotopic thermometers using the\\u000a Mg-calcite solvus thermometer gave in the temperature

  16. Preferred orientation of calcite in deep-sea carbonates and its relationship to acoustic anisotropy 

    E-print Network

    Schaftenaar, Carl Howard

    1982-01-01

    PREFERRED ORIENTATION OF CALCITE IN DEEP-SEA CARBONATES AND ITS RELATIONSHIP TO ACOUSTIC ANISOTROPY A Thesis by CARL HOWARD SCHAFTENAAR Submitted to the Graduate college of Texas A&M University in partial fulf llment of the requirement... for the degree of MASTER OF SCIENCE August 1982 Major Subject: Geophysics PREFERRED ORIENTATION OF CALCITE IN DEEP-SEA CARBONATES AND ITS RELATIONSHIP TO ACOUSTIC ANISOTROPY A Thesis by CARL HONARD SCHAFTENAAR Approved as to style and content by: c...

  17. Laboratory determination of oxygen isotope fractionation of high Mg-calcite between 25 and 80°C

    Microsoft Academic Search

    V. Mavromatis; M. Schmidt; R. Botz

    2009-01-01

    High magnesium calcite (HMC) was synthesized from oversaturated solutions with respect to calcite at 25, 40, 60 and 80 ° C. A fractionated dissolution technique was applied, in order to remove any amorphous calcium carbonate (ACC) from synthesized Ca,Mg-carbonate. The occurrence of pure HMC (6-30% MgCO3) allowed the effect of Mg2+ on the oxygen isotope fractionation to be estimated. The

  18. 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)

  19. Seed Treatment. Manual 92.

    ERIC Educational Resources Information Center

    Missouri Univ., Columbia. Agricultural Experiment Station.

    This training manual provides information needed to meet minimum EPA standards for certification as a commercial applicator of pesticides in the seed treatment category. The text discusses pests commonly associated with seeds; seed treatment pesticides; labels; chemicals and seed treatment equipment; requirements of federal and state seed laws;…

  20. NMR characterization of hydrocarbon adsorption on calcite surfaces: A first principles study

    NASA Astrophysics Data System (ADS)

    Bevilaqua, Rochele C. A.; Rigo, Vagner A.; Veríssimo-Alves, Marcos; Miranda, Caetano R.

    2014-11-01

    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 Ca2+. 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 ( {10bar 14} )). 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 43Ca, 13C, and 17O 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.

  1. Estimation of past seepage volumes from calcite distribution in the Topopah Spring Tuff, Yucca Mountain, Nevada.

    PubMed

    Marshall, Brian D; Neymark, Leonid A; Peterman, Zell 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. PMID:12714293

  2. Cd sup 2+ uptake by calcite, solid-state diffusion, and the formation of solid-solution: Interface processes observed with near-surface sensitive techniques (XPS, LEED, and AES)

    SciTech Connect

    Stipp, S.L.; Hochella, M.F. Jr.; Parks, G.A.; Leckie, J.O. (Stanford Univ., CA (United States))

    1992-05-01

    X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES) allowed direct observations of structure and bonding environments at the calcite surface. Pure calcite crystals were cleaved from precleaned Iceland spar and were briefly exposed to aqueous solutions containing various concentrations of Cd{sup 2+}, CO{sub 3}{sup 2{minus}}, ClO{sub 4}{sup {minus}}, and/or Cl{sup {minus}}. LEED results demonstrate that the calcite surface is atomically ordered, even after hydration and cadmium uptake. {gamma}-scintillation data from crystals exposed briefly to solutions of {sup 109}Cd{sup 2+} indicate that surface uptake ranged from the equivalent of about 1 to 4 monolayers. XPS analyses in the first 2 hours after exposure detected Cd within the top 30 {angstrom}, but crystals stored in air or in ultra-high vacuum showed a decrease in Cd surface concentration with time such that after two days, C was barely detectable in the near-surface region. No Cd enrichment was observed at sites of surface defects using AES, indicating that solid-state diffusion into the mineral surface was not accomplished simply by migration along microfractures alone. This work suggests that solid-state diffusion may play a role in the rate and extent of uptake of certain trace metals from solution and probably leads to the formation of solid-solution in calcite and other carbonate minerals. It also suggests that the process of diffusion into the solid mineral host should be considered in hydrogeochemical models that intend to simulate and predict trace-metal mobility in carbonate terrains.

  3. Ideas for Discussing the Crystallization Demonstration in Class

    NSDL National Science Digital Library

    What is Happening in the Demonstration? The solid salicylate is melted and the resulting liquid then cooled, so that it freezes into a solid. Seeds (small crystals) of salicylate enhance the crystallization ...

  4. Self-seeding schemes for the European XFEL

    Microsoft Academic Search

    Gianluca Geloni; Vitali Kocharyan; Evgeni Saldin

    2011-01-01

    Due to start-up from shot noise, typical SASE XFEL pulses exhibit poor longitudinal coherence. Self-seeding schemes can be use to improve it. Recently, a novel single-bunch self-seeding scheme was proposed, based on a particular kind of monochromator, which relies on the use of a single crystal in Bragg-transmission geometry. In its simplest configuration, the self-seeded XFEL consists of an input

  5. 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.

  6. (100) Crystal Plane of Silicon

    NSDL National Science Digital Library

    This animation, created by Southwest Center for Microsystems Education (SCME), "illustrates the crystal growth of silicon using a seed crystal (or unit cell) positioned to the (100) plane. The silicon crystal grows into a large ingot which is sliced into silicon wafers. To verify the (100) plane of the wafer, the wafer is broken or cleaved causing it to break at 90 degree angles." The supporting Crystallography Learning Module and activities can be downloaded from the SCME website under Educational Materials.

  7. Seed Magazine

    NSDL National Science Digital Library

    Seed is an online (and print) magazine dedicated to increasing the scientific awareness and knowledge of the general public. The site is updated six days a week and features news articles, original-content articles on a variety of science topics, columns, and reviews. "Cribsheets," a downloadable feature, provide brief tutorials on scientific issues and innovations that may occur in everyday conversation. The magazine also features a collection of multimedia materials, such as podcasts, slide shows, and video content. The web site's main page features articles from the latest issue; back issues may be browsed by category, author, or date. Information about subscribing to the print version is also provided.

  8. Kinetics and mechanism of formation of gehlenite, Al-Si spinel and anorthite from the mixture of kaolinite and calcite

    NASA Astrophysics Data System (ADS)

    Ptá?ek, Petr; Opravil, Tomáš; Šoukal, František; Havlica, Jaromír; Holešinský, Radek

    2013-12-01

    The kinetics and mechanism of formation of gehlenite, Al-Si spinel phase, wollastonite and anorthite from the mixture of kaolinite and calcite was investigated by differential thermal analysis under the heating rate from 283 to 293 K min-1 using Kissinger equation. The changes in the phase composition of the sample during the thermal treatment were investigated via simultaneous TG-DTA, in situ high-temperature x-ray diffraction analysis and high-temperature heating-microscopy. The crystallizations of gehlenite and Al-Si spinel phase show apparent activation energy of (411 ± 5) kJ mol-1 and (550 ± 9) kJ mol-1, respectively. The value of kinetic exponent corresponds to the process limited by the decreasing nucleation rate for gehlenite while constant nucleation rate is determined for Al-Si spinel phase. Anorthite crystallizes from the eutectic melt and the process shows the apparent activation energy of (1140 ± 25) kJ mol-1. The process is limited by the constant nucleation rate of a new phase.

  9. 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.

  10. The role of disseminated calcite in the chemical weathering of granitoid rocks

    NASA Astrophysics Data System (ADS)

    White, Art F.; Bullen, Thomas D.; Vivit, Davison V.; Schulz, Marjorie S.; Clow, David W.

    1999-07-01

    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. CO 2, 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.

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

    E-print Network

    Benning, Liane G.

    , University of Leeds, Leeds, LS2 9JT, UK 2 Department of Earth Sciences, Oxford University, Parks Road, Oxford). * E-mail: v.payne@see.leeds.ac.uk DOI: 10.1180/minmag.2008.072.1.269 Mineralogical Magazine, February

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

    Microsoft Academic Search

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

    2003-01-01

    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

  13. Alfalfa Seed Testing. 

    E-print Network

    Ball, O. M. (Oscar Melville)

    1905-01-01

    of the various form may be gotten from Plate I. Note "^ AND WEED SEEDS FOUND IN ALFALFA SEED OF ALFALFA SEED OF HEALTHY COLOR. M EDICAGO SATIVA. OTHER CLOVER SEEDS SOMETIMES USED AS ADULTERANTS. I I .ILOT. WHITE. SWEET MELILOT. YELLOW. BURR CLOVER.... - MELILOTUS ALBA. MELILOTUS INDICA MEDICAGO DENTICULATA. S. PLANTAIN. TUMBLE WEED. LANCEOLATA. AMARANTHUS GRACILARIS. CARELESS WEED. AMARANTHUS HYBRIDUS. SPECIALLY NOXIOUS WEED SEEDS FREQUENTLY FOUND IN k ,' ALFALFA SEED. RUSSIAN THISTLE. , :? I...

  14. THE STRUCTURAL EVOLUTION OF LELY SEEDS DURING THE INITIAL STAGES OF SiC SUBLIMATION GROWTH

    E-print Network

    Rohrer, Gregory S.

    THE STRUCTURAL EVOLUTION OF LELY SEEDS DURING THE INITIAL STAGES OF SiC SUBLIMATION GROWTH V. D Science and Engineering Pittsburgh PA 15213, USA ABSTRACT The as-grown surfaces of 6H SiC seed crystals. The surfaces were then used to seed the sublimation growth of SiC at 2300'C, in 650 torr of Ar, with a gradient

  15. Improved germination of pansy seed at high temperatures by priming with salt solutions

    E-print Network

    Yoon, Beyoung-Han

    1995-01-01

    and nonprimed seeds. Pansy seeds (Viola x wittrockiana 'Majestic Giant Blue Shade' and 'Crystal Bowl Sky Blue') were primed with several salts and PEG 15,000 at - 1.0 and - 2.0 MPa, for 3, 6, or 9 days at 23 C. Total percent germination (G) of nonprimed seeds...

  16. 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.

  17. 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).

  18. Acceleration of calcite kinetics by abalone nacre proteins

    Microsoft Academic Search

    Germaine Fu; S. Roger Qiu; Christine A. Orme; Daniel E. Morse; James J. De Yoreo

    2005-01-01

    The fascinating shapes and hierarchical designs of biomineralized structures have long been an inspiration to materials scientists because of the potential they suggest for biomolecular control over synthesis of crystalline materials. One prevailing view is that mineral-associated macromolecules are responsible for initiating and stabilizing non-equilibrium crystal polymorphs and morphologies through interactions between anionic moieties and cations in solution or at

  19. Modulation of calcium oxalate monohydrate crystallization kinetics in vitro

    Microsoft Academic Search

    Dik J Kok; Socrates E Papafoulos; Leo J M J Blomen; Olav L M Bijvoet; S E Papapoulos

    1988-01-01

    Modulation of calcium oxalate monohydrate crystallization kinetics in vitro. The effects of several low and high molecular weight (mol wt) compounds on the kinetics of calcium oxalate crystallization were examined using a seeded crystal growth method in which the solubility, the growth and the agglomeration of calcium oxalate crystals were measured as three separate and system-independent parameters. Git-rate, magnesium, phosphate,

  20. 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.

  1. Microbial dissolution of calcite at T = 28 °C and ambient pCO 2

    NASA Astrophysics Data System (ADS)

    Jacobson, Andrew D.; Wu, Lingling

    2009-04-01

    This study used batch reactors to quantify the mechanisms and rates of calcite dissolution in the presence and absence of a single heterotrophic bacterial species ( Burkholderia fungorum). Experiments were conducted at T = 28°C and ambient pCO 2 over time periods spanning either 21 or 35 days. Bacteria were supplied with minimal growth media containing either glucose or lactate as a C source, NH 4+ as an N source, and H 2PO 4- as a P source. Combining stoichiometric equations for microbial growth with an equilibrium mass-balance model of the H 2O-CO 2-CaCO 3 system demonstrates that B. fungorum affected calcite dissolution by modifying pH and alkalinity during utilization of ionic N and C species. Uptake of NH 4+ decreased pH and alkalinity, whereas utilization of lactate, a negatively charged organic anion, increased pH and alkalinity. Calcite in biotic glucose-bearing reactors dissolved by simultaneous reaction with H 2CO 3 generated by dissolution of atmospheric CO 2 (H 2CO 3 + CaCO 3 ? Ca 2+ + 2HCO 3-) and H + released during NH 4+ uptake (H + + CaCO 3 ? Ca 2+ + HCO 3-). Reaction with H 2CO 3 and H + supplied ˜45% and 55% of the total Ca 2+ and ˜60% and 40% of the total HCO 3-, respectively. The net rate of microbial calcite dissolution in the presence of glucose and NH 4+ was ˜2-fold higher than that observed for abiotic control experiments where calcite dissolved only by reaction with H 2CO 3. In lactate bearing reactors, most H + generated by NH 4+ uptake reacted with HCO 3- produced by lactate oxidation to yield CO 2 and H 2O. Hence, calcite in biotic lactate-bearing reactors dissolved by reaction with H 2CO 3 at a net rate equivalent to that calculated for abiotic control experiments. This study suggests that conventional carbonate equilibria models can satisfactorily predict the bulk fluid chemistry resulting from microbe-calcite interactions, provided that the ionic forms and extent of utilization of N and C sources can be constrained. Because the solubility and dissolution rate of calcite inversely correlate with pH, heterotrophic microbial growth in the presence of nonionic organic matter and NH 4+ appears to have the greatest potential for enhancing calcite weathering relative to abiotic conditions.

  2. A method to produce microseed stock for use in the crystallization of biological macromolecules.

    PubMed

    Luft, J R; DeTitta, G T

    1999-05-01

    A method is presented for producing a seed-stock mixture for macromolecular crystallization. A PTFE bead and micro-centrifuge tube act as mortar and pestle for pulverizing seed crystals of macromolecules. Energy for the bead's motion is supplied by a vortex mixer or an ultrasonic bath. The crushed crystal is serially diluted to prepare a seed-stock mixture of the desired concentration for crystallization. Crystals produced using both hanging-drop vapor diffusion and a capillary microbatch method show expected dilution behavior. This technique of producing seed stock is compared with traditional means and advantages over the standard protocol are demonstrated. PMID:10216295

  3. Ca-Mg inter-diffusion in synthetic polycrystalline dolomite-calcite aggregate at elevated temperatures and pressure

    Microsoft Academic Search

    Wuu-Liang Huang; Teh-Ching Liu; Pouyan Shen; Allen Hsu

    2009-01-01

    This study measures the reaction rate of dolomite and aragonite (calcite) into Mg-calcite at 800, 850, and 900°C and 1.6 GPa.\\u000a The dry synthetic dolomite-aragonite aggregate transformed very rapidly into dolomite-calcite polycrystalline aggregate while\\u000a Mg-calcites formed at a relatively slow rate, becoming progressively richer in Mg with run time. We modeled the reaction progress\\u000a semi-empirically by the first-order rate law. The

  4. Control of crystal phase switching and orientation by soluble mollusc-shell proteins

    Microsoft Academic Search

    A. M. Belcher; X. H. Wu; R. J. Christensen; P. K. Hansma; G. D. Stucky; D. E. Morse

    1996-01-01

    IN the initial stages of the biomineralization of abalone shells, a primer layer of oriented calcite crystals grows on a nucleating protein sheet1,2. The deposition of this primer is followed by an abrupt transition to c-axis-oriented crystals of aragonite, another crystalline form of calcium carbonate. The formation of each of the two crystal types is accompanied by the synthesis of

  5. Watermelon Seed Germination

    E-print Network

    Watermelon Seed Germination Purdue University Cooperative Extension Service BP-62 Seed Germination seeds of standard watermelon. The concept of seedless fruit seem to fit the lifestyle of consumers who bars and fruit salads. Seedless watermelon are pro- duced from seed which have three sets

  6. How Seeds Travel

    NSDL National Science Digital Library

    Mrs Liston

    2009-11-09

    Students will rotate around to 7 different stations to identify how the 7 presented seeds travel, whether it be by wind, water, or animal. They will then record it in their plant journals by illustrating the seed, listing its characteristics, and identifying the way in which it travels. Designer Seeds 7 Stations Coconut-Water Maple Seed- Wind Burdock (burrs) - Animals ...

  7. Method and apparatus for growing crystals

    NASA Astrophysics Data System (ADS)

    Naumann, Robert J.; Lehoczky, Sandor L.; Frazier, Donald O.

    1988-04-01

    A method and apparatus for bulk growth of defect-free compound crystals is described. Crystal growth is conducted in this invention in an apparatus having an enclosure with a spherical interior provided with an adjustable heat source. A seed crystal is positioned within this interior and is connected to one end of a rod of heat conductive material which extends through the enclosure. The rod is independently heated, and a heat absorber is connected to an opposite end of the rod. Crystalline material is placed in the interior of the sphere and in engagement with the seed crystal and pressure is applied to it. Encapsulant material having a slightly lower melting point than the crystalline material is disposed between the latter and the spherical container wall. A crystal structure is grown by heating the crystalline material up to a set temperature while controlling heat dissipation through the rod by the application of heat to the rod. Heat application is reduced, allowing heat to escape via the seed crystal and the rod of the material, causing the crystalline material to be deposited as a single crystal on the seed crystal. The novelty of the invention is believed to reside in the use of a spherical container with with a heat removal rod at one pole of the sphere, the rod providing control of the shape of the crystal-liquid interface during solidification. These feature permit growth of relatively large, defect-free crystals of compound materials.

  8. Calcium carbonate crystallization in the presence of modified polysaccharides and linear polymeric additives

    NASA Astrophysics Data System (ADS)

    Matahwa, H.; Ramiah, V.; Sanderson, R. D.

    2008-10-01

    Crystallization of calcium carbonate was performed in the presence of grafted polysaccharides, polyacrylamide (PAM) and polyacrylic acid (PAA). The grafted polysaccharides gave crystal morphologies that were different from the unmodified polysaccharides but similar to the ones given by homopolymers of the grafted chains. PAM-grafted ?-cellulose gave rectangular platelets that aggregated to form 'spherical' crystals on the surface of the fiber, whereas PAA grafted ?-cellulose gave spherical crystals on the surface of the fiber. X-ray diffraction (XRD) spectroscopy showed that PAM-grafted ?-cellulose, PAM as well as the control (no polymeric additive) gave calcite crystals at both 25 and 80 °C. However, the PAA-grafted ?-cellulose and PAA homopolymer gave calcite and vaterite crystals at 25 °C with calcite and aragonite crystals along with traces of vaterite being formed at 80 °C. The fiber surface coverage by these crystals was more on the acrylic- and acrylamide-grafted cellulose than on the ungrafted ?-cellulose. The evolution of CaCO 3 polymorphs as well as crystal morphology in PAA-grafted starch was similar to that of PAA-grafted ?-cellulose at the two temperatures employed.

  9. Arsenic incorporation in natural calcite lattice: Evidence from electron spin echo spectroscopy

    NASA Astrophysics Data System (ADS)

    Di Benedetto, Francesco; Costagliola, Pilario; Benvenuti, Marco; Lattanzi, Pierfranco; Romanelli, Maurizio; Tanelli, Giuseppe

    2006-06-01

    Quaternary travertines of the Middle Pecora Valley (Tuscany, Italy) contain up to 257 ppm arsenic. Such a content is environmentally relevant, but low enough to make the exact chemical speciation of arsenic difficult by applying conventional investigation techniques. The task was addressed by use of the Electron Spin Echo (ESE) spectroscopy, taking advantage from the modulation by the arsenic nucleus of the decay spectrum of the paramagnetic ion Mn(II), occurring as replacement of Ca in the calcite lattice. Interpretation of the spectra suggests that arsenic occurs in the calcite lattice in the position of C, through the substitution CO 2-3 ? AsO 3-3. This mechanism of arsenic incorporation by calcite may be an effective limit of arsenic mobility under conditions where immobilization through sorption by iron and/or manganese oxyhydroxides is not operating.

  10. 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.

  11. Vegetable Seed Saving Handbook

    NSDL National Science Digital Library

    This Vegetable Seed Saving Handbook online is a great resource for anyone wanting to harvest viable Fast Plants seeds to plant right away (as in selection experiments) or save for future use. Follow the instructions for cabbage family seeds (Brassica raps, in particular). If you're planning on saving your seeds, treat Fast Plants seeds as "desiccation-tolerant" as described here: http://howtosaveseeds.com/store.php

  12. 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.

  13. Fatty acids in sparry calcite fracture fills and microsparite cement of septarian diagenetic concretions

    NASA Astrophysics Data System (ADS)

    Pearson, M. J.; Hendry, J. P.; Taylor, C. W.; Russell, M. A.

    2005-04-01

    Sparry calcite fracture fills and concretion body cements in concretions from the Flodigarry Shale Member of the Staffin Shale Formation, Isle of Skye, Scotland, entrap and preserve mineral and organic materials of sedimentary and diagenetic origin. Fatty acids are a major component of the lipids recovered by decarbonation and comprise mainly n-alkanoic and ?-? dicarboxylic acids. Two generations of fracture-fill calcite (early brown and later yellow) and the concretion body microspar yield significantly different fatty acid profiles. Early brown calcites yield mainly medium-chain n-alkanoic acids with strong even predominance; later yellow calcites are dominated by ?-? dicarboxylic acids with no even predominance. Both fracture fills lack the long-chain n-alkanoic and ?-? dicarboxylic acids additionally recovered from the concretion bodies. The absence of longer chain acids in the calcite spar fracture fills is inferred to result from the transport of fatty acids by septarian mineralising fluids whereby low-aqueous solubility of longer chain acids or their salts accounts for their relative immobility. Comparative experiments have been carried out using conventional solvent extraction on the concretion body and associated shales, both decarbonated and untreated. Extracted lipid yields are higher, but the fatty acids probably derive from mixed locations in the rock including both kerogen- and carbonate-associated lipid pools. Only experiments involving decarbonation yielded ?-? dicarboxylic acids in molecular distributions probably controlled mainly by fluid transport. Alkane biomarker ratios indicate very low thermal maturity has been experienced by the concretions and their host sediments. Septarian cracks lined by brown calcite formed during early burial. Microbial CO 2 from sulphate-reducing bacteria was probably the main source of mineralising carbonate. Emplacement of the later septarian fills probably involved at least one episode of fluid invasion.

  14. 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

  15. Bioremediation of Pb-contaminated soil based on microbially induced calcite precipitation.

    PubMed

    Achal, Varenyam; Pan, Xiangliang; Zhang, Daoyong; Fu, Qinglong

    2012-02-01

    To remediate lead (Pb)-contaminated soils, it is proposed that microbially induced calcite precipitation (MICP) would provide the best alternative to other remediation technologies. In this study, Pb bioremediation in soils was investigated using the calcite-precipitating bacterium Kocuria flava. Results indicate that the Pb is primarily associated with the carbonate fraction in bioremediated soil samples. The bioavailability of Pb in contaminated soil was reduced so that the potential stress of Pb was alleviated. This research provides insight into the geochemistry occurring in the MICP-based Pb-remediated soils, which will help in remediation decisions. PMID:22370357

  16. Toward a conceptual model of the calcite surface: hydration, hydrolysis, and surface potential

    NASA Astrophysics Data System (ADS)

    Stipp, S. L. S.

    1999-10-01

    Because of a recent increase in interest in the properties of the calcite surface, there has also been an increase in activity toward development of mathematical models to describe calcite’s surface behaviour, particularly with respect to adsorption and precipitation. For a mathematical model to be realistic, it must be based on a sound conceptual model of atomic structure at the interface. New observations from high resolution techniques have been combined with previously published data to resolve the apparent conflict with results from electrokinetic studies and to present a picture of what the calcite surface probably looks like at the atomic scale. In ultra-high vacuum (10-10 mbar), a cleaved surface remains unreacted for at least an hour, but the unreacted surface does not remain as a termination of the bulk structure. X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and atomic force microscopy (AFM) show that the outer-most atomic layer relaxes and the surface slightly restructures. In air, dangling bonds are satisfied by hydrolysed water. XPS and time-of-flight secondary ion mass spectrometry (TOF-SIMS) reveal the presence of adsorbed OH and H. In AFM images, the features so typical of calcite, namely, alternate-row offset, pairing and height difference, as well as the consistent dependence of these features on the force and direction of tip scanning, are best explained by OH filling of the vacant O sites created during cleavage on the Ca octahedra. Thus there is solid evidence to indicate the presence of OH and H chemi-sorbed at the termination of the bulk calcite structure. Wet chemical studies, however, show that calcite’s pHpzc (zero point of charge) varies with sample history and solution composition. Electrophoretic mobility measurements indicate that the potential-determining ions are not H+ and OH-, but rather Ca2+ and CO32- (or HCO3- or H2CO30). This apparent conflict is resolved by a slight modification of the electrical double layer (EDL) model. At the bulk termination, hydrolysis species are chemi-bonded. At the Stern layer, adsorption attaches Ca2+ and CO32- (or other carbonate species), but the hydrolysis layer keeps them in outer-sphere coordination to the surface. With dehydration, loss of the hydrolysis species results in direct contact between adsorbed ions and the bulk termination, therefore, inner-sphere sorption is equivalent to extension of the three dimensional bulk network, which is precipitation. Attachment of ions with size and charge compatible with Ca and CO3 likewise results in coprecipitation and solid-solution formation.

  17. Effect of silk sericin on morphology and structure of calcium carbonate crystal

    NASA Astrophysics Data System (ADS)

    Zhao, Rui-Bo; Han, Hua-Feng; Ding, Shao; Li, Ze-Hao; Kong, Xiang-Dong

    2013-06-01

    In this paper, silk sericin was employed to regulate the mineralization of calcium carbonate (CaCO3). CaCO3 composite particles were prepared by the precipitation reaction of sodium carbonate with calcium chloride solution in the presence of silk sericin. The as-prepared samples were collected at different reaction time to study the crystallization process of CaCO3 by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and X-ray diffraction (XRD). The results showed that silk sericin significantly affected the morphology and crystallographic polymorph of CaCO3. With increasing the reaction time, the crystal phase of CaCO3 transferred from calcite dominated to vaterite dominated mixtures, while the morphology of CaCO3 changed from disk-like calcite crystal to spherical vaterite crystal. These studies showed the potential of silk sericin used as a template molecule to control the growth of inorganic crystal.

  18. Investigating the Basis of Biogenic Calcium Carbonate Formation from an Amorphous Precursor: Nature of the Transformation to Calcite on Hydroxyl Functionalized Surfaces

    NASA Astrophysics Data System (ADS)

    Wang, D.; Lee, J. R.; Talley, C. E.; Murphy, K. E.; Han, T. Y.; Deyoreo, J. J.; Dove, P. M.

    2006-12-01

    Calcium carbonate biominerals are particularly significant because of their direct role in regulating the global carbon cycle, as well as their ubiquitous occurrence across earth environments. Biogenic carbonates are further distinguished by their broad phlyogenetic distribution; hence it has been suggested that unrelated eukaryotes must have used similar biochemical strategies to control mineralization. Recent studies have shown that an amorphous calcium carbonate (ACC) phase potentially plays a key role in the initial formation of carbonate minerals and in "shaping" them into complex morphologies widely seen in biominerals. Echinoderms, mollusks, and possibly many other organisms use ACC as a precursor phase that is first nucleated in cellularly controlled environments such as vesicles and subsequently transforms into a fully crystalline material. Recent studies on sea urchin embryos have shown that during transformation ACC develops short range that resembles calcite before fully crystallizing and serve as inspiration for our studies in synthetic systems. Self-assembled monolayers (SAM) on gold and silver have been used as simple model systems that approximate biological surfaces. Many studies have shown that thiol monolayers with hydroxyl termination stabilize a transitory ACC film that with prolonged exposure to aqueous solution transforms into calcite nucleated on {104} faces. Using Near Edge X-ray Absorption Fine Structure (NEXAFS) we studied SAM/mineral interactions with well ordered mercaptophenol monolayers showed that when these films are first exposed to calcium carbonate solutions, they become disordered and remain so after subsequent deposition of an ACC over-layer. Yet calcite nucleates and grows from the surface bound ACC with predominantly {104} orientation, which suggests a dynamic structural relationship between the SAMs and the mineral phase. While the monolayer/mineral phase interaction has been characterized, the mechanism for nucleating calcite from ACC on these SAMs remains unknown and is the objective of this research. Our preliminary observations of the transforming ACC film with in situ Raman spectroscopy have shown a strengthening of the symmetric mode of the carbonate ion suggesting ordering of the ACC. To fully determine the structural evolution of the mineral phase we will use both Raman and Extended X-Ray Absorption Fine Structure (EXAFS) measurements, coupled with morphological analysis using SEM.

  19. The Seed Biology Place

    NSDL National Science Digital Library

    Leubner, Gerhard

    2012-02-10

    This remarkable site was created by Professor Gerhard Leubner and his colleagues at the University of Freiburg in Germany. Here, visitors can take advantage of a veritable cornucopia of reference materials related to seed biology, such as diagrams and illustrations of seed germination, plant hormones, endosperm weakening, and seed dormancy. Neophytes may wish to start by looking at the Seed Structure and Anatomy area, which features a concise and well-written overview of the structure, anatomy, and morphology of mature seeds. The same section contains information on the seed structure of the castor bean and other legumes. Another fascinating section on the site is dedicated to Seed Evolution. Visitors can discover a wealth of information here, including such topics as the evolutionary trends of angiosperm seeds and the seed ferns of the Late Permian period. All told, the site is a wonderful resource, and visitors will want to share it with friends.

  20. 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 AH 3.2 by adding NaOH, to form biphasic, micro-, and macroporous calcite-apatitic calcium phosphate (Ap-stoichiometric, apatitic calcium phosphate (Ap-CaP) with a large and reactive surface area of 100­ 200 m2 /g.23 Bone

  1. Petrography and geochemistry of vein-filling calcites, balcones fault zone, upper cretaceous strata, north-central Texas

    SciTech Connect

    Dawson, W.C.; Szymczyk, H.M. [Texaco, Inc., Houston, TX (United States); Reaser, D.F. [Univ. of Texas, Arlington, TX (United States)

    1994-12-31

    The Austin Chalk and the underlying Eagle Ford Shale are transected by en echelon faults and fractures, associated with the Balcones Fault Zone, along an outcrop trend that extends from Dallas to Austin, Texas. These faults and fractures strike generally northeastward, and many are cemented by sparry calcite. Slickensides, preserved on outer surfaces of calcite cements, record fault movement. Early calcite cements are nonferroan, and later cements are ferroan calcite. Petrographic analyses indicate the occurrence of fir-tree zoning and fluorescent inclusions within calcite cements. Vein-filling cements have stable isotopic signatures {delta}{sup 18}O -5.7 to -9.8% PDB; {delta}{sup 13}C +1.6 to +2.7% PDB that are markedly depleted in {delta}{sup 18}O relative to the chalk matrix, inoceramid shells, and the estimated value for Cretaceous seawater. The depleted {delta}{sup 18}O signatures of the vein-filling calcites are suggestive of precipitation from warm basinal fluids. {delta}{sup 13}C analyses reveal that the Austin Chalk buffered the carbon incorporated into the calcite cements. These veins probably formed by a {open_quotes}crack-seal mechanism{close_quotes}, whereby episodic increases in hydropressure caused fracturing. Precipitation of calcite cements within fractures is induced by subsequent decreases in pore pressure. Tectonic and diagenetic features in these outcrops provide analogs for fractured Austin Chalk reservoirs.

  2. The solubility of calcite and aragonite in seawater of 35%. salinity at 25°C and atmospheric pressure

    Microsoft Academic Search

    John W. Morse; Alfonso Mucci; Frank J. Millero

    1980-01-01

    The solubilities of synthetic, natural and biogenic aragonite and calcite, in natural seawater of 35%. salinity at 25°C and 1 atm pressure, were measured using a closed system technique. Equilibration times ranged up to several months. The apparent solubility constant determined for calcite of 4.39(±0.20) × 10 -7 mol 2 kg -2 is in good agreement with other recent solubility

  3. 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

  4. Crystallization in solid solution-aqueous solution systems: Thermodynamic and kinetic approaches

    NASA Astrophysics Data System (ADS)

    Shtukenberg, A. G.; Punin, Yu. O.; Azimov, P. Ya.

    2010-03-01

    A new phenomenological approach is proposed to describe the crystallization kinetics in solid solution-aqueous solution binary systems. The phase diagrams, equilibria, and quasie-quilibria are considered within this approach. The crystallization kinetics near the true equilibrium and the crystallization features at large deviations from equilibrium are discussed on this basis. Special attention is paid to possible interactions in a solution with a seed crystal placed in it. In particular, the interactions leading to the seed’s crystal growth or dissolution and to a possible exchange or metasomatic reactions are considered. In addition, the effect of the generated mismatch stress on the crystal growth rate and composition is analyzed.

  5. 7 CFR 201.18 - Other agricultural seeds (crop seeds).

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ...2014-01-01 2014-01-01 false Other agricultural seeds (crop seeds). 201.18 Section 201.18 Agriculture Regulations...DEPARTMENT OF AGRICULTURE (CONTINUED) FEDERAL SEED ACT FEDERAL SEED ACT REGULATIONS Labeling...

  6. 7 CFR 201.18 - Other agricultural seeds (crop seeds).

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ...2011-01-01 2011-01-01 false Other agricultural seeds (crop seeds). 201.18 Section 201.18 Agriculture Regulations...DEPARTMENT OF AGRICULTURE (CONTINUED) FEDERAL SEED ACT FEDERAL SEED ACT REGULATIONS Labeling...

  7. 7 CFR 201.18 - Other agricultural seeds (crop seeds).

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ...2013-01-01 2013-01-01 false Other agricultural seeds (crop seeds). 201.18 Section 201.18 Agriculture Regulations...DEPARTMENT OF AGRICULTURE (CONTINUED) FEDERAL SEED ACT FEDERAL SEED ACT REGULATIONS Labeling...

  8. 7 CFR 201.18 - Other agricultural seeds (crop seeds).

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...2010-01-01 2010-01-01 false Other agricultural seeds (crop seeds). 201.18 Section 201.18 Agriculture Regulations...DEPARTMENT OF AGRICULTURE (CONTINUED) FEDERAL SEED ACT FEDERAL SEED ACT REGULATIONS Labeling...

  9. 7 CFR 201.18 - Other agricultural seeds (crop seeds).

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ...2012-01-01 2012-01-01 false Other agricultural seeds (crop seeds). 201.18 Section 201.18 Agriculture Regulations...DEPARTMENT OF AGRICULTURE (CONTINUED) FEDERAL SEED ACT FEDERAL SEED ACT REGULATIONS Labeling...

  10. Seed Dispersal: Animals

    NSDL National Science Digital Library

    Pulse of the Planet

    2007-08-02

    The guest scientist in this two-minute radio program discusses seed dispersal in plants. He first explains why it is important for seeds to be distributed away from the mother plant. Then he contrasts wind-dispersed seeds with animal-dispersed seeds, pointing out that animals can disperse larger seeds that contain more nutrients for an emerging seedling. The program, which is available here in audio and text, is part of a Pulse of the Planet series on seed dispersal. Copyright 2005 Eisenhower National Clearinghouse

  11. Growth of bulk GaN crystal by Na flux method

    NASA Astrophysics Data System (ADS)

    Mori, Yusuke; Imade, Mamoru; Maruyama, Mihoko; Yoshimura, Masashi

    2014-03-01

    With current technologies, dislocation-free bulk shape GaN crystals with centimeter-size can be grown from small seed crystals. This technique can be realized by putting a sapphire plate with a small hole (0.5~1.5 mm in diameter) on a GaN plate seed. Centimeter-sized bulk GaN single crystals with large dislocation-free areas could be fabricated by this technique. Cathodoluminescence measurement at the interface between the seed and the grown crystal has revealed that almost all dislocations propagated from the GaN seed were bent and terminated at the initial growth stage. To enlarge the diameter of bulk shape GaN crystals, we have developed the coalescence of GaN crystals from many isolated small seeds. As a first step, we grew two GaN point seeds and coalesced them. Two GaN point seeds were established by mounting a sapphire plate with two small holes. We have found the two GaN crystals grown from two separate seed area coalesced without generating dislocations at a coalescence boundary. The grown GaN crystal can remove from substrate easily during the growth. This phenomenon is effective to reduce the stress in the grown GaN crystal. 2-inch GaN crystals by the coalescence technique. Some of the crystals have very large curvature radius (~100 m).

  12. Vein-filling calcites (petrography and geochemistry): Balcones fault zone, Upper Cretaceous outcrops, north-central Texas

    SciTech Connect

    Dawson, W.C.; Szymczyk, H.M. [Texaco, Inc., Houston, TX (United States); Reaser, D.F. [Univ. of Texas, Arlington, TX (United States)

    1994-09-01

    The Austin Chalk and the underlying Eagle Ford Shale are transacted by en echelon faults and fractures, associated with the Balcones fault zone, along an outcrop trend that extends from Dallas to Austin, Texas. These faults and fractures strike northeastward (N35{degrees} to 40{degrees}E) and are cemented by multiple generations of sparry calcite. Vein widths range from 0.1 to 45 cm. Slickensides, preserved on outer surfaces of calcite cements, record fault movement. Inclusions of country rock are present within calcite-filled veins, and rarely, open fracture porosity is observed in outcrop. Early calcite cements are nonferroan and later cements are ferroan calcite. Petrographic analyses indicate the occurrence of {open_quotes}fir-tree{close_quotes} zoning and fluorescent inclusions within calcite cements. Vein-filling cements have stable isotopic signatures ({delta}{sup 18}O-6.3 to -9.8{per_thousand} PDB; {delta}{sup 13}C +1.6 to +2.5{per_thousand} PDB) that are markedly depleted in {delta}{sup 13}O relative to the chalk matrix, inoceramid shells, and the estimated value for Cretaceous seawater. Trace element analyses indicate the presence of strontium (980-1600 ppm), manganese (750-1975 ppm), zinc (10-20 ppm), and copper (5-10 ppm) in the calcite cements. The negative {delta}{sup 18}O signatures of the vein-filling calcites are suggestive of precipitation from warm fluids. {delta}{sup 13}C analyses reveal that the Austin Chalk buffered the carbon incorporated into the calcite cements. These veins probably formed by a {open_quotes}crack-seat mechanism{close_quotes} whereby episodic increases in hydropressure caused fracturing. Precipitation of calcite cements within fractures is induced by subsequent decreases in pore pressure. Tectonic and diagenetic features in these outcrops provide analogs for fractured Austin Chalk reservoirs.

  13. Zonation and geochemical patterns of burial calcite cements: Upper Smackover Formation, Clarke County, Mississippi

    SciTech Connect

    Heydari, E.; Moore, C.H. (Louisiana State Univ., Baton Rouge (United States))

    1993-01-01

    Cathodoluminescence (CL), trace element concentrations, and isotope compositions of luminescently zoned poikilitic and mosaic calcite cements of the upper Smackover Formation are studied in the Harmony, Pachuta Creek, East Nancy, Goodwater, and Garland Creek fields in Clarke County, Mississippi. These calcites precipitated during burial in a depth range of 100 m to 3 km, a temperature range of 30-100 C, and a time span of 60 my. The calcium carbonate for calcite cementation was primarily derived locally by pressure dissolution of the Smackover Formation. Magnesium content of all calcites ranges from about 500-1,000 ppm in the oldest zones and increases to about 3,000-4,000 ppm toward the younger zones. The low Mg[sup 2+] content of the older zones is the result of precipitation from waters with low Mg[sup 2+]/Ca[sup 2+] ratio, typical of subsurface waters. The increase in Mg[sup 2+] toward the younger zones may have resulted from precipitation over time at progressively higher temperatures and the increase in D[sub Mg[sup 2

  14. Inferences of paleoenvironment from petrographic, chemical and stable-isotope studies of calcretes and fracture calcites

    SciTech Connect

    Vaniman, D.T. [Los Alamos National Lab., NM (United States); Whelan, J.F. [Geological Survey, Denver, CO (United States)

    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.

  15. Calcite and aragonite seas and the de novo acquisition of carbonate skeletons.

    PubMed

    Porter, S M

    2010-09-01

    A longstanding question in paleontology has been the influence of calcite and aragonite seas on the evolution of carbonate skeletons. An earlier study based on 21 taxa that evolved skeletons during the Ediacaran through Ordovician suggested that carbonate skeletal mineralogy is determined by seawater chemistry at the time skeletons first evolve in a clade. Here I test this hypothesis using an expanded dataset comprising 40 well-defined animal taxa that evolved skeletons de novo in the last 600 Myr. Of the 37 taxa whose mineralogy is known with some confidence, 25 acquired mineralogies that matched seawater chemistry of the time, whereas only two taxa acquired non-matching mineralogies. (Ten appeared during times when seawater chemistry is not well constrained.) The results suggest that calcite and aragonite seas do have a strong influence on carbonate skeletal mineralogy, however, this appears to be true only at the time mineralized skeletons first evolve. Few taxa switch mineralogies (from calcite to aragonite or vice versa) despite subsequent changes in seawater chemistry, and those that do switch do not appear to do so in response to changing aragonite-calcite seas. This suggests that there may be evolutionary constraints on skeletal mineralogy, and that although there may be increased costs associated with producing a mineralogy not favored by seawater, the costs of switching mineralogies are even greater. PMID:20550583

  16. 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.

  17. Particle characteristics and their influence on dewatering of kaolin, calcite and quartz suspensions

    Microsoft Academic Search

    L. Besra; D. K. Sengupta; S. K. Roy

    2000-01-01

    The effect of particle properties and dispersion on the filtration and dewatering behaviour of three different minerals namely kaolin, calcite and quartz in aqueous media have been examined. The primary particle properties such as particle size, size distribution, specific surface area, density, surface structure, dry bed porosities and sphericities of particles as well as their dispersion properties like solid concentration,

  18. Assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures

    Microsoft Academic Search

    Dirk Nürnberg; Jelle Bijma; Christoph Hemleben

    1996-01-01

    Though many studies on the Mg contents in the calcitic tests of foraminifers exist, the processes controlling its uptake are still a matter of debate. Laboratory cultures offer an excellent opportunity to reveal these mechanisms. The Mg concentrations within single chambers of the planktic foraminifer Globigerinoides sacculifer (BRADY) maintained under controlled laboratory conditions were measured (1) at variable temperatures (19.5–29.5

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

    E-print Network

    Hacker, Bradley R.

    mechanisms, and rates Bradley R. Hacker,1 David C. Rubie,2 Stephen H. Kirby,3 and Steven R. Bohlen4 Received in Japan and China that disproportionated to low-Mg calcite and dolomite. Citation: Hacker, B. R., D. C starting material is a single block of Carrara marble obtained from a monument company [Hacker and Kirby

  20. Temperature Dependence of1 Oxygen Isotope Fractionation in Coccolith Calcite:2

    E-print Network

    Paris-Sud XI, Université de

    Temperature Dependence of1 Oxygen Isotope Fractionation in Coccolith Calcite:2 A Culture and Core isotopic effect or vital effect . The direction of fractionation towards light39 isotopic values was significantly closer to equilibrium compared to previously reported offset values. No41 significant isotopic

  1. Calcite precipitation in Lake Constance: Chemical equilibrium, sedimentation,and nucleation by algae

    Microsoft Academic Search

    H.-H. STABEL

    1986-01-01

    Seasonal shifts in calcium carbonate solution equilibria in the limnetic zone of Lake Constance were documented between 1981 and 1983. Except during mixing times, lake water was supersat- urated with respect to calcite; epilimnetic supersaturation maxima were closely related to changes in pH. Sedimentation of calcium from the lower boundary of the euphotic zone to the lake bottom was also

  2. Inferences of paleoenvironment from petrographic, chemical and stable-isotope studies of calcretes and fracture calcites

    SciTech Connect

    Vaniman, D.T. [Los Alamos National Lab., NM (United States); Whelan, J.F. [Geological Survey, Denver, CO (United States)

    1994-12-31

    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 {open_quotes}plug{close_quotes}. 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.

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

    E-print Network

    Elliott, James

    , an understand- ing of the chemical and physical properties of calcium car- bonate polymorphs, especially calcite greenhouse effect and climate change where it is used as an isotope counter4 , and as a catalyst in solvent these problems and has been used extensively to study calcium carbonate in a wide variety of situations

  4. NMR surface relaxivity of calcite with adsorbed Mn{sup 2+}

    SciTech Connect

    Kenyon, W.E.; Kolleeny, J.A. [Schlumberger-Doll Research, Ridgefield, CT (United States)] [Schlumberger-Doll Research, Ridgefield, CT (United States)

    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.

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

    E-print Network

    Dysthe, Dag Kristian

    -and-valley structure in a (near-)saturated solution so as to lower its total surface free energy in spite of a larger of crys- tals and hence their solubility in aqueous solutions (Pater- son, 1973). A significant increase, and at depth, dissolution and precipitation of calcite underlie processes such as pres- sure solution

  6. 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.

  7. Permeability of calcite-cemented fractures in mudrocks: Flow highway or hindrance?

    NASA Astrophysics Data System (ADS)

    Landry, C. J.; Eichhubl, P.; Prodanovic, M.; Tokan-Lawal, A.

    2014-12-01

    Among natural fractures observed in core of Eagle Ford Shale, Texas, tall sub-vertical calcite-cemented fractures are the most spatially extensive. Similar sub-vertical opening-mode fractures are found in many mudrocks, and far more often than not they are completely cemented. Currently there is very little evidence that these calcite cements are anything but impermeable, and thus would hinder flow across the fractures while having an insignificant effect on flow parallel to the fractures. This suggests that natural fractures in mudrocks are barriers to flow, which goes against the general consensus that natural fractures in mudrocks enhance flow. We used scanning-electron microscopy (SEM) on broad-beam argon-ion milled samples of a calcite-cemented fracture with a kinematic aperture (width) of 200 ?m to study the pore space of the calcite for any indication that completely cemented fractures are permeable. In the fracture calcite cement, we observed primary porosity between calcite grains that is generally well-connected with an average aperture between 25 and 100 nm. The permeability of these flow-paths was determined by lattice Boltzmann methods to be between 50 to 200 ?D. These flow-paths have a spacing between 50 and 300 ?m, therefore a square centimeter (length*height) of fracture cement will contain on average more than 100 flow-paths. Thus for flow across the fracture cement (orthogonal to the fracture) the overall cross-fracture permeability of the cement can be approximated using simple effective medium upscaling. The fracture cement studied here is found to have a cross-fracture permeability in the range of 25 to 100 nD. Although this is a very low permeability, it is within the range of the permeability of the host rock, and thus these calcite cements would have almost no effect on flow orthogonal to the plane of the fracture. These flow-paths are also connected within the cement creating the equivalent of a single tortuous flow-path along the plane of the fracture with a possible permeability upwards of 10 to 50 ?D. This is far lower than the permeability of the fracture without the cement (~1500 D), but in comparison to the host rock permeability (< 200 nD) would still act as a highway for fluid flow.

  8. Evaluation of Sierra Nevada seeding effects on snowfall processes and distribution. Final report, 1 July 1988-30 June 1989

    Microsoft Academic Search

    Warburton

    1990-01-01

    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.

  9. Inside a Seed

    NSDL National Science Digital Library

    2007-12-12

    This image from Biology by Kenneth R. Miller and Joseph Levine illustrates the five most important parts of a seed: the seed coat, the endosperm, and the embryos primary root, cotyledon, and embryonic leaves.

  10. Calcite saturation state effects on cultured benthic foraminiferal trace-element distribution coefficients

    NASA Astrophysics Data System (ADS)

    Hintz, C. J.; Shaw, T. J.; Chandler, G. T.; McCorkle, D. C.; Bernhard, J. M.; Blanks, J. K.

    2006-12-01

    Field studies have suggested that calcite saturation states (Ømega) near and below saturation alter trace element distribution coefficients in benthic foraminifera. Recent benthic foraminiferal culture experiments at the University of South Carolina investigated the response of trace element signatures to three different calcite saturation seawater environments by manipulating total alkalinity (TA). Starting with near-surface Gulf Stream water (Ømega = 3, TA=2380 ?eq kg-1), two seawater reservoirs were titrated with HCl to lower their calcite saturation states (Ømega = 2, TA = 1910 ?eq kg-1; Ømega = 1.1, TA = 1320 ?eq kg-1). Mixed-species foraminiferal assemblages, with the calcite-specific fluorescent label calcein, were inoculated into 13 total culture chambers evenly distributed among the control and 2 treatment seawater reservoirs. These cultures were maintained at 7.2 ± 0.1 °C temperature and 36.6 ± 0.4 ‰ salinity for 8 months. Total alkalinity and dissolved inorganic carbon, measured biweekly, characterized the carbonate system and verified that the calcite saturation state remained stable over the culture duration. Trace element concentrations were also measured biweekly. Foraminiferal reproduction ( Bulimina marginata) was observed in each seawater chemistry. These individuals were utilized for trace element and stable isotope (data not presented here) analysis. Additionally, terminal chambers precipitated in alkalinity-adjusted cultures were identified by the absence of the pre-culture calcein label used on all inoculated foraminifera. These cultured chambers were separated by laser microdissection and analyzed for trace element content by isotope dilution inductively-coupled plasma mass spectrometry. We present the initial results of these trace element distribution coefficients measured in cultured benthic foraminifera from three different Ømega. This research was funded by National Science Foundation grants OCE-0351029 and OCE-0437366.

  11. High resolution record of Holocene climate change in speleothem calcite from Cold Water Cave, northeast Iowa

    SciTech Connect

    Dorale, J.A.; Gonzalez, L.A.; Reagan, M.K. (Univ. of Iowa, Iowa City, IA (United States). Dept. of Geology); Pickett, D.A.; Murrell, M.T. (Los Alamos National Lab., NM (United States)); Baker, R.G. (Univ. of Iowa, Iowa City, IA (United States))

    1992-01-01

    High-precision Uranium-Thorium mass spectrometric chronology and O-18--C-13 isotopic analysis of speleothem calcite from Cold Water Cave in northeast iowa have been used to chart mid-Holocene climate change in the North American Midcontinent. Significant shifts in stalagmite [delta]O-18 and [delta]C-13 at 5,900 and 3,600 years BP coincide with well documented Holocene vegetation changes. Estimates of mean annual temperature have been made using stalagmite calcite [delta]O-18 to constrain an iterative solution for temperature in an equation combining, Dansgaard's (1964) precipitation-temperature relationship and Friedman and O'Neils (1977) fractionation relationship. Temperature estimates suggest a rapid warming of approximately 3 C at 5,900 years BP, followed by a rapid 4 C cooling at 3,600 years BP. The initiation of a gradual increase in calcite [delta]C-13 at 5,900 years BP suggests that replacement of forest (C[sub 3] rich) dominated soil biomass by prairie detritus (C[sub 4] rich) is slow. Biomass turnover is not complete by 3,600 years BP when rapid cooling and a return to forest dominated vegetation takes place. The preserved record in stalagmite calcite provides a more precise and accurate timing of climatic change for the North American Midcontinent than those obtained from C-14 dated records such as pollen and plant macrofossil. Continuous deposition of stalagmite calcite could potentially allow the extraction of better than decadal and possibly annual climate record during the Holocene.

  12. Rheology of calcite-quartz aggregates deformed to large strain in torsion

    NASA Astrophysics Data System (ADS)

    Rybacki, Erik; Paterson, Mervyn S.; Wirth, Richard; Dresen, Georg

    2003-02-01

    High-temperature, high-pressure torsion experiments have been conducted on Solnhofen limestone and synthetic calcite-quartz aggregates to investigate the evolution of mechanical strength and microstructure to large strains. Hot isostatic pressing of powders containing 1-30 wt% quartz particles produced synthetic two-phase aggregates containing trace amounts of wollastonite. The experiments were performed at constant twist rate, 300 MPa confining pressure, and temperatures ranging from 900 to 1300 K in the stability fields of calcite plus quartz and wollastonite plus carbon dioxide. The mechanical data from torsion tests of most samples show a pronounced peak stress at shear strains <1 and subsequent weakening. For most samples, a steady state stress is reached only at shear strains >5. A distinct shape and lattice preferred orientation developed in Solnhofen limestone and in the calcite matrix of the synthetic aggregates. However, at large shear strains, flattened porphyroclasts were almost entirely consumed by recrystallization. Elongation parallel to the specimen axis at temperature below 1100 K is possibly due to rotation of minerals into a preferred crystallographic orientation. Stress exponent and activation energy for creep of the calcite-quartz aggregates increase substantially with increasing quartz content. The strength of the two-phase aggregates increases with quartz fraction up to 20 wt% by a factor of 2-5 depending on temperature and finite strain. Continuum models underestimate particle strengthening of the calcite-quartz aggregates. An alternative microphysical mechanism for the observed strengthening may be related to the reduced mobility of dislocations through diffusion of silicon into dislocation cores.

  13. 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.

  14. Stimulated Raman scattering of the second harmonic of a neodymium laser in nitrate crystals

    Microsoft Academic Search

    A S Eremenko; S N Karpukhin; A I Stepanov

    1980-01-01

    An investigation was made of the efficiency of stimulated Raman scattering in sodium, barium, and lead nitrates, compared with that in calcite. Measurements were made of the energies of two Stokes components of stimulated Raman scattering. The suitability of nitrate crystals for Raman stimulated emission was demonstrated.

  15. SEED Database Requirements

    Microsoft Academic Search

    Robert Coyne; Robert Woodbury; Shang-Chia Chiou; Bongjin Choi; Han Kiliccote; Teng-Weng Chang; Sheng-Fen Chien; Jim Snyder

    SEED is an acronym for Software Environment to Support the Early Phases in Building Design. The overall architecture of SEED is based on a division of the preliminary design process into phases, each of which addresses a specific task. SEED intends to support each phase by an individual support module based on a shared logic and architecture. The modules envisioned

  16. What Are Chia Seeds?

    MedlinePLUS

    ... diet? Chia seeds come from the desert plant Salvia hispanica , a member of the mint family. Salvia hispanica seed is often sold under its common ... Aztec diet. The seeds of a related plant, Salvia columbariae (golden chia), were used primarily by Native ...

  17. 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.

  18. Seeding effects on solidification behavior of cocoa butter and dark chocolate. I. Kinetics of solidification

    Microsoft Academic Search

    Iwao Hachiya; Tetsuo Koyano; Kiyotaka Sato

    1989-01-01

    Effects of seeding of fat crystals on the crystallization kinetics of cocoa butter and dark chocolate were examined with a\\u000a rotational viscometer. The seed crystals employed were cocoa butter, 1,3-distearoyl-2-oleoylglycerol (SOS), 1,3-dibehenoyl-2-oleoylglycerol\\u000a (BOB) and 1,2,3-tristearoylglycerol (SSS). The seed powders were prepared by pulverization below —50?C, the dimensions being\\u000a in a range from 20–70 ?m. Particular attention was paid to the

  19. 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.

  20. 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

  1. Calibration of the calcite-water oxygen-isotope geothermometer at Devils Hole, Nevada, a natural laboratory

    USGS Publications Warehouse

    Coplen, T.B.

    2007-01-01

    The ??18O of ground water (-13.54 ?? 0.05 ???) and inorganically precipitated Holocene vein calcite (+14.56 ?? 0.03 ???) from Devils Hole cave #2 in southcentral Nevada yield an oxygen isotopic fractionation factor between calcite and water at 33.7 ??C of 1.02849 ?? 0.00013 (1000 ln ??calcite-water = 28.09 ?? 0.13). Using the commonly accepted value of ???(??calcite-water)/???T of -0.00020 K-1, this corresponds to a 1000 ln ??calcite-water value at 25 ??C of 29.80, which differs substantially from the current accepted value of 28.3. Use of previously published oxygen isotopic fractionation factors would yield a calcite precipitation temperature in Devils Hole that is 8 ??C lower than the measured ground water temperature. Alternatively, previously published fractionation factors would yield a ??18O of water, from which the calcite precipitated, that is too negative by 1.5 ??? using a temperature of 33.7 ??C. Several lines of evidence indicate that the geochemical environment of Devils Hole has been remarkably constant for at least 10 ka. Accordingly, a re-evaluation of calcite-water oxygen isotopic fractionation factor may be in order. Assuming the Devils Hole oxygen isotopic value of ??calcite-water represents thermodynamic equilibrium, many marine carbonates are precipitated with a ??18O value that is too low, apparently due to a kinetic isotopic fractionation that preferentially enriches 16O in the solid carbonate over 18O, feigning oxygen isotopic equilibrium.

  2. A reaction-transport model for calcite precipitation and evaluation of infiltration fluxes in unsaturated fractured rock.

    PubMed

    Xu, Tianfu; Sonnenthal, Eric; Bodvarsson, Gudmundur

    2003-06-01

    The percolation flux in the unsaturated zone (UZ) is an important parameter addressed in site characterization and flow and transport modeling of the potential nuclear-waste repository at Yucca Mountain, NV, USA. The US Geological Survey (USGS) has documented hydrogenic calcite abundances in fractures and lithophysal cavities at Yucca Mountain to provide constraints on percolation fluxes in the UZ. The purpose of this study was to investigate the relationship between percolation flux and measured calcite abundances using reactive transport modeling. Our model considers the following essential factors affecting calcite precipitation: (1) infiltration, (2) the ambient geothermal gradient, (3) gaseous CO(2) diffusive transport and partitioning in liquid and gas phases, (4) fracture-matrix interaction for water flow and chemical constituents, and (5) water-rock interaction. Over a bounding range of 2-20 mm/year infiltration rate, the simulated calcite distributions capture the trend in calcite abundances measured in a deep borehole (WT-24) by the USGS. The calcite is found predominantly in fractures in the welded tuffs, which is also captured by the model simulations. Simulations showed that from about 2 to 6 mm/year, the amount of calcite precipitated in the welded Topopah Spring tuff is sensitive to the infiltration rate. This dependence decreases at higher infiltration rates owing to a modification of the geothermal gradient from the increased percolation flux. The model also confirms the conceptual model for higher percolation fluxes in the fractures compared to the matrix in the welded units, and the significant contribution of Ca from water-rock interaction. This study indicates that reactive transport modeling of calcite deposition can yield important constraints on the unsaturated zone infiltration-percolation flux and provide useful insight into processes such as fracture-matrix interaction as well as conditions and parameters controlling calcite deposition. PMID:12744832

  3. Oxygen isotope relationships between rainfall, dripwater and speleothem calcite from Westcave, central Texas, USA: Possible implications for paleoclimate study

    NASA Astrophysics Data System (ADS)

    Heinze Fry, A. L.; FENG, W.; Banner, J. L.; Casteel, R. C.

    2011-12-01

    Paleoclimate conditions such as temperature and rainfall amount can be inferred from oxygen isotope (?18O) records of speleothems. Understanding the environmental controls on oxygen isotope variations in speleothem calcite will improve such inferences. Westcave preserve, located in central Texas, contains a small, shallow, and well-ventilated cave where year-round speleothem growth is primarily influenced by temperature, which ranges up to 20 °C seasonally. This provides an opportunity to examine the relationships between temperature and rainfall, dripwater and speleothem calcite ?18O as a means to assess speleothem ?18O as a paleoclimate proxy. Over the study period from April 2009 to June 2011, rainfall ?18O values ranged from -10.5 to 1.0 % (VSMOW), whereas dripwater ?18O values ranged from -4.8 to -3.9 % (VSMOW). The small range of 1.1 % in dripwater ?18O, compared to a rainfall ?18O range of 11.5 %, indicates a well-homogenized water reservoir feeding the Westcave speleothems. Calcite grown on a sequence of artificial substrates placed under three active drip sites in the cave has ?18O values ranging from 6.6 to -3.1 % (PDB). When compared to expected ?18O of calcite in equilibrium with its associated dripwater (calculated using measured cave temperatures and published calcite-water oxygen isotope fractionation factors), measured calcite ?18O are either in isotope equilibrium, or deviate from it up to 2.0 %, indicating possible influence of kinetic fractionation. Nevertheless, the 3.5 % seasonal variation in ?18O values of substrate calcite displays a strong negative correlation with temperature, including water temperature, cave air temperature and outside air temperature from a nearby weather station. These correlations, along with relatively narrow seasonal range in dripwater ?18O values, indicate that temperature is the most important factor controlling speleothem calcite ?18O in this setting, allowing for the potential preservation of seasonal temperature variations in speleothem calcite from this cave.

  4. Controlled crystallization of emerald from the fluxed melt

    Microsoft Academic Search

    S. N Barilo; G. L Bychkov; L. A Kurnevich; N. I Leonuk; V. P Mikhailov; S. V Shiryaev; V. T Koyava; T. V Smirnova

    1999-01-01

    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

  5. Influence of He-Ne laser irradiation of soybean seeds on seed mycoflora, growth, nodulation, and resistance to Fusarium solani.

    PubMed

    Ouf, S A; abdel-Hady, N F

    1999-01-01

    Laser irradiation of soybean seeds for 3 min caused a clear reduction in the number of seed-borne fungi which became more pronounced as the irradiation time was extended. Pretreatment of the seeds with methylene blue, methyl red and carmine enhanced the effect of laser. Rhizoctonia solani, Alternaria tenuissima, Cercospora kikuchii and Colletotrichum truncatum were completely eliminated when the seeds were pretreated with a dye and irradiated for 10 min. Seed germination was stimulated on exposure of the seed to 1-min irradiation. At such dose, most of the dyes were accelerators while the higher doses were inhibitory to seed germination. Chlorophyll a, chlorophyll b and carotenoid content of developed plants differed, depending on the irradiation dose and dye treatment of the seeds. In seeds irradiated for 1 or 3 min, chlorophyll a formation was less affected than chlorophyll b formation. In seeds irradiated for 10 min, both the chlorophyll contents were decreased especially in the presence of some applied dyes. On the other hand, there was an increase in carotenoid content of soybean leaves when the laser dose increased. The number and dry mass of nodules were mostly greater (as compared to the corresponding control), when the seeds irradiated for 1 or 3 min were pretreated with methyl red, chlorophenol red, crystal violet and methylene blue. Irradiation of pre-sowing seeds greatly protected soybean stands against F. solani. The disease incidence differed somewhat when the irradiated seeds were pretreated with dyes. The reduction in disease incidence was accompanied by accumulation of high proline and phenol levels in the infected root tissues of soybean, suggesting that these compounds have a certain role in the prevention of disease development. PMID:10983234

  6. A thermodynamic adsorption/entrapment model for selenium(IV) coprecipitation with calcite

    NASA Astrophysics Data System (ADS)

    Heberling, Frank; Vinograd, Victor L.; Polly, Robert; Gale, Julian D.; Heck, Stephanie; Rothe, Jörg; Bosbach, Dirk; Geckeis, Horst; Winkler, Björn

    2014-06-01

    Selenium is an environmentally relevant trace element, while the radioisotope 79Se is of particular concern in the context of nuclear waste disposal safety. Oxidized selenium species are relatively soluble and show only weak adsorption at common mineral surfaces. However, a possible sorption mechanism for selenium in the geosphere is the structural incorporation of selenium(IV) (selenite, SeO32-) into calcite (CaCO3). In this study we investigate the interactions between selenite and calcite by a series of experimental and computational methods with the aim to quantify selenite incorporation into calcite at standard conditions. We further seek to describe the thermodynamics of selenite-doped calcite, and selenite coprecipitation with calcite. The structure of the incorporated species is investigated using Se K-edge EXAFS (isotropic and polarization dependent) and results are compared to density functional theory (DFT) calculations. These investigations confirm structural incorporation of selenite into calcite by the substitution of carbonate for selenite, leading to the formation of a Ca(SeO3)X(CO3)(1-X) solid solution. Coprecipitation experiments at low supersaturation indicate a linear increase of the selenite to carbonate ratio in the solid with the increase of the selenite to carbonate ratio in the contact solution. This relationship can be described under the assumption of an ideal mixing between calcite and a virtual CaSeO3 endmember, whose standard Gibbs free energy (G0(CaSeO3_exp) = -953 ± 6 kJ/mol, log10(KSP(CaSeO3_exp)) = -6.7 ± 1.0) is defined by linear extrapolation of the excess free energy from the dilute Henry’s law domain to X(CaSeO3) = 1. In contrast to this experimental result, DFT and force field calculations predict the virtual bulk CaSeO3 endmember to be significantly less stable and more soluble: G0(CaSeO3 bulk) = -912 ± 10 kJ/mol and log10(KSP(CaSeO3_bulk)) = 0.5 ± 1.7. To explain this discrepancy we introduce a thermodynamic adsorption/entrapment concept. This concept is based on the idea that the experimental value of -953 ± 6 kJ/mol reflects the Gibbs free energy of CaSeO3 within the surface layer, while the value obtained from atomistic calculations reflects bulk thermodynamic properties. In coprecipitation experiments performed at steady-state conditions the difference between these values is compensated by the supersaturation. Thus, if the Gibbs free energies of the bulk CaCO3 and CaSeO3 endmembers are substituted with the Gibbs free energies of the surface endmembers, the coprecipitation experiment can still be treated within the formalism of equilibrium thermodynamics. This concept leads to a number of important consequences, which can be tested both experimentally and theoretically. We show that selenite adsorption at the calcite surface and selenite coprecipitation with calcite under supersaturated conditions can be described with the same partition coefficient. This implies that the coprecipitation can be viewed as a sequence of adsorption and entrapment events. On the other hand, our aragonite recrystallization experiments show that at near equilibrium conditions the calcite growth is inhibited in the presence of selenite. Consistent with these observations, our DFT calculations show that the substitution of carbonate for selenite is energetically more favorable at the surface than inside the bulk. The whole set of the experimental and atomistic simulation results leads to the conclusion that the calcite-CaSeO3 solid solution can only grow continuously if the aqueous solution is supersaturated with respect to the bulk solid solution. Under these conditions selenite coprecipitates with calcite at a partition coefficient of D = 0.02 ± 0.01. If the solution is undersaturated with respect to the bulk solid solution, only surface ion-exchange occurs. Elevated selenite concentrations in bulk calcite therefore reflect non-equilibrium conditions.

  7. Precision metering of germinated seeds 

    E-print Network

    Elliot, Gregory Lawrence

    1990-01-01

    Seeds Purpose and Objectives REVIEW OF LITERATURE Precision Planters and Meters for Dry Seeds Trapping Seeds in Cells Trapping Seeds by Air Pressure Using Other Methods for Dry Seeds Planters and Meters for Seeds in Liquid Extruding a Continuous... require only that a certain plant population density be achieved. Willey (1982) points out that this type of crop may be planted with nonprecision planters or broadcast seeders, which control only the rate at which seeds are distributed. However...

  8. Mass-spectrometric 230Th-234U-238U dating of the Devils Hole calcite vein

    USGS Publications Warehouse

    Ludwig, K. R.; Simmons, K.R.; Szabo, B. J.; Winograd, I.J.; Landwehr, J.M.; Riggs, A.C.; Hoffman, R.J.

    1992-01-01

    The Devils Hole calcite vein contains a long-term climatic record, but requires accurate chronologic control for its interpretation. Mass-spectrometric U-series ages for samples from core DH-11 yielded 230Th ages with precisions ranging from less than 1,000 years (2??) for samples younger than ???140 ka (thousands of years ago) to less than 50,000 years for the oldest samples (???566 ka). The 2348U/238U ages could be determined to a precision of ???20,000 years for all ages. Calcite accumulated continuously from 566 ka until ???60 ka at an average rate of 0.7 millimeter per 103 years. The precise agreement between replicate analyses and the concordance of the 230Th/238U and 234U/238U ages for the oldest samples indicate that the DH-11 samples were closed systems and validate the dating technique in general.

  9. Natural variations in calcite dissolution rates in streams: Controls, implications, and open questions

    NASA Astrophysics Data System (ADS)

    Covington, M. D.; Gulley, J. D.; Gabrovšek, F.

    2015-04-01

    Models of bedrock channel evolution typically assume that chemical erosion is negligible in comparison to mechanical erosion. While this assumption is reasonable for channels in silicate rocks, it is questionable within highly soluble strata such as carbonates. The magnitude and variability of calcite dissolution rates in streams has remained as a critical unknown for models of bedrock incision and karst conduit formation. Here we use U.S. Geological Survey data to estimate calcite dissolution rates from 77 different streams located in a wide range of settings. The calculated rates are commonly on the order of ˜1 mmyr-1, which is 1 to 2 orders of magnitude larger than previous estimates. We also find that PCO2 is the strongest control on at-a-site variability, though some sites also display dilution-controlled variability. Typically, dissolution rates vary within a relatively narrow range, which has important implications for the relative importance of chemical and mechanical erosion.

  10. Temperature Effects in ESR Spectra of Radical Centres in Dripstone Calcite Samples Used for ESR Dating

    NASA Astrophysics Data System (ADS)

    Wencka, M.; Hoffmann, S. K.; Krzyminiewski, R.; Mielcarek, S.

    2006-09-01

    Natural calcite samples were collected from the dripstone layers of the Black Cave of the Tatra Mountains. ESR spectra, thermal analysis, and thermoluminescence data were analysed to obtain a consistent picture of the calcite properties. The ESR spectra were analysed using computer enhanced resolution spectra and an influence of the thermal annealing on intensity of individual ESR lines was measured. These results together with the effects of ?-irradiation in ESR spectra allowed one to discriminate between ESR lines from various paramagnetic centres. A general conclusion of the paper is that in the ESR dating the outer ESR lines of CO-3 (g=2.0125) and CO-2 (g=1.9980) radicals should be used instead of the commonly used multicomponent central line.

  11. Infrared Signature of the Cation-? Interaction between Calcite and Aromatic Hydrocarbons.

    PubMed

    Wang, Haitao; Grant, Daniel J; Burns, Peter C; Na, Chongzheng

    2015-06-01

    The cation-? interaction is proposed as an important mechanism for the adsorption of aromatic hydrocarbons having non-zero quadrupole moments by mineral surfaces. Direct evidence supporting such a mechanism is, however, limited. Using the model mineral calcite, we probe the cation-? interaction with adsorbed benzene, toluene, and ethylbenzene (BTE) molecules using attenuated total reflectance Fourier transform infrared spectroscopy. We show that the presence of calcite increases the energy required to excite the synchronized bending of aromatic C-H bonds of BTE molecules. The unique conformation of this vibrational mode indicates that the planar aromatic rings of BTE molecules are constrained in a tilted face-down position by the cation-? interaction, as further confirmed by density functional theory calculations. Our results suggest that the shift of the excitation energy of the aromatic C-H bending may be used as an infrared signature for the cation-? interaction occurring on mineral surfaces. PMID:25974679

  12. Arsenic uptake by gypsum and calcite: Modeling and probing by neutron and x-ray scattering

    E-print Network

    Fernandez-Martinez, Alejandro; Roman-Ross, Gabriela; Johnson, Mark R; Bardelli, Fabrizio; Turrillas, Xavier; Charlet, Laurent

    2006-01-01

    Here we report on two structural studies performed on As-doped gypsum (CaSO4 2H2O) and calcite (CaCO3), using neutron (D20-ILL) and x-ray (ID11-ESRF) diffraction data and EXAFS (BM8-ESRF). The aim of this study is to determine whether As gets into the bulk of gypsum and calcite structures or is simply adsorbed on the surface. Different mechanisms of substitution are used as hypotheses. The combined Rietveld analysis of neutron and x-ray diffraction data shows an expansion of the unit cell volume proportional to the As concentration within the samples. DFT-based simulations confirm the increase of the unit cell volume proportional to the amount of carbonate or sulphate groups substituted. Interpolation of the experimental Rietveld data allows us to distinguish As substituted within the structure from that adsorbed on the surface of both minerals.

  13. On the origin of size-dependent and size-independent crystal growth: Influence of advection and diffusion

    USGS Publications Warehouse

    Kile, D.E.; Eberl, D.D.

    2003-01-01

    Crystal growth experiments were conducted using potassium alum and calcite crystals in aqueous solution under both non-stirred and stirred conditions to elucidate the mechanism for size-dependent (proportionate) and size-independent (constant) crystal growth. Growth by these two laws can be distinguished from each other because the relative size difference among crystals is maintained during proportionate growth, leading to a constant crystal size variance (??2) for a crystal size distribution (CSD) as the mean size increases. The absolute size difference among crystals is maintained during constant growth, resulting in a decrease in size variance. Results of these experiments show that for centimeter-sized alum crystals, proportionate growth occurs in stirred systems, whereas constant growth occurs in non-stirred systems. Accordingly, the mechanism for proportionate growth is hypothesized to be related to the supply of reactants to the crystal surface by advection, whereas constant growth is related to supply by diffusion. Paradoxically, micrometer-sized calcite crystals showed proportionate growth both in stirred and in non-stirred systems. Such growth presumably results from the effects of convection and Brownian motion, which promote an advective environment and hence proportionate growth for minute crystals in non-stirred systems, thereby indicating the importance of solution velocity relative to crystal size. Calcite crystals grown in gels, where fluid motion was minimized, showed evidence for constant, diffusion-controlled growth. Additional investigations of CSDs of naturally occurring crystals indicate that proportionate growth is by far the most common growth law, thereby suggesting that advection, rather than diffusion, is the dominant process for supplying reactants to crystal surfaces.

  14. Uranium-series age determination of calcite veins, VC-1 drill core, Valles Caldera, New Mexico

    NASA Astrophysics Data System (ADS)

    Sturchio, Neil C.; Binz, Carl M.

    1988-06-01

    Uranium-series analysis (238U-234U-230Th) of 13 calcite veins from the hydrothermally altered Madera Limestone in the VC-1 drill core was performed to determine the ages of the veins and their relation to the Valles hydrothermal system. Thermal water from VC-1 and two hot springs in San Diego Canyon was analyzed for U and (234U/238U) to help evaluate the constancy of initial (234U/238U). The (230Th/234U) age of one of the veins is ˜95 kyr, and those of two other veins are ˜230 and ˜250 kyr. Five of the veins have near equilibrium (230Th/234U) and are probably older than ˜0.3 m.y. Uranium concentrations in the remaining veins are too low for analysis by the ?-spectrometry techniques employed in this study. Of the five veins near (230Th/234U) equilibrium, four are also near (234U/238U) equilibrium, suggesting ages greater than ˜1.0 m.y., but one has (234U/238U) = 1.15, suggesting an age between ˜0.3 and ˜1.0 m.y. Calculated initial (234U/238U) of the veins yielding relatively young ages are neither equal to each other nor to (234U/238U) in thermal water from VC-1, indicating inconstancy of initial (234U/238U) that may be related to variations in groundwater mixing proportions. Three of the four veins that yield relatively young ages consist of coarse, sparry, vuggy calcite, suggesting that this may be the type of calcite vein which forms under conditions resembling those encountered presently in VC-1. The analytical data are consistent with closed-system behavior of U and Th in the VC-1 calcite veins.

  15. Arsenic removal from high-arsenic water by enhanced coagulation with ferric ions and coarse calcite

    Microsoft Academic Search

    S. Song; A. Lopez-Valdivieso; D. J. Hernandez-Campos; C. Peng; M. G. Monroy-Fernandez; I. Razo-Soto

    2006-01-01

    Arsenic removal from high-arsenic water in a mine drainage system has been studied through an enhanced coagulation process with ferric ions and coarse calcite (38–74?m) in this work. The experimental results have shown that arsenic-borne coagulates produced by coagulation with ferric ions alone were very fine, so micro-filtration (membrane as filter medium) was needed to remove the coagulates from water.

  16. Laminated Iron Texture by Iron-Oxidizing Bacteria in a Calcite Travertine

    Microsoft Academic Search

    Chizuru Takashima; Akihiro Kano; Takeshi Naganuma; Kazue Tazaki

    2008-01-01

    An iron-rich travertine at Shionoha hot-spring in western Japan, displays a sub-millimetre order lamination consisting of microbially-incduced ferrihydrite and calcite-matrix. The ferrihydrite occurs as 5- to 10-? m thick filaments that extend and apparently branch upwards. A sheathed morphotype having a meshwork of a rod-like organic substance and phylogenetically identified species of genus Siderooxidans were responsible for precipitation of the

  17. Cross dating (Th\\/U- 14C) of calcite covering prehistoric paintings in Borneo

    Microsoft Academic Search

    Valérie Plagnes; Christiane Causse; Michel Fontugne; Hélène Valladas; Jean-Michel Chazine; Luc-Henri Fage

    2003-01-01

    We present the first application of cross-dating (Th\\/U measured by thermo-ionization mass spectrometry (TIMS) and 14C measured by accelerator mass spectrometry (AMS)) of calcite covering prehistoric paintings. Th\\/U age estimates of cave drapery range from 9800 to 27,300 yr B.P. while conventional 14C age is estimated between 9900 and 7610 yr B.P. depending on the dead carbon correction. The age

  18. 13C 12C exchange between calcite and graphite: A possible thermometer in Grenville marbles

    USGS Publications Warehouse

    Valley, J.W.; O'Neil, J.R.

    1981-01-01

    The fractionation of 13C between calcite and graphite, ??(Cc-Gr). is consistently small (2.6-4.8 permil) in 34 assemblages from upper amphibolite- and granulite-facies marbles of the Grenville Province. In 25 samples from the Adirondack Mountains, New York, it decreases regularly with increasing metamorphic temperature. The fractionations are independent of absolute ??13C values of calcite (-2.9 to +5.0). For T = 600-800??C, the Adirondack data are described by ??(Cc-Gr) = -0.00748T (??C) + 8.68. This good correlation between ?? and T suggests that carbon isotope equilibrium was attained in these high-grade marbles and that the theoretical calculations of this fractionation by Bottinga are approximately 2 permil too large in this temperature range. Because of the relatively high temperature sensitivity suggested by these results and by Bottinga's calculations, and the pressure independence of isotope fractionation, ??(Cc-Gr) may provide a very good thermometer for high-grade marbles. Comparison of this field calibration for ??(Cc-Gr) vs temperature with results from other terranes supports the utility of ??(Cc-Gr) for geothermometry and suggests that graphite is much more sluggish to exchange than calcite, that exchange between calcite and graphite occurs at temperatures as low as 300??C, and that equilibrium may normally be attained only when peak metamorphic temperatures are greater than 500-600??C. Because 13C exchange is an unavoidable metamorphic process at temperatures above 300??C, high values of ??13C(Gr) in moderate- to high-grade carbonate-bearing rocks do not provide a sufficient criterion to infer an abiogenic origin for the graphite. ?? 1981.

  19. Partitioning of Sr 2+ and Mg 2+ into calcite under karst-analogue experimental conditions

    Microsoft Academic Search

    Yiming Huang; Ian J Fairchild

    2001-01-01

    There is a paucity of experimental data on calcite precipitation from waters at low ionic strength and low ratios of Mg\\/Ca and Sr\\/Ca, using controlled and constant precipitation rates. Such data are particularly needed for studies of speleothem geochemistry in relation to palaeoclimates.We carried out a series of experiments using a karst-analogue set-up in a chamber of constant temperature and

  20. Quantitative laboratory measurements of biogeochemical processes controlling biogenic calcite carbon sequestration.

    SciTech Connect

    Zendejas, Frank; Lane, Todd W.; Lane, Pamela D.

    2011-01-01

    The purpose of this LDRD was to generate data that could be used to populate and thereby reduce the uncertainty in global carbon cycle models. These efforts were focused on developing a system for determining the dissolution rate of biogenic calcite under oceanic pressure and temperature conditions and on carrying out a digital transcriptomic analysis of gene expression in response to changes in pCO2, and the consequent acidification of the growth medium.

  1. Continuous 500,000-year climate record from vein calcite in Devils Hole, Nevada

    Microsoft Academic Search

    I. J. Winograd; T. B. Coplen; J. M. Landwehr; K. M. Revesz; A. C. Riggs; K. R. Ludwig; B. J. Szabo; P. T. Kolesar

    1992-01-01

    Oxygen-18 (δ¹⁸O) variations in a 36-centimeter-long core (DH-11) of vein calcite from Devils Hole, Nevada, yield an uninterrupted 500,000-year paleotemperature record that closely mimics all major features in the Vostok (Antarctica) paleotemperature and marine δ¹⁸O ice-volume records. The chronology for this continental record is based on 21 replicated mass-spectrometric uranium-series dates. Between the middle and latest Pleistocene, the duration of

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

    E-print Network

    Grosell, Martin

    solubility product constant (pK*sp) is defined as: pKsp ¼ ÀLog Ca2þ Â Ã 1Àxð Þ Mg2þ Â Ãx CO3 2À Â Ã ð2ÞThe solubility of fish-produced high magnesium calcite in seawater Ryan J. Woosley,1 Frank J the first measurements of the solubility of this CaCO3 in seawater. The resulting solubility (pK*sp = 5.89 Æ

  3. On the Direction and Magnitude of Oxygen Isotope Fractionation Between Calcite and Aragonite at Thermodynamic Equilibrium

    Microsoft Academic Search

    Gen-Tao Zhou; Yong-Fei Zheng

    2006-01-01

    Oxygen isotope fractionation factors between calcium carbonates and water have been applied to ancient marine geochemistry\\u000a principally for the purpose of geothermometry. The problem was encountered, however, with respect to the direction and magnitude\\u000a of oxygen isotope fractionation between calcite and aragonite at thermodynamic equilibrium. This basically involves sound\\u000a understanding of both thermodynamics and kinetics of oxygen isotope fractionation between

  4. Assessment of Three Spectroscopic Techniques for Rapid Estimation of Calcite in Copper Ore

    Microsoft Academic Search

    Pedro Escarate Monetta; Andrés R. Guesalaga; Valerio Rossi Albertini; Daniele Bailo

    2010-01-01

    This paper presents the assessment of three spectroscopic techniques, i.e., Raman spectroscopy (RS), ultraviolet fluorescence (UVF) spectroscopy, and energy-dispersive X-ray diffraction (ED-XRD), for measuring calcite (CaCO3) concentration in copper ore. The results for the three methods are compared in terms of their correlation coefficient R2 and prediction error (root-mean-square error of prediction, RMSEP). These approaches substantially shorten the measurement time

  5. Identification of spectrally similar materials using the USGS Tetracorder algorithm: The calcite-epidote-chlorite problem

    USGS Publications Warehouse

    Dalton, J.B.; Bove, D.J.; Mladinich, C.S.; Rockwell, B.W.

    2004-01-01

    A scheme to discriminate and identify materials having overlapping spectral absorption features has been developed and tested based on the U.S. Geological Survey (USGS) Tetracorder system. The scheme has been applied to remotely sensed imaging spectroscopy data acquired by the Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) instrument. This approach was used to identify the minerals calcite, epidote, and chlorite in the upper Animas River watershed, Colorado. The study was motivated by the need to characterize the distribution of calcite in the watershed and assess its acid-neutralizing potential with regard to acidic mine drainage. Identification of these three minerals is difficult because their diagnostic spectral features are all centered at 2.3 ??m, and have similar shapes and widths. Previous studies overestimated calcite abundance as a result of these spectral overlaps. The use of a reference library containing synthetic mixtures of the three minerals in varying proportions was found to simplify the task of identifying these minerals when used in conjunction with a rule-based expert system. Some inaccuracies in the mineral distribution maps remain, however, due to the influence of a fourth spectral component, sericite, which exhibits spectral absorption features at 2.2 and 2.4 ??m that overlap the 2.3-??m absorption features of the other three minerals. Whereas the endmember minerals calcite, epidote, chlorite, and sericite can be identified by the method presented here, discrepancies occur in areas where all four occur together as intimate mixtures. It is expected that future work will be able to reduce these discrepancies by including reference mixtures containing sericite. ?? 2004 Elsevier Inc. All rights reserved.

  6. Microbial calcite, a bio-based smart nanomaterial in concrete remediation

    Microsoft Academic Search

    S. S. Bang; J. J. Lippert; U. Yerra; S. Mulukutla; V. Ramakrishnan

    2010-01-01

    The concept of developing a biosealant in concrete remediation is based on unique microbial metabolic processes. A common soil microorganism, Sporosarcina pasteurii, can induce CaCO3 precipitation in the surroundings in response to environmental cues such as high pH and available nutrients and minerals. A new biomolecule, microbial calcite is introduced as a smart nanomaterial for self-healing concrete – its effects

  7. The Thermal Evolution of the Ouachita Orogen, Arkansas and Oklahoma from Quartz-Calcite Thermometry and Fluid Inclusion Thermobarometry 

    E-print Network

    Piper, Jennifer

    2012-02-14

    To understand the fluid temperature and pressure during the Ouachita orogeny, we used isotopic analysis of syntectonic veins and adjacent host material, quartz-calcite oxygen isotope thermometry and fluid inclusion analysis. The veins were...

  8. Parthenocarpy and Seed Predation by Insects in Bursera morelensis

    PubMed Central

    Ramos-Ordoñez, María F.; Márquez-Guzmán, Judith; Del Coro Arizmendi, Ma.

    2008-01-01

    Background and Aims While parthenocarpy (meaning the production of fruits without seeds) may limit fecundity in many plants, its function is not clear; it has been proposed, however, that it might be associated with a strategy to avoid seed predation. Bursera morelensis is a dioecious endemic plant that produces fruits with and without seeds, and its fruits are parasitized by insects. Its reproductive system is not well described and no published evidence of parthenocarpy exists for the species. The purpose of this work was to describe the breeding system of B. morelensis and its relationship to seed predation by insects. Methods The breeding system was described using pollination experiments, verifying the presence of parthenocarpic fruits and apomictic seeds. Reproductive structures from flower buds to mature fruits were quantified. For fruits, an anatomical and histological characterization was made. The number of fruits in which seeds had been predated by insects was correlated with parthenocarpic fruit production. Key Results The major abortion of reproductive structures occurred during fruit set. The results discard the formation of apomictic seeds. Flowers that were not pollinated formed parthenocarpic fruits and these could be distinguished during early developmental stages. In parthenocarpic fruits in the first stages of development, an unusual spread of internal walls of the ovary occurred invading the locule and preventing ovule development. Unlike fruits with seeds, parthenocarpic fruits do not have calcium oxalate crystals in the ovary wall. Both fruit types can be separated in the field at fruit maturity by the presence of dehiscence, complete in seeded and partial in parthenocarpic fruits. Trees with more parthenocarpic fruits had more parasitized fruits. Conclusions This is the first time the anatomy of parthenocarpic fruits in Burseraceae has been described. Parthenocarpic fruits in B. morelensis might function as a deceit strategy for insect seed predators as they are unprotected both chemically and mechanically by the absence of calcium oxalate crystals. PMID:18755701

  9. Fulvic acid like organic compounds control nucleation of marine calcite under suboxic conditions

    NASA Astrophysics Data System (ADS)

    Neuweiler, Fritz; D'Orazio, Valeria; Immenhauser, Adrian; Geipel, Gerhard; Heise, Karl-Heinz; Cocozza, Claudio; Miano, Teodoro M.

    2003-08-01

    Intracrystalline organic compounds, enclosed within in situ precipitated marine microcrystalline calcite (automicrite), might represent either an inclusion or the catalyst of such precipitation. We use evidence from a Lower Cretaceous deep-water carbonate mound to show (1) the original source, (2) the degree of condensation, (3) the redox conditions involved, and (4) the catalytic role of natural organic matter for the precipitation of automicrite. Fluorescence spectrometry of the intracrystalline organic fraction extracted from these carbonates identifies a marine fulvic acid like organic compound with a low degree of polycondensation. This finding points to a temporal correlation of the initial stage of geopolymer formation with the precipitation of automicrite. Furthermore, the rare earth element (REE) distribution patterns in the mineral show a consistent positive Ce anomaly, suggesting an episode of reductive dissolution of iron-manganese oxyhydroxides during automicrite formation. In general, a relative enrichment of middle-weight REEs is observed, resulting in a convex distribution pattern typical for, e.g., phosphate concretions or humic acid material. By merging the results of spectrometry and REE geochemistry we thus conclude that the marine calcite precipitation was catalyzed by marine fulvic acid like compounds during the early stages of humification under suboxic conditions. This indicates that humification, driven by the presence of a benthic biomass, is more important for calcite authigenesis than any site-specific microbial metabolism. The Neoproterozoic rise of carbonate mounds supports this hypothesis; there is molecular evidence for early metazoan divergence then, but not for a major evolutionary episode of microorganisms.

  10. Calcite production by Coccolithophores in the South East Pacific Ocean: from desert to jungle

    NASA Astrophysics Data System (ADS)

    Beaufort, L.; Couapel, M.; Buchet, N.; Claustre, H.

    2007-09-01

    BIOSOPE cruise achieved an oceanographic transect from the Marquise Islands to the Peru-Chili upwelling (PCU) via the centre of the South Pacific Gyre (SPG). Water samples from 6 depths in the euphotic zone were collected at 20 stations. The concentrations of suspended calcite particles, coccolithophores cells and detached coccoliths were estimated together with size and weight using an automatic polarizing microscope, a digital camera, and a collection of softwares performing morphometry and pattern recognition. Some of these softwares are new and described here for the first time. The coccolithophores standing stocks are usually low and reach maxima west of the PCU. The coccoliths of Emiliania huxleyi, Gephyrocapsa spp. and Crenalithus spp. (Order Isochrysidales) represent 50% of all the suspended calcite particles detected in the size range 0.1-46 ?m (21% of PIC in term of the calcite weight). The latter species are found to grow preferentially in the Chlorophyll maximum zone. In the SPG their maximum concentrations was found to occur between 150 and 200 m, which is very deep for these taxa. The weight and size of coccoliths and coccospheres are correlated. Large and heavy coccoliths and coccospheres are found in the regions with relative higher fertility in the Marquises Island and in the PCU. Small and light coccoliths and coccospheres are found west of the PCU. This distribution may correspond to that of the concentration of calcium and carbonate ions.

  11. A field and modeling study of fractured rock permeability reduction using microbially induced calcite precipitation.

    PubMed

    Cuthbert, Mark O; McMillan, Lindsay A; Handley-Sidhu, Stephanie; Riley, Michael S; Tobler, Dominique J; Phoenix, Vernon R

    2013-12-01

    Microbially induced calcite precipitation (MICP) offers an attractive alternative to traditional grouting technologies for creating barriers to groundwater flow and containing subsurface contamination, but has only thus far been successfully demonstrated at the laboratory scale and predominantly in porous media. We present results of the first field experiments applying MICP to reduce fractured rock permeability in the subsurface. Initially, the ureolytic bacterium, Sporosarcina pasteurii, was fixed in the fractured rock. Subsequent injection of cementing fluid comprising calcium chloride and urea resulted in precipitation of large quantities (approximately 750 g) of calcite; significant reduction in the transmissivity of a single fracture over an area of several m(2) was achieved in around 17 h of treatment. A novel numerical model is also presented which simulates the field data well by coupling flow and bacterial and solute reactive transport processes including feedback due to aperture reduction via calcite precipitation. The results show that MICP can be successfully manipulated under field conditions to reduce the permeability of fractured rock and suggest that an MICP-based technique, informed by numerical models, may form the basis of viable solutions to aid pollution mitigation. PMID:24147737

  12. Grain boundaries as microreactors during reactive fluid flow: experimental dolomitization of a calcite marble

    NASA Astrophysics Data System (ADS)

    Etschmann, B.; Brugger, J.; Pearce, M. A.; Ta, C.; Brautigan, D.; Jung, M.; Pring, A.

    2014-08-01

    Limestone dolomitization is an example of a fluid-induced mineralogical transformation that commonly affects extensive rock volumes. To understand the mechanisms enabling these efficient replacement reactions, we investigated experimentally the dolomitization of a fractured calcite marble under flow-through conditions at mild hydrothermal conditions. Contrary to most earlier studies of coupled dissolution reprecipitation reactions that were conducted using small, individual grains, in this study, the integrity of the rock was preserved, so that the experiment explored the links between flow in a fracture and fluid-rock interaction. In these experiments, grain boundaries acted as microreactors, in which a Mg-poor `protodolomite' formed initially, and then transformed into dolomite. The difficulty in nucleating dolomite played a key role in controlling the evolution of the porosity, by allowing for (1) initial dissolution along grain boundaries, and (2) formation of coarse porosity at the reaction interface. This porosity evolution not only enabled the reaction to progress efficiently, but also controlled the mineralogy of the system, as shown by brucite replacing calcite near the fracture once the fluid along calcite grain boundaries became sufficiently connected to the fluid flowing through the fracture. This study illustrates the role of grain boundaries, porosity evolution and nucleation in controlling reaction progress as well as the nature and textures of the products in pervasive mineralogical transformations.

  13. Transient calcite fracture fillings in a welded tuff, Snowshoe Mountain, Colorado

    USGS Publications Warehouse

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

    2000-01-01

    The core from two boreholes (13.1 and 19.2 m depth) drilled 500 m apart in the fractured, welded tuff near the summit of the Snowshoe Mountain, Colorado (47??30'N, 106??55'W) had unique petrographic and hydrodynamic properties. Borehole SM-4 had highly variable annual water levels, in contrast to SM-1a, whose water level remained near the land surface. Core samples from both boreholes (n = 10 and 11) were examined petrographically in thin sections impregnated with epoxy containing rhodamine to mark the pore system features, and were analyzed for matrix porosity and permeability. Core from the borehole sampling the vadose zone was characterized by open fractures with enhanced porosity around phenocrysts due to chemical weathering. Fractures within the borehole sampling the phreatic zone were mineralized with calcite and had porosity characteristics similar to Unweathered and unfractured rock. At the top of the phreatic zone petrography indicates that calcite is dissolving, thereby changing the hydrogeochemical character of the rock (i.e. permeability, porosity, reactive surface area, and mineralogy). Radiocarbon ages and C and O stable isotopes indicate that calcite mineralization occurred about 30 to 40 ka ago and that there was more than one mineralization event. Results of this study also provide some relationships between primary porosity development from 3 types of fracture in a welded tuff. (C) 2000 Elsevier Science Ltd.

  14. Viruses Occur Incorporated in Biogenic High-Mg Calcite from Hypersaline Microbial Mats

    PubMed Central

    De Wit, Rutger; Gautret, Pascale; Bettarel, Yvan; Roques, Cécile; Marlière, Christian; Ramonda, Michel; Nguyen Thanh, Thuy; Tran Quang, Huy; Bouvier, Thierry

    2015-01-01

    Using three different microscopy techniques (epifluorescence, electronic and atomic force microscopy), we showed that high-Mg calcite grains in calcifying microbial mats from the hypersaline lake “La Salada de Chiprana”, Spain, contain viruses with a diameter of 50–80 nm. Energy-dispersive X-ray spectrometer analysis revealed that they contain nitrogen and phosphorus in a molar ratio of ~9, which is typical for viruses. Nucleic acid staining revealed that they contain DNA or RNA. As characteristic for hypersaline environments, the concentrations of free and attached viruses were high (>1010 viruses per g of mat). In addition, we showed that acid treatment (dissolution of calcite) resulted in release of viruses into suspension and estimated that there were ~15 × 109 viruses per g of calcite. We suggest that virus-mineral interactions are one of the possible ways for the formation of nano-sized structures often described as “nanobacteria” and that viruses may play a role in initiating calcification. PMID:26115121

  15. Effect of calcite on Pb-doped solidified waste forms in leaching.

    PubMed

    Lee, Dong-Jin

    2006-06-01

    The alkalinity of cementitious materials rectifies a low pH of leachant to be over 12 in leaching. The rapid change of leachant pH produces the remarked variation of solubility of heavy metals in the toxicity characteristic leaching procedure. The release of lead on cementitious solid waste forms in leaching was observed in the pH range of particularly 12. The release of lead is significant dependant on the changed values of leachant pH. The pH static leaching procedure (PSLP) was implemented for assessing a quantitative measurement of total potential leachability with the continuing addition of acidic leachant up to the point of no change of leachant pH. The release of lead on Pb-doped solidified waste forms (SWF), in the PSLP, was 27.0% of initial concentration at the maximum meq CH3COOH (about 24.0) added to g dry solidified wastes. In this study, the immobilization effect of calcite on SWF was investigated in the acidic condition by the PSLP. Calcite additions to SWF make a good fixation efficiency of about 92%. Calcite addition abundantly provides the acid neutralization capacity to protect SWF from the attack of acid, with the marked development of hydrated minerals (mainly portlandite and C-S-H) in accordance with the accelerating effect of cement hydration. PMID:16376409

  16. The transformation of vaterite to calcite: effect of the conditions of the solutions in contact with the mineral phase

    Microsoft Academic Search

    Nikos Spanos; Petros G. Koutsoukos

    1998-01-01

    The transformation of the thermodynamically unstable vaterite into the stable calcite was investigated during the precipitation of calcium carbonate, under conditions of constant supersaturation at 25, 35 and 45°C and pHs 8.5, 9.0 and 10.0. The calcite content in the solid precipitates was determined quantitatively by the X-ray diffraction technique (XRD) using the appropriate mixed standards of known composition. Scanning

  17. Calibration of stable isotope composition of Thoracosphaera heimii (dinoflagellate) calcite for reconstructing paleotemperatures in the intermediate photic zone

    NASA Astrophysics Data System (ADS)

    Minoletti, Fabrice; Hermoso, Michaël.; Candelier, Yaël.; Probert, Ian

    2014-12-01

    In this study we investigate the temperature dependence of oxygen isotope ratios preserved in calcite formed by the dinoflagellate Thoracosphaera heimii, focusing primarily on the development of a geological proxy. Geochemical analysis of the calcite shells produced by this species represents a valuable proxy for reconstructing environmental conditions in the intermediate photic zone. Calibration is based on isotopic analysis from culture experiments performed in very dilute batch conditions, as well as from near-monospecific T. heimii assemblages separated from core top sediments. Results are similar for both approaches and indicate that T. heimii shells have oxygen isotope compositions close to equilibrium values predicted for inorganic calcite precipitation. This calibration of the isotopic composition of dinoflagellate calcite indicates that monospecific assemblages of T. heimii can be used to unravel paleotemperatures in the intermediate photic zone by applying isotopic transfer functions for equilibrium calcite. In culture, however, a ?18O offset of -1‰ is observed at temperatures <17°C, which falls below the natural temperature range of this species. Culture analyses also reveal a relationship between temperature and carbon isotope composition of calcite. The mechanisms behind this relationship remain to be explored, but their identification may provide a better understanding of carbon isotope systematics from both biogeochemical and geological perspectives. Comparison of the oxygen isotope composition of T. heimii shells with that of shallower dwelling organisms, such as the coccolithophores, represents a valuable proxy for determining temperature gradients within the photic zone and may enable reconstruction of the evolution of the depth of the thermocline.

  18. Oxygen isotope exchange processes and disequilibrium between calcite and forsterite in an experimental C-O-H fluid

    SciTech Connect

    Zheng, Y.F. [Univ. of Science and Technology of China, Hefei (China). Dept. of Earth and Space Sciences] [Univ. of Science and Technology of China, Hefei (China). Dept. of Earth and Space Sciences; [Univ. of Tuebingen (Germany). Inst. for Mineralogy, Petrology and Geochemistry; Satir, M.; Metz, P. [Univ. of Tuebingen (Germany). Inst. for Mineralogy, Petrology and Geochemistry] [Univ. of Tuebingen (Germany). Inst. for Mineralogy, Petrology and Geochemistry; Sharp, Z.D. [Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Earth and Planetary Sciences] [Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Earth and Planetary Sciences

    1999-06-01

    Oxygen isotope exchange between calcite and forsterite were investigated in the presence of a large amount of supercritical fluid. The experiments were conducted in standard cold-seal pressure vessels at 680 C and 500 MPa in the T-P-X{sub CO{sub 2}} stability field of the calcite-forsterite assemblage for 2, 5, 10, 20, 40 and 80 days, respectively. The weight ratio of mineral to fluid in the starting mixture is 1.46; the fluid was a mixture of H{sub 2}O and CO{sub 2} with the mole fraction of CO{sub 2} being 0.1. The results show that the oxygen isotope exchange between the minerals was accomplished via mineral-fluid exchange by a dual-mechanism, i.e. initial rapid exchange due to Ostwald ripening of both calcite and forsterite, followed by a slower diffusion-controlled process. Furthermore, for the given fluid composition, calcite shows a greater rate of dissolution-recrystallization and oxygen isotope exchange with fluid than forsterite. As a result, oxygen isotope fractionations between calcite and forsterite and between the minerals and the fluid can simply pass the equilibrium fractionations with time and even lead to crossover behavior. Once diffusion becomes a primary mechanism for further isotope exchange in the three-phase system, the rate of oxygen diffusion in calcite is equal to, or slightly less than that in forsterite.

  19. Crystals of cadmium, zinc metallothionein.

    PubMed Central

    Melis, K A; Carter, D C; Stout, C D; Winge, D R

    1984-01-01

    Single crystals have been grown of Cd,Zn metallothionein isoform II from rat liver. The space group is P41212(P43212) with unit cell dimensions a = b = 31.0 A and c = 120.0 A, and one molecule in the crystallographic asymmetric unit. The crystals are square bipyramids elongated on the tetragonal c-axis and are grown by repetitive seeding. The crystals are suitable for high resolution structure analysis. Assays of dissolved crystals show that the crystals have the same Cd and Zn content and amino acid composition as the native, as-isolated protein. Images FIGURE 1. FIGURE 2. (a) FIGURE 2. (b) FIGURE 4. FIGURE 5. PMID:6734549

  20. Crystal agglomeration is a major element in calcium oxalate urinary stone formation

    Microsoft Academic Search

    Dik J Kok; Socrates E Papapoulos; Olav L M Bijvoet

    1990-01-01

    Crystal agglomeration is a major element in calcium oxalate urinary stone formation. The effects of urines from 36 healthy subjects and 86 calcium oxalate renal stone formers on calcium oxalate monohydrate crystallization kinetics were studied using a seeded crystal growth method in which the solubility, the growth and the agglomeration of the crystals are measured as three separate and system-independent

  1. Snow Crystals

    NSDL National Science Digital Library

    Kenneth Libbrecht

    1999-02-01

    This site is all about snow crystals and snowflakes. The many facets of snow crystals are described here, along with attempts to understand their formation. This site includes collections of super-high-resolution snow crystal photos, as well as links to learn about snow crystal classifications and how to make snow crystal fossils. Included in the study of how snow crystals form, these researchers have created snow crystals in the laboratory. Their snow crystal galleries include selections of images and movies of laboratory-grown snow crystals, as well as information on how to make your own snow crystals. The snow crystal primer describes what snow crystals are, how they form, and why they form the way they do. There is also a section on snow crystal physics.

  2. Crystal Structure of the Bowman-Birk Inhibitor from Vigna unguiculata Seeds in Complex with ?-Trypsin at 1.55 Å Resolution and Its Structural Properties in Association with Proteinases

    Microsoft Academic Search

    João Alexandre R. G. Barbosa; Luciano P. Silva; Rozeni C. L. Teles; Gisele F. Esteves; Ricardo B. Azevedo; Manuel M. Ventura; Sonia M. de Freitas

    2007-01-01

    The structure of the Bowman-Birk inhibitor from Vigna unguiculata seeds (BTCI) in complex with ?-trypsin was solved and refined at 1.55Å to a crystallographic Rfactor of 0.154 and Rfree of 0.169, and represents the highest resolution for a Bowman-Birk inhibitor structure to date. The BTCI-trypsin interface is stabilized by hydrophobic contacts and hydrogen bonds, involving two waters and a polyethylene

  3. Seeded growth of TPA-MFI films using the fluoride route

    Microsoft Academic Search

    Magdalena Lassinantti Gualtieri; Alessandro F. Gualtieri; Maria Prudenziati

    2008-01-01

    The fluoride route in combination with surface seeding was used for the preparation of TPA-MFI films on dense amorphous silica glass supports. The use of F? as mineralizing agent allowed the crystallization of TPA-MFI at near-neutral pH (6.7±0.1). The supports were seeded with colloidal TPA-MFI crystals and hydrothermally treated in a synthesis gel at 100°C for various durations (24–192h). The

  4. 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)

  5. The Enhanced Geothermal System of Soultz-sous-Forêts: A study of the relationships between fracture zones and calcite content

    NASA Astrophysics Data System (ADS)

    Hébert, Ronan L.; Ledésert, Béatrice; Bartier, Danièle; Dezayes, Chrystel; Genter, Albert; Grall, Céline

    2010-09-01

    The Enhanced Geothermal System (EGS) of Soultz-sous-Forêts (France) is made of three boreholes (GPK2, GPK3 and GPK4). The hydraulic connection between the wells, which is crucial to get an efficient geothermal exchanger, may be unfortunately hindered by the more or less complete sealing of fractures by hydrothermal neoformed minerals. This paper takes over the recent work of the authors that quantified the amounts of calcite on a random sampling within the three boreholes in order to assess the role of this mineral on the exchanger zone and in particular its influence on the permeability of the flow pathways. In the present study we focused the sampling on the fracture zones that have been identified as flow pathways. Now, all the three wells show high (above 10 wt.%) and moderate to low (between 2.0 and 7.0 wt.%) calcite anomalies. In GPK2, fracture zones with a high conductivity are characterized by high calcite content, and those with a low conductivity by low calcite content. The fracture zones of GPK3 show the opposite relationship: the most efficient flow pathways have a low calcite content, whilst the less conductive show a high calcite content. Fluid flow in GPK4 is mainly accommodated by the fracture zone at 4775 m MD that is not calcite rich. The other fracture zones of GPK4, which are interpreted with a similar and low conductivity, show low, moderate and high calcite contents. These data show clearly that GPK2 is different from GPK3 and GPK4, these two later being more comparable. It suggests that the fracture zones themselves may be of different type, and that the connectivity to the fracture network may be different too. This difference of behaviour is consistent with microseismicity data showing that GPK2 is characterized by a rather compact and well structured network of medium-scale fracture whereas GPK3 and GPK4 are altogether characterized by more localized and discrete fracture zones. Some issues remain such as the occurrence of calcite anomalies with no evident relationship with fracture zones, as well as the occurrence of identified flow pathways with no abnormal calcite content.

  6. Perlinhibin, a cysteine-, histidine-, and arginine-rich miniprotein from abalone (Haliotis laevigata) nacre, inhibits in vitro calcium carbonate crystallization.

    PubMed

    Mann, Karlheinz; Siedler, Frank; Treccani, Laura; Heinemann, Fabian; Fritz, Monika

    2007-08-15

    We have isolated a 4.785 Da protein from the nacreous layer of the sea snail Haliotis laevigata (greenlip abalone) shell after demineralization with acetic acid. The sequence of 41 amino acids was determined by Edman degradation supported by mass spectrometry. The most abundant amino acids were cysteine (19.5%), histidine (17%), and arginine (14.6%). The positively charged amino acids were almost counterbalanced by negatively charged ones resulting in a calculated isoelectric point of 7.86. Atomic-force microscopy studies of the interaction of the protein with calcite surfaces in supersaturated calcium carbonate solution or calcium chloride solution showed that the protein bound specifically to calcite steps, inhibiting further crystal growth at these sites in carbonate solution and preventing crystal dissolution when carbonate was substituted with chloride. Therefore this protein was named perlinhibin. X-ray diffraction investigation of the crystal after atomic-force microscopy growth experiments showed that the formation of aragonite was induced on the calcite substrate around holes caused by perlinhibin crystal-growth inhibition. The strong interaction of the protein with calcium carbonate was also shown by vapor diffusion crystallization. In the presence of the protein, the crystal surfaces were covered with holes due to protein binding and local inhibition of crystal growth. In addition to perlinhibin, we isolated and sequenced a perlinhibin-related protein, indicating that perlinhibin may be a member of a family of closely related proteins. PMID:17496038

  7. Crystal Creations.

    ERIC Educational Resources Information Center

    Whipple, Nona; Whitmore, Sherry

    1989-01-01

    Presents a many-faceted learning approach to the study of crystals. Provides instructions for performing activities including crystal growth and patterns, creating miniature simulations of crystal-containing rock formations, charcoal and sponge gardens, and snowflakes. (RT)

  8. Cloud Seeding What is it.... "It is a science that can be used to control winds, suppress hail, dissolve fog or create

    E-print Network

    Toohey, Darin W.

    Cloud Seeding What is it.... "It is a science that can be used to control winds, suppress hail, dissolve fog or create rain."...."assisting nature"...."Cloud seeding essentially helps that process along for seeding. It most resembles an ice crystal when it freezes and thus is the best option to start a cloud

  9. Research support for cadmium telluride crystal growth

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz

    1995-01-01

    The growth of single crystals of zinc selenide was carried out by both closed ampoule physical vapor transport and effusive ampoule physical vapor transport (EAPVT). The latter technique was shown to be a much more efficient method for the seeded growth of zinc selenide, resulting in higher transport rates. Furthermore, EAPVT work on CdTe has shown that growth onto (n 11) seeds is advantageous for obtaining reduced twinning and defect densities in II-VI sphalerite materials.

  10. Planting Seeds of Involvement

    ERIC Educational Resources Information Center

    Allyn, David

    2004-01-01

    In New Jersey, bright elementary and middle school students whose parents are financially limited have an opportunity to participate in a program called New Jersey SEEDS (Scholars, Educators, Excellence, Dedication, Success). SEEDS provides intellectually challenging academic enrichment classes on Saturdays and during the summer so that students…

  11. Needs of Seeds

    NSDL National Science Digital Library

    Francis Eberle

    2007-01-01

    The purpose of this assessment probe is to elicit students' ideas about seeds. It specifically probes to find out if students recognize that a seed has needs, similar to other organisms that allow it to develop into the next stage of its life cycle.

  12. Imprinting and Seed Development

    Microsoft Academic Search

    Mary Gehring; Yeonhee Choi; Robert L. Fischer

    2004-01-01

    Fertilization Seeds consist of three genetically distinct components: embryo, endosperm, and seed coat. In plants, mitosis follows meiosis to produce the haploid phase of the plant life cycle, the male and female gametophytes. The angiosperm female gametophyte, the site of fertilization, is completely embedded within the maternal sporophytic tissues of the ovule. The most prevalent type of mature female gametophyte

  13. Planning cloud seeding research

    Microsoft Academic Search

    F. H. Ludlam

    1955-01-01

    It is suggested that a theory of cloud seeding needs to be developed before seeding experiments can be properly planned and assessed. This theory will arise from improved knowledge of cloud processes gained by the study of natural clouds. Some techniques used in observing shower clouds in Sweden are described, and some preliminary results mentioned.

  14. Ant–seed mutualisms

    Microsoft Academic Search

    Jennifer A Zettler; Timothy P Spira; Craig R Allen

    2001-01-01

    Invasion by the red imported fire ant, Solenopsis invicta, has had negative impacts on individual animal and plant species, but little is known about how S. invicta affects complex mutualistic relationships. In some eastern forests of North America, 30% of herbaceous species have ant-dispersed seeds. We conducted experiments to determine if fire ants are attracted to seeds of these plant

  15. The Seed Ecology of

    Microsoft Academic Search

    Richy J. Harrodl; Charles B. Halpern

    2005-01-01

    We examined the seed ecology of Iliamna longisepala as an aid to developing a conserva- tion strategy for this rare endemic forb of northcentral Washington. We conducted field, greenhouse, and laboratory studies to quantify: (1) densities of buried viable seed among sites with different histories of burning, (2) post-fire spatial distributions of germinants relative to reproductive plants and bum se-

  16. When Seed Dispersal Matters

    NSDL National Science Digital Library

    HENRY F. HOWE and MARIA N. MIRITI (; )

    2004-07-01

    This peer-reviewed resource from Bioscience journal is about the varying importance of seed dispersal within plant communities. A profusion of fruit forms implies that seed dispersal plays a central role in plant ecology, yet the chance that an individual seed will ultimately produce a reproductive adult is low to infinitesimal. Extremely high variance in survival implies that variations in fruit production or transitions from seed to seedling will contribute little to population growth. The key issue is that variance in survival of plant life-history stages, and therefore the importance of dispersal, differs greatly among and within plant communities. In stable communities of a few species of long-lived plants, variances in seed and seedling survival are immense, so seed-to-seedling transitions have little influence on overall population dynamics. However, when seedlings in different circumstances have very different chances of survival--in ecological succession, for example, or when dispersed seeds escape density-dependent mortality near parent trees--the biased survival of dispersed seeds or seedlings in some places rather than others results in pervasive demographic impacts.

  17. The Thermoanalysis of Metal Single Crystals and a New Thermoelectric Effect of Bismuth Crystals Grown in Magnetic Fields

    Microsoft Academic Search

    Alexander Goetz; Maurice F. Hasler

    1930-01-01

    Part I. The Thermoanalysis of Bi Single Crystals Production of crystals.-Crystals of Bi of any desired orientation were grown by the method of Goetz, one half of each normally, the other half within a transversal magnetic field. The orientations, predetermined by a seed crystal, were not affected by this process. Two methods of growth-the continuous and the discontinuous-were used. The

  18. Polyelectrolyte-directed nanoparticle aggregation: systematic morphogenesis of calcium carbonate by nonclassical crystallization.

    PubMed

    Song, Rui-Qi; Cölfen, Helmut; Xu, An-Wu; Hartmann, Jürgen; Antonietti, Markus

    2009-07-28

    Besides the classical atom/ion/molecule based mechanism, nonclassical crystallization provides a nanoparticle-based crystallization pathway toward single crystals. However, there is a lack of experimentally established strategies for engineering a range of crystalline microstructures from common nanoparticles by nonclassical crystallization. We demonstrate that a commercial random copolymer polyelectrolyte poly(4-styrene sulfonate)-co-(maleic acid) (PSS-co-MA) considerably guides crystallization of calcium carbonate (CC) with a high versatility. The bioinspired nonclassical crystallization protocol yielded a series of calcite microstructures. Calcite single crystals obtained at low supersaturation show a pseudo-dodecahedral shape with curved faces, whereas increasing supersaturation generated calcite mesocrystals with pseudo-octahedral shapes and scalloped surfaces. Further increase of supersaturation induced the formation of polycrystalline multilayered and hollow spheres. In the initial growth stage of all these microstructures, amorphous CC nanoparticles formed as the early product. Remarkably, microparticles with minimal primitive (P)-surface were captured as the prominent intermediate indicative of liquidlike behavior. Moreover, nanogranular structures exist broadly in the as-synthesized crystals. These results demonstrate that the polyelectrolyte can effectively stabilize the amorphous CC nanoparticle precursors, impart control over the evolution from amorphous precursors via a liquid aggregate through P-surface intermediates to the final crystals, and thus allow the morphogenesis. Simple variation of calcium and polyeletrolyte concentrations enables a systematic control over the size and morphology of particles among pseudo-dodecahedra, pseudo-octahedra, multilayered spheres, and hollow spheres, which are expressed in a morphology diagram. A unifying nanoparticle aggregation formation mechanism was suggested to explain the morphogenesis by the combination of nonclassical crystallization and surface area minimization principles. PMID:19572617

  19. Crystallization in solid solution-aqueous solution systems: Thermodynamic and kinetic approaches

    SciTech Connect

    Shtukenberg, A. G., E-mail: shtukenberg@mail.ru; Punin, Yu. O. [St. Petersburg State University (Russian Federation); Azimov, P. Ya. [Institute of Precambrian Geology and Geochronology (Russian Federation)

    2010-03-15

    A new phenomenological approach is proposed to describe the crystallization kinetics in solid solution-aqueous solution binary systems. The phase diagrams, equilibria, and quasie-quilibria are considered within this approach. The crystallization kinetics near the true equilibrium and the crystallization features at large deviations from equilibrium are discussed on this basis. Special attention is paid to possible interactions in a solution with a seed crystal placed in it. In particular, the interactions leading to the seed's crystal growth or dissolution and to a possible exchange or metasomatic reactions are considered. In addition, the effect of the generated mismatch stress on the crystal growth rate and composition is analyzed.

  20. Characterization of calcium carbonate crystals in pigeon yolk sacs with different incubation times.

    PubMed

    Song, Juan; Cheng, Haixia; Shen, Xinyu; Hu, Jingxiao; Tong, Hua

    2014-05-01

    Calcium carbonate crystals are known to form in the yolk sacs of fertile pigeon eggs at late stages of incubation. The composition and structure of these crystals were investigated, the crystallization environment was inspected, and the physical chemistry constants of the yolk fluid were determined through the incubation period. Polarized light microscopy was used to observe the generation and distribution of calcium carbonate crystals in the yolk sac. In addition, X-ray diffraction was employed to analyze the composition and crystal phase of the yolk sac. A decalcification and deproteination method was established to analyze the ultrastructure and composition of the crystals, as well as the internal relationship between inorganic and organic phases of the crystals. Additionally, scanning electron microscopy, transmission electron microscopy, X-ray energy dispersive spectroscopy, and Fourier transform infrared spectroscopy were used to evaluate the characteristics of the crystals. Our results demonstrated that the calcium carbonate crystals were mainly composed of vaterite and calcite, with vaterite being the major component. Vaterite, a type of biomaterial generated by an organic template control, presented as a concentric hierarchical spherical structure. The organic nature of the biomaterial prevented vaterite from transforming into calcite, which is more thermodynamically stable than vaterite. Additionally, the configuration, size, and aggregation of vaterite were also mediated by the organic template. This bio-vaterite was found during the incubation period and is valuable in calcium transport during embryonic development. PMID:24602270

  1. 7 CFR 201.15 - Weed seeds.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 3 2011-01-01 2011-01-01 false Weed seeds. 201.15 Section 201.15 Agriculture...REGULATIONS Labeling Agricultural Seeds § 201.15 Weed seeds. The percentage of weed seeds shall include seeds of plants...

  2. 7 CFR 201.15 - Weed seeds.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 3 2013-01-01 2013-01-01 false Weed seeds. 201.15 Section 201.15 Agriculture...REGULATIONS Labeling Agricultural Seeds § 201.15 Weed seeds. The percentage of weed seeds shall include seeds of plants...

  3. 7 CFR 201.15 - Weed seeds.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 3 2010-01-01 2010-01-01 false Weed seeds. 201.15 Section 201.15 Agriculture...REGULATIONS Labeling Agricultural Seeds § 201.15 Weed seeds. The percentage of weed seeds shall include seeds of plants...

  4. 7 CFR 201.15 - Weed seeds.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 3 2012-01-01 2012-01-01 false Weed seeds. 201.15 Section 201.15 Agriculture...REGULATIONS Labeling Agricultural Seeds § 201.15 Weed seeds. The percentage of weed seeds shall include seeds of plants...

  5. 7 CFR 201.15 - Weed seeds.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 3 2014-01-01 2014-01-01 false Weed seeds. 201.15 Section 201.15 Agriculture...REGULATIONS Labeling Agricultural Seeds § 201.15 Weed seeds. The percentage of weed seeds shall include seeds of plants...

  6. Magnetic stimulation of marigold seed

    NASA Astrophysics Data System (ADS)

    Afzal, I.; Mukhtar, K.; Qasim, M.; Basra, S. M. A.; Shahid, M.; Haq, Z.

    2012-10-01

    The effects of magnetic field treatments of French marigold seeds on germination, early seedling growth and biochemical changes of seedlings were studied under controlled conditions. For this purpose, seeds were exposed to five different magnetic seed treatments for 3 min each. Most of seed treatments resulted in improved germination speed and spread, root and shoot length, seed soluble sugars and a-amylase activity. Magnetic seed treatment with 100 mT maximally improved germination, seedling vigour and starch metabolism as compared to control and other seed treatments. In emergence experiment, higher emergence percentage (4-fold), emergence index (5-fold) and vigorous seedling growth were obtained in seeds treated with 100 mT. Overall, the enhancement of marigold seeds by magnetic seed treatment with 100 mT could be related to enhanced starch metabolism. The results suggest that magnetic field treatments of French marigold seeds have the potential to enhance germination, early growth and biochemical parameters of seedlings.

  7. Seed Structure and Localization of Reserves in Chenopodium quinoa

    Microsoft Academic Search

    IMELDA PREGO; SARA MALDONADO; MARISA OTEGUI

    1998-01-01

    The three areas of food reserves in quinoa seeds are: a large central perisperm, a peripheral embryo and a one to two-cell layered endosperm surrounding the hypocotyl-radicle axis of the embryo. Cytochemical and ultrastructural analysis revealed that starch grains occupy the cells of the perisperm, while lipid bodies, protein bodies with globoid crystals of phytin, and proplastids with deposits of

  8. Oxygen-isotope composition of diagenetic calcite in organic-rich rocks: Evidence for 18O depletion in marine anaerobic pore water

    Microsoft Academic Search

    Eytan Sass; Amos Bein; Ahuva Almogi-Labin

    1991-01-01

    Upper Cretaceous organic-rich carbonates in Israel contain benthonic foraminifera and varying amounts of early diagenetic infilling of sparry calcite. The sparry calcite has oxygen-isotope values (down to -9.50\\/00 PDB) that are significantly lower than those of the coexisting skeletal calcite (averaging -20\\/00 PDB). Low delta18O values are very common in carbonates that are associated with organic matter. These occurrences are

  9. Testing Novel pH Proxies through Inorganic Calcite Precipitations and K/Pg Foraminifera

    NASA Astrophysics Data System (ADS)

    Super, J. R.; Pagani, M.; Wang, Z.

    2013-12-01

    Ocean pH proxies help constrain the carbon system in the paleocean and can be used to infer atmospheric CO2 when coupled with estimates of total alkalinity, aqueous pCO2 or dissolved inorganic carbon. This project investigates two novel pH proxies (cerium abundance and kinetically-controlled oxygen isotopes) through a series of precipitations of inorganic calcite, as well as the previously established boron isotope pH proxy. Precipitations are performed using varied pH and carbonate saturation states that span the range of typical ocean values as well as a 'free drift' that allows pH and saturation state to vary. The light rare earth element cerium speciates, depending on local oxidation-reduction conditions, between the soluble Ce3+ and highly insoluble Ce4+ ions, causing a relative depletion of cerium in ocean water. This project demonstrates how a suite rare earth elements, including cerium, partitions into inorganic calcite and how partitioning varies with changing pH and carbonate saturation state. Oxygen isotope fractionation is primarily controlled by temperature, but this project examines how pH and carbonate saturation state correlate with oxygen isotope values under kinetic conditions during the initial stage of precipitation. The effect of diagenesis on each proxy is simulated by dissolution of precipitated calcite in a pressure vessel. Results from the precipitations are used to inform a record of well-preserved benthic and planktonic foraminifera from DSDP Site 356 that range in age from the K/Pg boundary to the period when the ?13C gradient between the surface and deep ocean returned to pre-event levels. The pH record is used to infer the magnitude and length of the perturbation to the oceanic carbon system following the extinction event, particularly in terms of export productivity.

  10. Mesozoic oceans: life and evolution in both an aragonitic and calcitic world

    NASA Astrophysics Data System (ADS)

    Hart, Malcolm

    2013-04-01

    The aragonitic ocean of the present day is not typical of a significant part of the Mesozoic, during which there was a calcitic ocean (sensu Stanley, 2006 and Stanley & Hardie, 1998). In the Triassic and early to mid-Jurassic the 'Aragonite ll' ocean was the setting for the origin of many organisms with aragonitic shells, structures and tests (e.g., scleractinian corals, planktic foraminifera), with many of these surviving into the calcitic ocean of the late Jurassic and Cretaceous. In the mid-Late Cretaceous high pCO2 world it is suggested that elevated carbonate saturation levels allowed - for example - benthic communities to both survive and evolve. The Gulf of California has a number of CO2 and CH4 gas 'flares' along faults and fractures in areas such as the Wagner Basin which reduce the seawater (in places) to pH 7.4 or 7.5, potentially approaching Cretaceous conditions, but where benthic foraminifera and other macrofauna appear to survive. The changes in biota during the aragonitic ocean to calcitic ocean transition (and back again) are presented in terms of key features of the evolution of both macrofauna and microfossils (e.g., planktic foraminifera). At many key boundaries (e.g., Triassic/Jurassic and Cretaceous/Paleocene) ocean acidification is being invoked as a medium for biotic change but, in an ocean system somewhat different from the present day, how can this mechanism be assessed and can the acidification of the water column in the oceans and shelf seas occur as rapidly as sometimes postulated?

  11. Establishing a Baseline for Influence of Salinity on Mg Contents in Calcite

    NASA Astrophysics Data System (ADS)

    Stephenson, A. E.; Hunter, J.; Han, N.; Dove, P.

    2008-12-01

    Over the last 20 years, salinity was assumed to have little impact on elemental signatures in the skeletal structures of biominerals. Recently however, Ferguson et al. (EPSL, 2008) demonstrated that Mg/Ca ratios in foramanifera tests correlate more strongly with salinity than with temperature. Implications of this finding could be significant because 1) salinity oscillations are significant and 2) paleo temperatures are largely reconstructed from carbonate sediments that may have experienced substantial salinity fluctuations and 3) if salinity indeed enhances Mg/Ca, then temperatures during the Last Glacial Maximum (Adkins and Schrag, GRL, 2001) may have been overestimated. In a new study, we are conducting experiments to measure Mg/Ca signatures in calcites grown in solutions of variable salinities and constant chemical driving force, or constant Mg and Ca activities. By this approach, we test the hypothesis that high salinity environments promote uptake of Mg and if true, we will assess the origin of this behavior. In previous work we have demonstrated that 1) calcite takes up more Mg as growth rate is accelerated, particularly in the presence of rate-enhancing hydrophilic peptides and 2) biochemical environments that favor cation desolvation also promote Mg uptake. From these insights, we predict that changes in Mg/Ca signature will arise due to one of these two effects: the kinetic effect, or reductions in the barrier to Mg desolvation relative to Ca. Indeed, kinetic measurements of growth rate using in situ atomic force microscopy show that calcite growth rate increases significantly with ionic strength. Mg content in the overgrowths was analyzed by Secondary Ion Mass Spectrometry (SIMS) using a Cameca IMS-7f Geo magnetic sector instrument. In conducting a carefully designed array of experiments, we expect to establish a baseline to determine the extent by which salinity affects Mg/Ca signatures in a system where biological influences are absent.

  12. Empty seeds reduce seed predation by birds in Juniperus osteosperma

    E-print Network

    Fuentes, Marcelino

    Empty seeds reduce seed predation by birds in Juniperus osteosperma MARCELINO FUENTES1 and EUGENE W juniper (Juniperus osteosperma) is one of many plant species that produce large numbers of fruits to demonstrate discrimination based on seed ®lling at the level of whole plants. Keywords: empty seeds; Juniperus

  13. Strain localization in ultramylonitic calcite marbles by dislocation creep-accommodated grain boundary sliding

    NASA Astrophysics Data System (ADS)

    Rogowitz, Anna; Grasemann, Bernhard; Clancy White, Joseph

    2015-04-01

    Strain localization in monomineralic rocks is often associated with brittle precursors, resulting in stress and strain concentration, followed by grain size reduction and activation of grain-size-sensitive deformation mechanisms such as diffusion creep, grain boundary sliding and cataclastic flow. The aforementioned mechanisms typically tend to produce a random crystallographic orientation or a decrease in intensity of a pre-existing texture. However, reports of fine grained polycrystalline materials showing a preferred crystallographic orientation indicate a need for subsequent grain re-organization by either static annealing or the activation of additional deformation mechanisms in conjunction with grain boundary sliding. We present observations from an almost pure calcite marble layer from Syros Island (Cyclades, Greece) deformed in lower greenschist facies conditions. The presence of a crack (i.e. cross-cutting element) that rotated during shear resulted in the formation of a flanking structure. At the location of maximum displacement (120 cm) along the cross-cutting element, the marble is extremely fine grained (3 µm) leading to anticipation of deformation by grain-size-sensitive mechanisms. Detailed microstructural analysis of the highly strained (80 < gamma < 1000) calcite ultramylonite by optical microscopy, electron backscatter diffraction and scanning transmission electron microscopy show that recrystallization by bulging results in small, strain-free grains. The change in grain size appears to be concomitant with increased activity of independent grain boundary sliding as indicated by a random misorientation angle distribution. At the same time, dislocation multiplication through Frank-Read sources produces high mean dislocation density (~ 5x10^13 m^-2) as well as a weak primary CPO; the latter all argue that grain boundary sliding was accommodated by dislocation activity. Theoretical and experimental determined relationships (paleowattmeter, paleopiezometer, dislocation density) have been used to estimate the flow stress conditions. All of the applied relationships indicate differential stresses in a range between 80 and 200 MPa. Plotted in a deformation mechanism map for calcite, the data show that the ultramylonite was deformed at maximum strain rates of 10^-9 s^-1. Our study shows that the switch from dominantly dislocation creep to grain boundary sliding accommodated by dislocation activity corresponds to strain softening and can be an important strain localization process in calcite rocks, even at high strain rate (10^-9 s^-1) and low temperature (300 °C).

  14. Grain growth kinetics of dolomite, magnesite and calcite: a comparative study

    Microsoft Academic Search

    N. E. Davis; J. Newman; P. B. Wheelock; A. K. Kronenberg

    2011-01-01

    The rates of grain growth of stoichiometric dolomite [CaMg(CO3)2] and magnesite (MgCO3) have been measured at temperatures T of 700–800°C at a confining pressure P\\u000a c of 300 MPa, and compared with growth rates of calcite (CaCO3). Dry, fine-grained aggregates of the three carbonates were synthesized from high purity powders by hot isostatic pressing\\u000a (HIP); initial mean grain sizes of HIP-synthesized

  15. Process and apparatus for growing a crystal ribbon

    NASA Technical Reports Server (NTRS)

    Thornhill, J. W. (inventor)

    1984-01-01

    A process and apparatus is disclosed for growing a crystal ribbon of a substance of theoretically infinite length from a melt of the substance. A pair of fixedly positioned edge defining members are partially submerged into the melt so as to break the surface of the melt at a predetermined distance from one another. The edge defining members are wettable by the melt and the predetermined distance substantially corresponds to the width of the crystal ribbon to be grown. The crystal ribbon is grown by contacting the surface of the melt with a seed ribbon between the edge defining members whereby a meniscus of the melt is established on the seed ribbon. The meniscus is stabilized by the meniscus of the melt on the edge defining members. Pulling the seed crystal ribbon away from the melt results in continuous growth of the crystal ribbon.

  16. Influencing factors on the formation of the low minority carrier lifetime zone at the bottom of seed-assisted cast ingots

    NASA Astrophysics Data System (ADS)

    Zhong, Genxiang; Yu, Qinghua; Huang, Xinming; Liu, Lijun

    2014-09-01

    The effects of height of remaining seed, seed type, and crucible purity on the length of the low minority carrier lifetime zone (i.e., red zone) at the bottom of seed-assisted cast ingots were investigated. The red zone length at the bottom is proportional to the height of the remaining seeds. Only very little difference in the length of the bottom red zone was found in the quasi-single-crystal silicon (QSC-Si) bricks between using normal single-crystal seeds and recycled seeds, while the use of particle seeds resulted in a longer bottom red zone compared with using block seeds. Furthermore, a high-purity crucible does not result in a significant reduction in the height of bottom red zone in the QSC-Si ingot, although it results in a much shorter bottom red zone in the conventional mc-Si ingot.

  17. Seed Dispersal: Lemurs

    NSDL National Science Digital Library

    Pulse of the Planet

    2007-09-20

    Trees in Madagascar's forests have evolved traits that promote the dispersal of their seeds by lemurs. This two-minute radio program focuses on the interaction between forest plants and lemurs--the main seed dispersers in the forests. A guest scientist explains why lemurs ingest seeds that are large relative to their body size. He also notes that the fruits of Madagascar's trees have evolved to be strong smelling but drably colored in accordance with lemurs' keen sense of smell and poor vision. The program is available in text and audio formats. The latter includes audio of ring-tailed lemurs. Copyright 2005 Eisenhower National Clearinghouse

  18. SEED ARCHIVE AND STORAGE FACILITIES

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sugar beet seed storage facilities were updated, and seed is stored at 4C and 25% relative humidity. Over 15,000 packages of seed have been moved into the new storage facility. We used results from field scale germination studies to discard over 3,500 seedlots that showed no emergence. Current seed ...

  19. Seed output and the seed bank in Vallisneria americana (Hydrocharitaceae).

    PubMed

    Lokker, C; Lovett-Doust, L; Lovett-Doust, J

    1997-10-01

    Seed banks and sexual reproduction are known to be significant in colonization and re-establishment of some aquatic macrophyte communities. For highly clonal aquatic macrophytes, however, there is a lack of information on seed production and seed fate as compared with annual sexual species. The seed bank for three populations of Vallisneria americana in the Huron-Erie corridor of the Great Lakes was sampled and quantified in the spring of 1994, and related to seed production in the previous season at these sites. Seed deposition rates during 1994 were also assessed. Sites varied in the proportion of plants flowering and in their tertiary sex ratios, but did not differ in seed numbers produced per unit area. The size of the seed bank was not significantly related to the previous season's seed output, and estimates of seed deposition in the following year tended to be approximately tenfold greater than seed densities found in the seed bank. The stages between seed production and subsequent seed germination are generally very dynamic, with dispersal, mortality, and predation as likely regulating factors. The potential for seedling establishment in V. americana needs to be assessed more fully before the role of seeds in population processes can be determined. PMID:21708549

  20. MHD seed recovery/regeneration, Phase 2

    SciTech Connect

    Not Available

    1992-01-01

    Task I calls for the design, procurement, construction, and installation of the Seed Regeneration Proof-of-Concept Facility (SRPF) that will produce tonnage quantities of recyclable potassium formate seed at a design rate of 250 lb/hr for testing in the channel at the CDIF while collecting data that will be used to upgrade the design of a 300 MW[sub t] system. Approximately 12 tons of KCOOH (dry basis) as 70--75 wt % solution have been produced. The long-term plant securing operations which were started in May were completed during this reporting period. Securing operations included both the front end of the plant (potassium sulfate reaction and solids separation/washing units) and the evaporator/crystallizer. In addition, weekly preventative maintenance was performed. TRW is awaiting word from the CDIF in Montana that it is alright to ship the 41 drums of concentrated potassium formate final product to Montana.

  1. Nitrogen and hydrogen in bulk single-crystal ZnO S.J. Jokela, M.C. Tarun, M.D. McCluskey

    E-print Network

    McCluskey, Matthew

    .elsevier.com/locate/physb Physica B Fig. 1. Schematic diagram of the CVT growth system. Single-crystal ZnO is grown on a seedO as a seed, we obtained bulk single-crystal growth. The N­H bond-stretching mode gives rise to an IR is carefully removed. If a seed crystal is to be used, it must be attached and in good thermal contact

  2. Implications of the lack of desiccation tolerance in recalcitrant seeds

    PubMed Central

    Berjak, Patricia; Pammenter, Norman W.

    2013-01-01

    A suite of interacting processes and mechanisms enables tolerance of desiccation and storage (conservation) of orthodox seeds in the dry state. While this is a long-term option under optimized conditions, dry orthodox seeds are not immortal, with life spans having been characterized as short, intermediate and long. Factors facilitating desiccation tolerance are metabolic “switch-off” and intracellular dedifferentiation. Recalcitrant seeds lack these mechanisms, contributing significantly to their desiccation sensitivity. Consequently, recalcitrant seeds, which are shed at high water contents, can be stored only in the short-term, under conditions not allowing dehydration. The periods of such hydrated storage are constrained by germination that occurs without the need for extraneous water, and the proliferation of seed-associated fungi. Cryopreservation is viewed as the only option for long-term conservation of the germplasm of recalcitrant-seeded species. This is not easily achieved, as each of the necessary procedures imposes oxidative damage. Intact recalcitrant seeds cannot be cryopreserved, the common practice being to use excised embryos or embryonic axes as explants. Dehydration is a necessary procedure prior to exposure to cryogenic temperatures, but this is associated with metabolism-linked injury mediated by uncontrolled reactive oxygen species generation and failing anti-oxidant systems. While the extent to which this occurs can be curtailed by maximizing drying rate (flash drying) it cannot be completely obviated. Explant cooling for, and rewarming after, cryostorage must necessarily be rapid, to avoid ice crystallization. The ramifications of desiccation sensitivity are discussed, as are problems involved in cryostorage, particularly those accompanying dehydration and damage consequent upon ice crystallization. While desiccation sensitivity is a “fact” of seed recalcitrance, resolutions of the difficulties involved germplasm conservation are possible as discussed. PMID:24319450

  3. An innovative approach for pseudoboehmite precipitation from seeded sodium aluminate solutions

    Microsoft Academic Search

    Weiquan Cai; Huiquan Li; Guangxu Zhang

    2010-01-01

    Precipitation of boehmite from seeded sodium aluminate (SA) solutions for production of smelter grade alumina by calcination is in the early stage of development. However, the reported boehmites are usually well crystallized and actually most boehmites for activated aluminas are poorly crystallized and less ordered forms, which is also called pseudoboehmite. In the present study, an attempt has been made

  4. Method for horizontally growing ribbon crystal

    NASA Technical Reports Server (NTRS)

    Kudo, B.

    1980-01-01

    A high speed method for forming ribbon crystal of desired width and thickness is characterized by drawing out the ribbon through a space whose distance is 5.7 times that of the thickness of the grown ribbon. The ribbon is drawn out between the molten body of the lower surface and the tip of the upper surface of the seed crystal and growing crystal. The ribbon growing at the tip of the seed crystal is drawn out horizontally and centrifugally by controlling the amount of cooling and heating. The temperature is maintained about equal to the upper surface of the outlets from which the molten substance is drawn, at least in certain portions of the crucible rim, the rim is elevated to prevent dropping of the molten raw material.

  5. A Sr-isotopic comparison between thermal waters, rocks, and hydrothermal calcites, Long Valley caldera, California

    USGS Publications Warehouse

    Goff, F.; Wollenberg, H.A.; Brookins, D.C.; Kistler, R.W.

    1991-01-01

    The 87Sr/86Sr values of thermal waters and hydrothermal calcites of the Long Valley caldera geothermal system are more radiogenic than those of young intracaldera volcanic rocks. Five thermal waters display 87Sr/86Sr of 0.7081-0.7078 but show systematically lighter values from west to east in the direction of lateral flow. We believe the decrease in ratio from west to east signifies increased interaction of deeply circulating thermal water with relatively fresh volcanic rocks filling the caldera depression. All types of pre-, syn-, and post-caldera volcanic rocks in the west and central caldera have (87Sr/86Sr)m between about 0.7060 and 0.7072 and values for Sierra Nevada granodiorites adjacent to the caldera are similar. Sierran pre-intrusive metavolcanic and metasedimentary rocks can have considerably higher Sr-isotope ratios (0.7061-0.7246 and 0.7090-0.7250, respectively). Hydrothermally altered volcanic rocks inside the caldera have (87Sr/86Sr)m slightly heavier than their fresh volcanic equivalents and hydrothermal calcites (0.7068-0.7105) occupy a midrange of values between the volcanic/plutonic rocks and the Sierran metamorphic rocks. These data indicate that the Long Valley geothermal reservoir is first equilibrated in a basement complex that contains at least some metasedimentary rocks. Reequilibration of Sr-isotope ratios to lower values occurs in thermal waters as convecting geothermal fluids flow through the isotopically lighter volcanic rocks of the caldera fill. ?? 1991.

  6. UNSATURATED ZONE CALCITE 813C EVIDENCE OF SOUTHERN NEVADA CLIMATES DURING THE PAST 9 MILLION YEARS

    SciTech Connect

    JOSEPH F. WHELAN AND RICHARD J. MOSCATI

    1998-01-26

    Yucca Mountain, Nevada, is presently the object of intense study as a potential permanent repository for the Nation's high-level radioactive wastes. The mountain consists of a thick sequence of volcanic tuffs in which the depth to the water table ranges from 500 to 700 meters below the land surface. This thick unsaturated zone (UZ), which would host the projected repository, coupled with the present-day arid to semi-arid environment, is considered a positive argument for the site. Evaluation of the site includes defining the relationship between climate variability, as the input function or driver of site- and regional-scale ground-water flow, and the possible transport and release of radionuclides. Secondary calcite and opal have been deposited in the UZ by meteoric waters that infiltrated through overlying soils and percolated through the tuffs. The oxygen isotopic composition ({delta}{sup 18}O values) of these minerals reflect contemporaneous meteoric waters and the {delta}{sup 13}C values reflect soil organic matter, and hence the resident plant community, at the time of infiltration (Whelan et al., 1994). Recent U/Pb age determinations of opal in these occurrences allows the {delta}{sup 13}C values of associated calcite to be used to reconstruct general climate variations during the past 9 M.y.

  7. Continuous 500,000-year climate record from vein calcite in Devils Hole, Nevada

    SciTech Connect

    Winograd, I.J.; Coplen, T.B.; Landwehr, J.M.; Revesz, K.M. (U.S. Geological Survey, Reston, VA (United States)); Riggs, A.C.; Ludwig, K.R.; Szabo, B.J. (U.S. Geological Survey, Lakewood, CO (United States)); Kolesar, P.T. (Utah State Univ., Logan, UT (United States))

    1992-10-09

    Oxygen-18 ({delta}{sup 18}O) variations in a 36-centimeter-long core (DH-11) of vein calcite from Devils Hole, Nevada, yield an uninterrupted 500,000-year paleotemperature record that closely mimics all major features in the Vostok (Antarctica) paleotemperature and marine {delta}{sup 18}O ice-volume records. The chronology for this continental record is based on 21 replicated mass-spectrometric uranium-series dates. Between the middle and latest Pleistocene, the duration of the last four glacial cycles recorded in the calcite increased from 80,000 to 130,000 years; this variation suggests that major climate changes were aperiodic. The timing of specific climatic events indicates that orbitally controlled variations in solar insolation were not a major factor in trigering deglaciations. Interglacial climates lasted about 20,000 years. Collectively, these observations are inconsistent with the Milankovitch hypothesis for the origin of the Pleistocene glacial cycles but they are consistent with the thesis that these cycles originated from internal nonlinear feedbacks within the atmosphere-ice sheet-ocean system.

  8. A theoretical approach to the kinetics of calcite ? aragonite transition: application to laboratory experiments

    NASA Astrophysics Data System (ADS)

    Madon, M.; Gillet, Ph.

    1984-03-01

    A theoretical approach to the calcite ? aragonite transformation is presented for the case of a dislocation glide mechanism obeying first-order kinetics. The kinetic parameters are determined from recent experimental data from the literature; the sensitivity of the model to these and other parameters like the grain size and the deviatoric stresses are discussed. The model results in the definition of what could be the actual transformation domains of the CaCO 3 polymorphs in the ( P,T) plane. These domains are different from the classical ones, i.e. different from the stability fields defined with respect to Clapeyron's curve; they can evolve in the ( P,T) plane when a deviatoric stress is applied to the system. In this case, we can define a domain in which the two senses of the calcite ? aragonite transition are activated simultaneously. The application of the model to laboratory experiments needs the integration of the kinetic differential equation ( K varying with P and T). Using this method, we demonstrate the role of ( P,T,t) path on reaction rate and the role of experimental uncertainties on the reaction parameters K and n. Finally, we discuss the problem of the synthesis of polymorphs out of their stability field and of their formation by grinding; these problems, difficult to tackle in terms of diffusion, can be approached with the proposed dislocation transformation kinetic model.

  9. Continuous 500,000-year climate record from vein calcite in Devils Hole, Nevada

    USGS Publications Warehouse

    Winograd, I.J.; Coplen, T.B.; Landwehr, J.M.; Riggs, A.C.; Ludwig, K. R.; Szabo, B. J.; Kolesar, Peter T.; Revesz, K.M.

    1992-01-01

    Oxygen-18 (??18O) variations in a 36-centimeter-long core (DH-11) of vein calcite from Devils Hole, Nevada, yield an uninterrupted 500,000-year paleotemperature record that closely mimics all major features in the Vostok (Antarctica) paleotemperature and marine ??18O ice-volume records. The chronology for this continental record is based on 21 replicated mass-spectrometric uranium-series dates. Between the middle and latest Pleistocene, the duration of the last four glacial cycles recorded in the calcite increased from 80,000 to 130,000 years; this variation suggests that major climate changes were aperiodic. The timing of specific climatic events indicates that orbitally controlled variations in solar insolation were not a major factor in triggering deglaciations. Interglacial climates lasted about 20,000 years. Collectively, these observations are inconsistent with the Milankovitch hypothesis for the origin of the Pleistocene glacial cycles but they are consistent with the thesis that these cycles originated from internal nonlinear feedbacks within the atmosphere-ice sheet-ocean system.

  10. Calcite-graphite thermometry of the Franklin Marble, New Jersey Highlands

    USGS Publications Warehouse

    Peck, W.H.; Volkert, R.A.; Meredith, M.T.; Rader, E.L.

    2006-01-01

    We present new stable-isotope data for the Mesoproterozoic Franklin Marble from outcrops along an 80-km traverse parallel to and across strike of the structural grain of the western New Jersey Highlands. Calcite and dolomite from marble have an average ??13C of 0.35??? ?? 0.73??? PDB (n = 46) and a more limited range than other Mesoproterozoic marbles from the Adirondacks and the Canadian Grenville Province. The small range of ??13C values from the New Jersey samples is consistent with the preservation of a primary marine isotopic signature and limited postdepositional isotopic modification, except proximal to Zn or Fe ore deposits and fault zones. Fractionations between calcite and well-formed graphite (??13C[Cal-Gr]) for analyzed Franklin Marble samples average 3.31???. ?? 0.25??? (n = 34), and dolomite-graphite fractionations average 3.07??? ?? 0.30??? (n = 6). Taken together, these indicate an average temperature of 769?? ?? 43??C during metamorphism associated with the Ottawan Orogeny in the New Jersey Highlands. Thus, carbon isotope fractionations demonstrate that the Franklin Marble was metamorphosed at granulite facies conditions. Metamorphic temperatures are relatively constant for the area sampled and overprint the metamorphosed carbonatehosted Zn-Fe-Mn ore deposits. The results of this study support recent work proposing that pressure and temperature conditions during Ottawan orogenesis did not vary greatly across faults that partition the Highlands into structural blocks. ?? 2006 by The University of Chicago. All rights reserved.

  11. A revised model for microbially induced calcite precipitation: Improvements and new insights based on recent experiments

    NASA Astrophysics Data System (ADS)

    Hommel, Johannes; Lauchnor, Ellen; Phillips, Adrienne; Gerlach, Robin; Cunningham, Alfred B.; Helmig, Rainer; Ebigbo, Anozie; Class, Holger

    2015-05-01

    The model for microbially induced calcite precipitation (MICP) published by Ebigbo et al. (2012) has been improved based on new insights obtained from experiments and model calibration. The challenge in constructing a predictive model for permeability reduction in the underground with MICP is the quantification of the complex interaction between flow, transport, biofilm growth, and reaction kinetics. New data from Lauchnor et al. (2015) on whole-cell ureolysis kinetics from batch experiments were incorporated into the model, which has allowed for a more precise quantification of the relevant parameters as well as a simplification of the reaction kinetics in the equations of the model. Further, the model has been calibrated objectively by inverse modeling using quasi-1D column experiments and a radial flow experiment. From the postprocessing of the inverse modeling, a comprehensive sensitivity analysis has been performed with focus on the model input parameters that were fitted in the course of the model calibration. It reveals that calcite precipitation and concentrations of NH4+ and Ca2+ are particularly sensitive to parameters associated with the ureolysis rate and the attachment behavior of biomass. Based on the determined sensitivities and the ranges of values for the estimated parameters in the inversion, it is possible to identify focal areas where further research can have a high impact toward improving the understanding and engineering of MICP.

  12. Bacterial bio-mediated calcite precipitation for monumental stones conservation: methods of evaluation.

    PubMed

    Tiano, P; Biagiotti, L; Mastromei, G

    1999-05-01

    The weathering of monumental stones is a complex process inserted in the more general 'matter transformation cycle' operated by physical, chemical and biological factors. The consequence of these combined actions is a loss of cohesion with dwindling and scaling of stone material and the induction of a progressive mineral matrix dissolution. In the case of calcareous stones, calcite leaching increases the material porosity and decreases its mechanical features with a general weakening of the superficial structural strength. Attempts to stop, or at least to slow down, deterioration of monumental stones has been made by conservative treatments with both inorganic or organic products. More recent studies show a new approach to hinder these phenomena by inducing a bio-mediated precipitation of calcite directly inside the stone porosity. This can be achieved either through the application of organic matrix macromolecules extracted from sea shells or of living bacteria. The effectiveness of the treatment using calcinogenic bacteria has been evaluated with laboratory tests specifically developed to evaluate the parameters such as : porosity, superficial strength and chromatic changes, influenced by the treatment itself. The results obtained seem to indicate that this type of treatment might not be suitable for monumental stone conservation. PMID:10353808

  13. The rehabilitation of monitoring wells clogged by calcite precipitation and drilling mud

    SciTech Connect

    Kroening, D.E.; Snipes, D.S.; Brame, S.E.; Hodges, R.A.; Price, V.; Temples, T.J.

    1996-08-01

    Based on aquifer performance tests, 13 out of 15 wells situated at the Mixed Waste Disposal (MWD) area located at the Savannah River site, South Carolina, exhibited high skin factors and low well efficiencies indicative of severely damaged wells. The use of damaged wells in aquifer testing can lead to inaccurate determinations of aquifer properties, and such wells are unusable in future remediation programs. Moreover, damaged wells can go dry during purging, thus compromising sample collection. Pump tests, chemical analyses, and biological investigations revealed that the poor well performance at MWD was attributable to calcite precipitation on the well screen and drilling mud in the filter pack. The calcite problem resulted from improper well installation, and the drilling mud in the filter pack was due to inadequate well development. Experimental rehabilitation procedures employed on two wells, MWD 5A and 1A, included acidification, swabbing, introduction of surfactants, and surging. Treatment of the wells substantially improved well yields, skin factors, and well efficiencies. Moreover, well rehabilitation was determined to be a reasonable alternative to drilling new wells at the MWD wellfield.

  14. Magneto-optical properties of biogenic photonic crystals in algae

    SciTech Connect

    Iwasaka, M., E-mail: iwasaka-m@umin.ac.jp [Chiba University, 1-33 Yayoicho, Inage-ku, 263-8522 Chiba (Japan); Japan Science and Technology Agency, PRESTO, 4-1-8 Honcho, Kawaguchi 332-0012 Saitama (Japan); Mizukawa, Y. [Chiba University, 1-33 Yayoicho, Inage-ku, 263-8522 Chiba (Japan)

    2014-05-07

    In the present study, the effects of strong static magnetic fields on the structural colors of the cell covering crystals on a microalgae, coccolithophore, were investigated. The coccolithophore, Emiliania huxleyi, generates a precise assembly of calcite crystals called coccoliths by biomineralization. The coccoliths attached to the cells exhibited structural colors under side light illumination, and the colors underwent dynamic transitions when the magnetic fields were changed between 0?T and 5?T, probably due to diamagnetically induced changes of their inclination under the magnetic fields. The specific light-scattering property of individual coccoliths separated from the cells was also observed. Light scattering from a condensed suspension of coccoliths drastically decreased when magnetic fields of more than 4?T were applied parallel to the direction of observation. The magnetically aligned cell-covering crystals of the coccolithophores exhibited the properties of both a photonic crystal and a minimum micromirror.

  15. Rapid Carbonation for Calcite from a Solid-Liquid-Gas System with an Imidazolium-Based Ionic Liquid

    PubMed Central

    Ibrahim, Abdul-Rauf; Vuningoma, Jean Bosco; Huang, Yan; Wang, Hongtao; Li, Jun

    2014-01-01

    Aqueous carbonation of Ca(OH)2 is a complex process that produces calcite with scalenohedral calcite phases and characterized by inadequate carbonate species for effective carbonation due to the poor dissolution of CO2 in water. Consequently, we report a solid-liquid-gas carbonation system with an ionic liquid (IL), 1-butyl-3-methylimidazolium bromide, in view of enhancing the reaction of CO2 with Ca(OH)2. The use of the IL increased the solubility of CO2 in the aqueous environment and enhanced the transport of the reactive species (Ca2+ and CO32?) and products. The presence of the IL also avoided the formation of the CaCO3 protective and passivation layer and ensured high carbonation yields, as well as the production of stoichiometric rhombohedral calcite phases in a short time. PMID:24968273

  16. Crystal growth rates and optical resolution of DL-methionine hydrochloride by preferential crystallization from aqueous solution

    NASA Astrophysics Data System (ADS)

    Srimahaprom, Watcharakarn; Flood, Adrian E.

    2013-01-01

    Optical resolution of DL-methionine hydrochloride (DL-met·HCl) by preferential crystallization was studied for the purification of L-met·HCl (the desired enantiomer) from supersaturated solutions of DL-met·HCl. The nucleation thresholds (NT) of DL-met·HCl affect the maximum resolution time suitable for preferential crystallization and also the percentage purity of the product crystals. Crystal growth rates of L-met·HCl single crystals both in supersaturated solutions of DL-met·HCl and in supersaturated solutions of pure L-met·HCl were measured in order to model the preferential crystallization more effectively. Results showed that the growth rate depends strongly on the relative supersaturation (especially from pure L-met·HCl solutions), that there is a wide crystal growth rate distribution in growth from both types of solution, and that the growth is faster from pure L-met·HCl solutions, as expected. A batch crystallizer seeded with L-met·HCl crystals was used to study the preferential crystallization, and to study the behavior of purity decrease of the product crystals during the crystallization process. The purity of the L-met·HCl product decreased to the equilibrium value over time, with almost no plateau at 100% purity (as is hoped for in preferential crystallizations). This is explainable by the very short induction times for nucleation in these solutions, and also that the L-met·HCl seed crystals may act as a template for the nucleation of the counter-enantiomer.

  17. Evaluating Cotton Seed Quality

    E-print Network

    Boman, Randy

    2005-10-05

    High-quality cotton seed is critical for establishing good stands. Over the last several years, producers have scrutinized costs and benefits of numerous new cotton varieties. With the increase in cost of most current cotton varieties and the use...

  18. Fishing for Seeds.

    ERIC Educational Resources Information Center

    Science and Children, 2001

    2001-01-01

    Describes a method to collect seeds that are dispersed from weeds while avoiding some outdoor hazards such as rough terrain or animals. Describes a plan for creating a weed fishing pole and includes a materials list. (SAH)

  19. Evaluating Cotton Seed Quality 

    E-print Network

    Boman, Randy

    2005-10-05

    High-quality cotton seed is critical for establishing good stands. Over the last several years, producers have scrutinized costs and benefits of numerous new cotton varieties. With the increase in cost of most current cotton varieties and the use...

  20. Easy PEAsy Seed Germination

    NSDL National Science Digital Library

    2012-04-09

    In this activity, learners determine the necessary conditions for pea seed germination. This activity encourages learners to make predictions and think about how they might investigate the effects of variables like light, temperature, and moisture.