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1

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

USGS Publications Warehouse

A highly reproducible seeded growth technique was used to study calcite crystallization from calcium bicarbonate solutions at 25??C and fixed carbon dioxide partial pressures between 0.03 and 0.3 atm. The results are not consistent with empirical crystallization models that have successfully described calcite growth at low PCO2 (< 10-3 atm). Good agreement was found between observed crystallization rates and those calculated from the calcite dissolution rate law and mechanism proposed by Plummer et al. (1978). ?? 1981.

Reddy, M.M.; Plummer, L.N.; Busenberg, E.

1981-01-01

2

Calcite crystal growth rate inhibition by polycarboxylic acids  

USGS Publications Warehouse

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

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

2001-01-01

3

Molecular Expressions: Optical Microscopy Primer - Birefringence in Calcite Crystals  

NSDL National Science Digital Library

This item is an interactive Java simulation for students of introductory physics or optics relating to birefringence. It features a virtual calcite crystal superimposed over the word "Birefringence". Due to the refractive properties of this type of crystal, the letters appear as a ghosted double image. The user can rotate the crystal and the polarizer to alter the transmission axis. This item is part of a larger collection of materials on introductory optics developed by the National High Magnetic Field Laboratory.

Davidson, Michael; Parry-Hill, Matthew J.; Murphy, Douglas B.; Spring, Kenneth R.; Long, John

2008-08-23

4

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

E-print Network

Calcite crystal growth orientation: implications for trace metal uptake into coccoliths V. E. PAYNE inducing specific orientations of calcite crystal growth can cause the enrichment of cations larger than Ca growth on obtuse kink sites, causing calcite crystals elongated along their c-axes to form in a mechanism

Benning, Liane G.

5

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

E-print Network

The kinetics and mechanisms of amorphous calcium carbonate (ACC) crystallization to calcite, via calcium carbonate (ACC) crystallization to calcite, via vaterite, were studied at a range formation of calcium carbonate minerals (e.g. calcite) occurs in a wide range of natural envi- ronments (e

Benning, Liane G.

6

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

E-print Network

Selenium incorporation into calcite and its effect on crystal growth: An atomic force microscopy Crystal growth Selenium The atomic processes leading to calcite growth are still debated. The presence of foreign impurities in solution is known to change the rate of step propagation during growth as well

Montes-Hernandez, German

7

Author's personal copy Selenium incorporation into calcite and its effect on crystal growth: An atomic force  

E-print Network

Author's personal copy Selenium incorporation into calcite and its effect on crystal growth Atomic force microscopy Crystal growth Selenium The atomic processes leading to calcite growth are still during growth as well as the growth mechanism. Among trace elements, selenium, in the form of oxyanions

8

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

PubMed Central

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

Murai, Rie

2013-01-01

9

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

USGS Publications Warehouse

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.

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

2000-01-01

10

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

SciTech Connect

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

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

2009-01-01

11

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

SciTech Connect

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

Kim, Kyungil; Uysal, Ahmet; Kewalramani, Sumit; Stripe, Benjamin; Dutta, Pulak; (NWU); (BNL)

2009-04-22

12

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

SciTech Connect

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.

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

13

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

NASA Astrophysics Data System (ADS)

A growing number of classes of organic (macro)molecular materials have been trapped into inorganic crystalline hosts, such as calcite single crystals, without significantly disrupting their crystalline lattices. Inclusion of an organic phase plays a key role in enhancing the mechanical properties of the crystals, which are believed to share structural features with biogenic minerals. Here we report the synthesis and mechanical characterization of composite calcite/SWCNT-COOH single crystals. Once entrapped into the crystals SWCNT-COOH appeared both as aggregates of entangled bundles and nanoropes. Their observation was possible only after crystal etching, fracture or FIB (focused ion beam) cross-sectioning. SWCNT-COOHs occupied a small volume fraction and were randomly distributed into the host crystal. They did not strongly affect the crystal morphology. However, although the Young's modulus of composite calcite/SWCNT-COOH single crystals was similar to that of pure calcite their hardness increased by about 20%. Thus, SWCNT-COOHs provide an obstacle against the dislocation-mediated propagation of plastic deformation in the crystalline slip systems, in analogy with the well-known hardness increase in fiber-reinforced composites.A growing number of classes of organic (macro)molecular materials have been trapped into inorganic crystalline hosts, such as calcite single crystals, without significantly disrupting their crystalline lattices. Inclusion of an organic phase plays a key role in enhancing the mechanical properties of the crystals, which are believed to share structural features with biogenic minerals. Here we report the synthesis and mechanical characterization of composite calcite/SWCNT-COOH single crystals. Once entrapped into the crystals SWCNT-COOH appeared both as aggregates of entangled bundles and nanoropes. Their observation was possible only after crystal etching, fracture or FIB (focused ion beam) cross-sectioning. SWCNT-COOHs occupied a small volume fraction and were randomly distributed into the host crystal. They did not strongly affect the crystal morphology. However, although the Young's modulus of composite calcite/SWCNT-COOH single crystals was similar to that of pure calcite their hardness increased by about 20%. Thus, SWCNT-COOHs provide an obstacle against the dislocation-mediated propagation of plastic deformation in the crystalline slip systems, in analogy with the well-known hardness increase in fiber-reinforced composites. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr01568h

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

2013-07-01

14

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

SciTech Connect

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.

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

15

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

Microsoft Academic Search

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

Amitai Katz

1973-01-01

16

SEMI-BATCH CRYSTALLIZATION OF GYPSUM FROM CALCITE AND SULFURIC ACID  

E-print Network

SEMI-BATCH CRYSTALLIZATION OF GYPSUM FROM CALCITE AND SULFURIC ACID F. Bard, D. Garcia , G. Févotte or reusing some compounds they contain in other production processes. The latter is of great interest, both- scale installation modeling the neutralization of a sulphuric acid solution by injection of a diluted

Paris-Sud XI, Université de

17

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

SciTech Connect

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.

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

2000-05-01

18

In situ study of boron partitioning between calcite and fluid at different crystal growth rates  

NASA Astrophysics Data System (ADS)

The boron isotopic and chemical content of carbonates (expressed as ?11B and B/Ca ratios) have been proposed as proxies for seawater carbonate system parameters. Thermodynamic and kinetic effects on ?11B and B partitioning are not yet fully constrained, underscoring the importance of exploring possible effects of growth rate on boron incorporation in synthetic calcium carbonate minerals, which is the focus of this study. Secondary Ion Mass Spectrometry (SIMS) measurements of B/Ca and ?11B were performed on single crystal of calcite synthesized by diffusion of CO2 under controlled conditions from a solution of NH4Cl-CaCl2 doped with boron. Growth rates of calcite (V, nm/s) within crystals grown isothermally at 24.6 C were monitored by sequentially spiking calcite-precipitating fluids with rare earth element (REE) dopants. The REE were analyzed with SIMS at spots that match those locations where B/Ca and ?11B ratios were measured. Values for the boron Nernst partition coefficient, defined as DB = B(calcite)/B(fluid), increase from 0.5 (pHNBS = 8.15) to 0.9 (pH = 8.00) with values of V increasing from 0.04 to 0.13 nm/s. For ?11B behavior, it was not possible to draw conclusive results due to the analytical error (2.2; 2?). pH effects on DB during calcite precipitation, associated with an increase in pH from 8.00 to 8.15, appear to be masked by the competing effects of changing V. We conclude that over the range of growth rates and other conditions investigated in this study, growth rate effects on B partitioning need to be accounted for when using B/Ca ratios in biogenic calcite as a proxy for seawater carbonate system parameters.

Gabitov, Rinat I.; Rollion-Bard, Claire; Tripati, Aradhna; Sadekov, Aleksey

2014-07-01

19

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

NASA Astrophysics Data System (ADS)

The mechanisms governing selective CaCO3 crystal nucleation in living organisms remain unclear. For example, nacreous layers from the inner surfaces of shells are built as brick-and-mortar complexes of plate-like aragonite single crystals and organic layers. Unstable [001] surfaces of calcite columns in prismatic layers are also stabilized by organic molecules. Biogenic calcite crystals show different morphologies compared to geological calcite minerals. Langmuir monolayers are used as structured templates in simulated biomineralization from CaCO3 supersaturated subphases. But pure or mixed Langmuir monolayers do not mimic the nucleation sites of aspartic-rich proteins found within real biominerals. It has previously been shown that there is organic-inorganic lattice relaxation in the cases of BaF2 and hydrocerussite (2PbCO3Pb(OH) 2) nucleation under fatty (carboxylate) acid with preferred orientation of crystals, but no lattice match is observed during CaCO3 crystallization under fatty acid Langmuir monolayers. Overall, geometric influences such as structural match between the interfacial lattices and the interactions between monolayer headgroups and aqueous ions do not guarantee any well-defined orientation of CaCO3 crystallization. CaCO3 mineralization on self-assembled monolayers on metal and alloy substrates have achieved higher degrees of orientations, even though molecules in Langmuir monolayers are better ordered than in self-assembled monolayers. Until now, Langmuir monolayer experiments have emphasized only the function of the acidic proteins. To better mimic the real organic template, it is important to include the hydrophobic and polyelectrolyte characteristics of real organic templates in shells. The organic matrix in actual shells contains hydrophobic silk fibroin (which is hydrophobic) and polyelectrolytes. Some acidic proteins reside on the surface of silk fibroins. There is also semi-crystalline beta-chitin structure whose function has not been fully understood. To better simulate the biological system, chitosan was added to the aqueous subphase. The crystallization processes were monitored using in-situ Grazing incidence X-ray diffraction (GID). Scanning electron microscopy (SEM) was used to perform morphological studies on grown crystals. Dissolved chitosan causes distinct concentration-dependent changes in orientation, shape and morphology of the calcite crystals nucleating under acid and sulfate monolayers. Our results suggest that polyelectrolytes may play essential roles in controlling the growth of biogenic calcite crystals.

Kim, Kyungil

20

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

PubMed Central

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

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

2003-01-01

21

Correlation between anisotropy and lattice distortions in single crystal calcite nanowires grown in confinement.  

PubMed

Growing nanostructures in confinement allows for the control of their shape, size and structure, as required in many technological applications. We investigated the crystal structure and morphology of calcite nanowires, precipitated in the pores of track-etch membranes, by employing transmission electron microscopy and selected area electron diffraction (SAED). The data showed that the nanowires show no preferred growth orientation and that the crystallographic orientation rotated along the length of the nanowire, with lattice rotation angles of several degrees per micrometer. Finite element calculations indicated that the rotation is caused by the anisotropic crystallographic nature of the calcite mineral, the nanoscale diameter of the wires and the confined space provided by the membrane pore. This phenomenon should also be observed in other single crystal nanowires made from anisotropic materials, which could offer the potential of generating nanostructures with tailored optical, electronic and mechanical properties. PMID:24644031

Verch, Andreas; Ct, Alexander S; Darkins, Robert; Kim, Yi-Yeoun; van de Locht, Rene; Meldrum, Fiona C; Duffy, Dorothy M; Krger, Roland

2014-07-01

22

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

23

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

USGS Publications Warehouse

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.

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

2000-01-01

24

Development of artificial seed crystal for crystallization of calcium phosphate.  

PubMed

An artifical seed crystal material consisting of calcium silicate hydrate (5CaO x 6SiO2 x 5H2O : tobermorite crystals) applicable for phosphorus removal by crystallization was developed. Card-house shaped tobermorite crystals were developed on the seed material where orthophosphate crystallized as a calcium phosphate. The seed material can be manufactured by mixing siliceous and calcareous raw materials, pelletizing and subsequent autoclaving. Laboratory experiments were conducted to apply the new developed seed crystal material in the phosphorus recovery from sludge sidestreams of a wastewater treatment plant. In this crystallization process, the performance the carbon dioxide degassingprocess usually carried out when applying crystallization was not necessary, the hydroxyapatite was able to crystallize at a pH of 8.0 to 8.5 without precipitation of calcium carbonates. In the treatment of a sidestream with orthophosphate concentrations of 50 mgl(-1) and COD concentrations between 200 to 400 mgl(-1), phosphorus removal efficiencies ranging from 75 to 85% were observed. The seed crystal material was collected after the laboratory experiments and the chemical estimation and the germination test for agricultural reuse were performed. As a result, it was shown that the hydroxyapatite precipitated on the seed material had a 100% fusibility to soil and had characteristics to be a good nutrient source as a fertilizer for plants. PMID:11804345

Moriyama, K; Kojima, T; Minawa, Y; Matsumoto, S; Nakamachi, K

2001-11-01

25

Optical measurements to determine the thickness of calcite crystals and the mass of thin carbonate particles such as coccoliths.  

PubMed

We describe a procedure for measuring the thickness and mass of calcite particles that works for most calcite particles <4.5-?m thick. The calcite particles are observed in cross-polarized light, which enables the light transmitted through the calcite particles to be correlated with their thickness. Three polarizing planes are used to minimize the darkening of crystals at some orientations (black cross). This allows direct measurement of the thickness without recourse to a transfer function. This procedure has been used recently to determine the degree of calcification of coccoliths, which provides an indicator of ocean acidification. It takes only a few minutes per sample, and it is an improvement over the former protocol, which did not allow measurement of the thickness and mass of particles thicker than 1.5 ?m. PMID:24556786

Beaufort, Luc; Barbarin, Nicolas; Gally, Yves

2014-03-01

26

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

NASA Astrophysics Data System (ADS)

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

Gzquez, Fernando; Calaforra, Jos-Mara; Forti, Paolo; De Waele, Jo; Sanna, Laura; Rull, Fernando; Sanz, Aurelio

2013-09-01

27

Vertical Bridgman growth of sapphire-Seed crystal shapes and seeding characteristics  

NASA Astrophysics Data System (ADS)

The growth of sapphire by the traditional vertical Bridgman (VB) method was studied by using various shapes of seed crystals and tungsten (W) crucibles shaped to match the seeds. Approximately 2-in. diameter, c-axis sapphire single crystals were reproducibly grown from three kinds of seed: thin, tapered and full diameter. Factors relating seed type to single-crystal growth are discussed, including the reproducibility of seeding processes, and the generation and elimination of low-angle grain boundaries (LAGBs). What was learned facilitated the subsequent growth of large-diameter, 3-, 4- and 6-in., c-axis single-crystal sapphires from full-diameter seeds.

Hoshikawa, K.; Osada, J.; Saitou, Y.; Ohba, E.; Miyagawa, C.; Kobayashi, T.; Yanagisawa, J.; Shinozuka, M.; Kanno, K.

2014-06-01

28

Device for isolation of seed crystals during processing of solution  

DOEpatents

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.

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

1999-05-18

29

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)

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.

Bonny, Sandy M.; Jones, Brian

2008-01-01

30

Temperature-Controlled Support for a Seed Crystal  

NASA Technical Reports Server (NTRS)

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

Reeve, J. L.

1982-01-01

31

Device for isolation of seed crystals during processing of solution  

DOEpatents

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.

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

1999-01-01

32

Trigonal Dendritic Calcite Crystals Forming from Hot Spring Waters at Waikite, North Island, New Zealand  

Microsoft Academic Search

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

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

2000-01-01

33

High surface area calcite  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

34

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

Microsoft Academic Search

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

Norihito Doki; Noriaki Kubota; Akira Sato; Masaaki Yokota

2001-01-01

35

Evolution and the Calcite Eye Lens  

E-print Network

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.

Vernon L. Williams

2013-04-03

36

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

37

Production of Calcite (Calcium Carbonate) Crystals by Soil Bacteria is a General Phenomenon  

Microsoft Academic Search

CERTAIN bacteria form crystals from the solutes in their aqueous environment, and some authors have associated this activity with the extensive deposits of CaCO3 in such places as the Grand Bahama, in spite of the belief that physicochemical effects, such as rapid changes in pH, salinity and temperature, are responsible1-4. Drew5 isolated a denitrifying bacterium able to form CaCO3 crystals

E. Boquet; A. Boronat; A. Ramos-Cormenzana

1973-01-01

38

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

USGS Publications Warehouse

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.

Busenberg, E.; Niel, Plummer L.

1985-01-01

39

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

Calcite crystallization rates are characterized using a constant solution composition at 25C, 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.

Reddy, Michael M.; Leenheer, Jerry

2011-01-01

40

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)

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 25C 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.

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

2012-12-01

41

Elastic constants of calcite  

USGS Publications Warehouse

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

Peselnick, L.; Robie, R.A.

1962-01-01

42

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

NASA Astrophysics Data System (ADS)

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

Lian, Zhirui

43

Crystallization of pumpkin seed globulin: growth and dissolution kinetics  

NASA Astrophysics Data System (ADS)

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.

Malkin, Alexander J.; McPherson, Alexander

1993-10-01

44

Lipid composition of high-melting seed crystals formed during cocoa butter solidification  

Microsoft Academic Search

High-melting seed crystals which form during the early stages of cocoa butter solidification possess a lipid composition different\\u000a than the cocoa butter from which the seed crystals were grown. Significantly large quantities of glycolipids, 11.1%, and phospholipids,\\u000a 6.68.1%, were found in the high-melting seed crystals along with a dramatic decrease in the simple lipid class. The fatty\\u000a acids comprising the

Thomas R. Davis; Paul S. Dimick

1989-01-01

45

Stray grain formation in the seed region of single-crystal turbine blades  

Microsoft Academic Search

Seed crystals are frequently used to provide an off-axial ?001? crystallographic orientation to investment cast single-crystal,\\u000a nickel-based superalloy turbine blades. However, stray grain defects can form during the melt-back of the seed crystal, requiring\\u000a the use of a helical grain selector between the seed and the blade to remove them. Using meso-scale numerical simulations,\\u000a the formation mechanisms of these stray

X. L. Yang; P. D. Lee; N. DSouza

2005-01-01

46

Stray grain formation in the seed region of single-crystal turbine blades  

Microsoft Academic Search

Seed crystals are frequently used to provide an off-axial crystallographic orientation to investment cast single-crystal, nickel-based superalloy turbine blades. However, stray grain defects can form during the melt-back of the seed crystal, requiring the use of a helical grain selector between the seed and the blade to remove them. Using meso-scale numerical simulations, the formation mechanisms of these stray grain

X. L. Yang; P. D. Lee; N. D'Souza

2005-01-01

47

The role of silicate surfaces on calcite precipitation kinetics  

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

48

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

49

Zinc isotope fractionation during adsorption on calcite  

NASA Astrophysics Data System (ADS)

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] Marchal 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.

Dong, S.; Wasylenki, L. E.

2013-12-01

50

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

DOEpatents

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.

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

1998-01-01

51

Ammonothermal growth of GaN on a self-nucleated GaN seed crystal  

NASA Astrophysics Data System (ADS)

We performed ammonothermal synthesis of a self-nucleated GaN seed and grew crystalline GaN on the seed in the presence of an NH4F-based mineralizer. Our results suggest that spontaneously nucleated, high-quality GaN crystals can be obtained by recrystallization of polycrystalline hydride vapor phase epitaxy (HVPE) GaN under acidic ammonothermal conditions. We achieved average growth speeds of up to 410 and 465 ?m/day on the c- and m-directions, respectively, after four consecutive crystal growths of GaN on a self-nucleated seed. GaN crystals grown on an HVPE seed and on a self-nucleated seed had comparable crystal quality, judged from room-temperature photoluminescence measurements.

Bao, Quanxi; Saito, Makoto; Hazu, Kouji; Kagamitani, Yuji; Kurimoto, Kouhei; Tomida, Daisuke; Qiao, Kun; Ishiguro, Tohru; Yokoyama, Chiaki; Chichibu, Shigefusa F.

2014-10-01

52

Effect of seed loading and cooling rate on crystal size and shape distributions in protein crystallization - A study using morphological population balance simulation  

Microsoft Academic Search

A morphological population balance model is applied to crystallization of hen-egg white lysozyme for investigation of the effect of seed loading and cooling rate on supersaturation, and crystal size and shape distributions. Growth rates of individual faces and final crystal size and shape distributions were examined under varied seeding and cooling conditions. It was found that for growth only crystallization,

Jing J. Liu; Cai Y. Ma; Yang D. Hu; Xue Z. Wang

2010-01-01

53

A model-based nucleation study of the combined effect of seed properties and cooling rate in cooling crystallization  

Microsoft Academic Search

Crystallization is a widely used unit operation for the production of pharmaceuticals, fertilizers, and fine chemicals. A commonly used crystallization operational objective is to produce large crystals under minimum nucleation rates. For cooling crystallization there are two key methods for minimizing nucleation, programmed cooling and seeding. In this paper, we evaluate the cooling and seeding methods through the detailed modeling

D. J. Widenski; A. Abbas; J. A. Romagnoli

2011-01-01

54

Tetravalent uranium in calcite  

PubMed

X-ray absorption spectroscopy and x-ray fluorescence microprobe studies of 35-million-year-old calcite from a Mississippi Valley-type zinc ore deposit indicate substitution of tetravalent uranium for divalent calcium. Thus, tetravalent uranium has a stable location in calcite deposited under reducing conditions. This result validates uranium-series dating methods (including uranium/lead dating) for ancient calcite and shows that calcite provides a sink for uranium in deep groundwater aquifers and anoxic lacustrine and marine basins. PMID:9703507

Sturchio; Antonio; Soderholm; Sutton; Brannon

1998-08-14

55

Tetravalent uranium in calcite.  

SciTech Connect

X-ray absorption spectroscopy and x-ray fluorescence microprobe studies of 35-million-year-old calcite from a Mississippi Valley-type zinc ore deposit indicate substitution of tetravalent uranium for divalent calcium. Thus, tetravalent uranium has a stable location in calcite deposited under reducing conditions. This result validates uranium-series dating methods (including uranium/lead dating) for ancient calcite and shows that calcite provides a sink for uranium in deep groundwater aquifers and anoxic lacustrine and marine basins.

Sturchio, N. C.; Antonio, M. R.; Soderholm, L.; Sutton, S. R.; Brannon, J. C.; Univ. of Chicago; Washington Univ.

1998-08-14

56

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

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.

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

2000-01-01

57

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

NASA Technical Reports Server (NTRS)

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.

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

1998-01-01

58

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

DOEpatents

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.

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

1998-07-07

59

Calcite precipitation induced by polyurethane-immobilized Bacillus pasteurii.  

PubMed

Polyurethane (PU) foam was used to immobilize the whole cell of Bacillus pasteurii. The immobilized cells exhibited the rates of calcite precipitation and ammonia production as high as those of the free cells. Scanning electron micrographs identified the cells embedded in calcite crystals throughout PU matrices. Calcite in PU showed little effect on the elastic modulus and tensile strength of the polymer, but increased the compressive strengths of concrete cubes, whose cracks were remediated with PU-immobilized cells. These observations led us to believe that the calcite might remain as a form of precipitation, not as a bonding material within the matrices. PMID:11240198

Bang, S S.; Galinat, J K.; Ramakrishnan, V

2001-03-01

60

Dislocation Creep in Magnesium Calcite  

Microsoft Academic Search

To investigate the effect of dissolved Mg on plastic deformation of calcite, we performed triaxial deformation experiments on synthetic calcite with varying amount of Mg content. Mixtures of powders of calcite and dolomite were isostatically hot pressed (HIP) at 850 C and 300 MPa confining pressure for different intervals (2 to 20hrs) resulting in homogeneous aggregates of high-magnesium calcite; Mg

L. Xu; X. Xiao; B. J. Evans

2003-01-01

61

Framboidal Vaterite and its Transformation to Calcite  

Microsoft Academic Search

Vaterite, the most soluble of the three anhydrous calcium carbonate polymorphs, is observed to form in laboratory experiments performed at high degrees of supersaturation. Under standard condition it rapidly transforms into calcite and (or) aragonite. Experimental studies on vaterite are generally based on bubbling carbon dioxide through a calcium carbonate solution. The morphology of the crystals formed is often described

G. Nehrke; P. van Cappellen; C. H. van der Wijden

2003-01-01

62

Framboidal Vaterite and its Transformation to Calcite  

NASA Astrophysics Data System (ADS)

Vaterite, the most soluble of the three anhydrous calcium carbonate polymorphs, is observed to form in laboratory experiments performed at high degrees of supersaturation. Under standard condition it rapidly transforms into calcite and (or) aragonite. Experimental studies on vaterite are generally based on bubbling carbon dioxide through a calcium carbonate solution. The morphology of the crystals formed is often described to be "of some spherical shape", with a typical diameter of about 5m. A detailed investigation of the morphology by means of a high resolution scanning electron microscope (SFEG-SEM) revealed that these spheres in turn are build up of smaller spherical particles with diameters typically 100 nm. Here we propose the following mechanism for the formation of these "framboidal" structures. Nucleation of the first particles occurs on the carbon dioxide to solution interface of the bubble. The fast growth of the individual crystals leads to a depletion in solution around the crystal, which stops crystal growth at a size of about 100 nm. The collapsing gas bubble concentrates the particles within its former volume. Additional evidence for such a mechanism comes from the observation that terminating the experiment after formation of the first particles does not result in any "framboidal" aggregates. Using CO2 bubbling sometimes results in a vaterite powder containing additional calcite. A pure vaterite powder and a powder containing calcite were compared to show different transformation pathways. The morphology of the solids is identical, i.e. the calcite present is not visible under the SFEG-SEM. Calcite formation is observed immediately after a pure vaterite is added to water. Synchronous nucleation at many different sites was observed. The observation that crystal growth was not effected by changes in stirring speed confirms that diffusion did not limit crystal growth. On the hand the powder initially already containing calcite transforms by growth of a few bigger sized crystals. The impact of differences in stirring speed on the transformation rate can be explained by diffusion limited growth of a restricted number of bigger crystals, i.e. less nucleation sites available. Due to Oswald Ripening smaller crystals will eventually disappear and the final morphology of both solids will look similar. However, the different kinetics be explained only by following the change in morphology during the complete transformation process. All evidence of different transformation pathways gets lost as the morphology of the solids before and after transformation is nearly identical.

Nehrke, G.; van Cappellen, P.; van der Wijden, C. H.

2003-12-01

63

InGaAs single crystal using a GaAs seed grown with the vertical gradient freeze technique  

NASA Astrophysics Data System (ADS)

We have succeeded in growing the InGaAs single crystal using a GaAs seed with the vertical gradient freeze technique (VGF) with good reproducibility. The orientation of the GaAs seed is (0 0 1). The boundary conditions between the GaAs seed and the InGaAs VGF crystal, the shape of the solid-liquid interface during crystal growth, and the growth mode of the crystal have been studied as basic conditions for the single crystal growth. We found that (1) The polycrystallinity due to the lattice mismatch between the GaAs seed and the InGaAs VGF crystal can be suppressed when the composition difference ? x between the GaAs seed and the InGaAs crystal is less than 0.05. (2) It is possible to make the solid-liquid interface convex toward the melt by reducing the temperature gradient of the growth zone, which prevents other grains occurring near the crucible wall from propagating to the crystal center region. (3) A normal freezing growth mode can be attained by reducing the lowering rate of the furnace temperature, which prevents compositionally abnormal regions from occurring during crystal growth. The InGaAs crystal obtained is 15 mm long and consists of a single crystal region. The diameter of the growth region is 15 mm, which is the same as that of the GaAs seed. The maximum InAs composition is 0.34

Nishijima, Yoshito; Nakajima, Kazuo; Otsubo, Koji; Ishikawa, Hiroshi

1999-03-01

64

Crystal structure control in Au-free self-seeded InSb wire growth.  

PubMed

In this work we demonstrate experimentally the dependence of InSb crystal structure on the ratio of Sb to In atoms at the growth front. Epitaxial InSb wires are grown by a self-seeded particle assisted growth technique on several different III-V substrates. Detailed investigations of growth parameters and post-growth energy dispersive x-ray spectroscopy indicate that the seed particles initially consist of In and incorporate up to 20at.% Sb during growth. By applying this technique we demonstrate the formation of zinc-blende, 4H and wurtzite structure in the InSb wires (identified by transmission electron microscopy and synchrotron x-ray diffraction), and correlate this sequential change in crystal structure to the increasing Sb/In ratio at the particle-wire interface. The low ionicity of InSb and the large diameter of the wire structures studied in this work are entirely outside the parameters for which polytype formation is predicted by current models of particle seeded wire growth, suggesting that the V/III ratio at the interface determines crystal structure in a manner well beyond current understanding. These results therefore provide important insight into the relationship between the particle composition and the crystal structure, and demonstrate the potential to selectively tune the crystal structure in other III-V compound materials as well. PMID:21346304

Mandl, Bernhard; Dick, Kimberly A; Kriegner, Dominik; Keplinger, Mario; Bauer, Gnther; Stangl, Julian; Deppert, Knut

2011-04-01

65

Microbial precipitation of pedogenic calcite  

Microsoft Academic Search

Pedogenic calcite in desert soils has become increasingly important as an indicator of paleoclimate, landscape stability, and landscape age. This study indicates that calcic and petrocalcic horizons in desert soils are not simply the result of inorganic precipitation of calcite. Soil microorganisms were found to be involved in calcite precipitation in a typical desert soil near Las Cruces, New Mexico.

H. Curtis Monger; LeRoy A. Daugherty; William C. Lindemann; Craig M. Liddell

1991-01-01

66

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

NASA Astrophysics Data System (ADS)

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

Sadhasivam, S.; Rajesh, Narayana Perumal

2014-09-01

67

Microbial precipitation of pedogenic calcite  

SciTech Connect

Pedogenic calcite in desert soils has become increasingly important as an indicator of paleoclimate, landscape stability, and landscape age. This study indicates that calcic and petrocalcic horizons in desert soils are not simply the result of inorganic precipitation of calcite. Soil microorganisms were found to be involved in calcite precipitation in a typical desert soil near Las Cruces, New Mexico. Fossilized remains of calcified fungal hyphae and Microcodium structures are abundant in the petrocalcic horizon. Soil bacteria and fungi precipitated calcite when cultured on a Ca-rich medium. In an experiment where soil columns were irrigated on a Ca-rich solutions, calcite formed in soils containing soil microorganisms, but no calcite formed in sterile soils. Thus, biomineralization of calcite by soil microorganisms appears to be an important mechanism of unknown magnitude.

Monger, H.C.; Daugherty, L.A.; Lindemann, W.C.; Liddell, C.M. (New Mexico State Univ., Las Cruces (United States))

1991-10-01

68

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

PubMed

The cupin superfamily of proteins includes the 7S and 11S seed storage proteins. Many members of this family of proteins are known allergens. In this study, the Korean pine (Pinus koraiensis) vicilin-type 7S seed storage protein was isolated from defatted pine-nut extract and purified by sequential gel-filtration and anion-exchange chromatography. Well diffracting single crystals were obtained by the vapor-diffusion method in hanging drops. The crystals belong to the primitive cubic space group P2(1)3, with unit-cell parameters a = b = c = 148.174 A. Two vicilin molecules were present in the asymmetric unit and the Matthews coefficient was determined to be 2.90 A(3) Da(-1), with a corresponding solvent content of approximately 58%. A molecular-replacement structural solution has been obtained using the program Phaser. Refinement of the structure is currently under way. PMID:18084088

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

2007-12-01

69

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

PubMed Central

A protein with chitinase activity has been isolated and purified from tamarind (Tamarindus indica) seeds. N-terminal amino-acid sequence analysis of this protein confirmed it to be an ?34?kDa endochitinase which belongs to the acidic class III chitinase family. The protein was crystallized by the vapour-diffusion method using PEG 4000. The crystals belonged to the tetragonal space group P41, with two molecules per asymmetric unit. Diffraction data were collected to a resolution of 2.6?. PMID:19342775

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

2009-01-01

70

Enhanced crystallization of amorphous silicon thin films by nano-crystallite seeding  

NASA Astrophysics Data System (ADS)

Polycrystalline silicon (poly-Si) has become popular in recent years as a candidate for low cost, high efficiency thin film solar cells. The possibility to combine the stability against light degradation and electronic properties approaching melt-grown, wafer-based crystallline silicon, with the cost advantage of Silicon thin films is highly attractive. To fully realize this goal, efforts have been focused on maximizing grain size while reducing the thermal input involved in a critical ``annealing'' step. Of the variety of processes involved in this effort, studies have shown that poly-Si films obtained from solid-phase-crystallization (SPC) of hydrogenated amorphous silicon (a-Si:H), grown from non-thermal plasma-enhanced chemical vapor deposition (PECVD), exhibit the potential to achieve the highest quality grain structures. However, reproducible control of grain size has proven difficult, with larger grains typically requiring longer annealing times. In this work, a novel technique is demonstrated for more effectively controlling the final grain structure of SPC-processed films while simultaneously reducing annealing times. The process utilized involves SPC of a-Si:H thin films containing embedded nanocrystallites, intended to serve as predetermined grain-growth sites, or grain-growth ``seeds'', during the annealing process. Films were produced by PECVD with a system in which two plasmas were operated to produce crystallites and amorphous films separately. This approach allows crystallite synthesis conditions to be tuned independently from a-Si:H film synthesis conditions, providing a large parameter space available for process optimization, including the effects of particle size, shape, quantity, and location within the film. The work contained here-in outlines the effects of select parameters on the both grain size control and thermal budget. Reproducible control of both grain size and crystallization rate were demonstrated through varying initial seed crystal concentrations. Significant reductions in annealing times were demonstrated to occur in seeded films relative to unseeded films, with both seed crystal concentration and seed crystal geometry demonstrating significant effects on crystallization rate. Furthermore, the development of this technique has resulted in potentially new insights on the material system involved, with the observation of a potentially unique phase-transformation mechanism.

Trask, Jason

71

Crystallochemical characterization of calcium oxalate crystals isolated from seed coats of Phaseolus vulgaris and leaves of Vitis vinifera.  

PubMed

Calcium oxalate crystals are a major biomineralization product in higher plants. Their biological function and use are not well understood. In this work, we focus on the isolation and crystallochemical characterization of calcium oxalate crystals from seed coats of Phaseolus vulgaris (prisms) and leaves of Vitis vinifera (raphides and druses) using ultrastructural methods. A proposal based on crystal growth theory was used for explaining the existence of different morphologies shown by these crystals grown inside specialized cells in plants. PMID:12749080

Juregui-Ziga, David; Reyes-Grajeda, Juan Pablo; Seplveda-Snchez, Jos David; Whitaker, John R; Moreno, Abel

2003-03-01

72

Controlled growth of vertically aligned ZnO nanowires with different crystal orientation of the ZnO seed layer  

Microsoft Academic Search

A novel synthesis and growth method achieving vertically aligned zinc oxide (ZnO) nanowires on a silicon dioxide (SiO2) coated silicon (Si) substrate is demonstrated. The growth direction of the ZnO nanowires is determined by the crystal structure of the ZnO seed layer, which is formed by the oxidation of a DC-sputtered Zn film. The [002] crystal direction of the seed

S N Cha; B G Song; J E Jang; J E Jung; I T Han; J H Ha; J P Hong; D J Kang; J M Kim

2008-01-01

73

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

DOEpatents

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.

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

1997-01-01

74

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

DOEpatents

A method of fabricating bulk superconducting material is disclosed including RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} comprising heating compressed powder oxides and/or carbonates of R and Ba and Cu present in mole ratios to form RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} in physical contact with an oxide single crystal seed to a temperature sufficient to form a liquid phase in the RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} while maintaining the single crystal seed solid to grow the superconducting material and thereafter cooling to provide a material including RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}. R is a rare earth or Y or La and the single crystal seed has a lattice mismatch with RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} of less than about 2% at the growth temperature. The starting material may be such that the final product contains a minor amount of R{sub 2}BaCuO{sub 5}.

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

1997-03-18

75

Effect of seed orientation on the growth of TGS crystals with large (0 1 0) facets needed for detector applications  

NASA Astrophysics Data System (ADS)

It is advantageous to grow crystals of triglycine sulphate (TGS) with a large area in the plane perpendicular to the polar axis (i.e. the (0 1 0) plane), for applications in large-area infrared detectors and laser-energy meters. Growing TGS crystals with such a morphology, using a point seed, has been a difficult task because of a low growth rate along the c-direction. To overcome this problem a cylindrical seed of large dimension along the c-axis is commonly used. This paper reports the growth of TGS crystals by the platform technique, using seeds which need not be long along the c-axis. Crystals were grown from aqueous solution by placing seeds of size 555 mm 3 in different orientations on the platform. The variation of growth rates of various habit facets with different orientations of seeds was determined. An optimum seed orientation was found such that the platform technique permits one to grow TGS crystals from which large-area (0 1 0) plates can be cut. The grown crystals were characterised by various techniques. A laser-energy meter was designed, fabricated, and tested.

Satapathy, S.; Sharma, S. K.; Karnal, A. K.; Wadhawan, V. K.

2002-04-01

76

Primary magmatic calcite reveals origin from crustal carbonate  

NASA Astrophysics Data System (ADS)

We have investigated lava flows representative of the whole eruptive history of the Colli Albani ultrapotassic volcanic district (Central Italy). One of the most intriguing features concerning some of these lava flows is the occurrence of primary, magmatic calcite in the groundmass. The primary, magmatic nature of calcite has been inferred by microtextural investigations showing that it typically occurs i) interstitially, associated with clinopyroxene, nepheline and phlogopite, ii) in spherical ocelli, associated with nepheline, fluorite and tangentially arranged clinopyroxene, and iii) in corona-like reaction zones around K-feldspar xenocrysts. These microtextural features distinctly indicate that calcite crystallized from a carbonate melt in a partially molten groundmass, implying that the temperature of the system was above the solidus of the hosted lava flow (> 850 C). Geochemical features of calcite crystals (i.e., stable isotope values and trace element patterns) corroborate their primary nature and give insights into the origin of the parental carbonate melt. The trace element patterns testify to a high-temperature crystallization process (not hydrothermal) involving a carbonate melt coexisting with a silicate melt. The high ?18O (around 27 SMOW) and wide ?13C (- 18 to + 5 PDB) values measured in the calcites preclude a mantle origin, but are consistent with an origin in the crust. In this framework, the crystallization of calcite can be linked to the interaction between magmas and carbonate-bearing wall rocks and, in particular, to the entrapment of solid and/or molten carbonate in the silicate magma. The stability of carbonate melt at low pressure and the consequent crystallization of calcite in the lava flow groundmass are ensured by the documented, high activity of fluorine in the studied system and by the limited ability of silicate and carbonate melts to mix at syn-eruptive time scales.

Gozzi, Fernando; Gaeta, Mario; Freda, Carmela; Mollo, Silvio; Di Rocco, Tommaso; Marra, Fabrizio; Dallai, Luigi; Pack, Andreas

2014-03-01

77

Growth of AlN bulk crystals on SiC seeds: Chemical analysis and crystal properties  

NASA Astrophysics Data System (ADS)

AlN single crystals are grown by physical vapor transport (PVT) in sintered TaC crucibles in the presence of SiC, i.e. by seeding on 6H-SiC or by adding SiC to the AlN source material. Different growth conditions, i.e. growth temperatures T=1900-2050 C and off-orientation angles in respect to [0001] ?=0-42, are applied in order to investigate to which extent the incorporation of Si and/or C can be controlled during the PVT growth. Chemical analysis is performed by energy-dispersive X-ray analysis (EDX), secondary ion mass spectrometry (SIMS), and Rutherford backscattering spectroscopy (RBS). The grown crystals are significantly contaminated with Si and C in the range of several atomic percents, but they do not represent pseudo-binary AlN-SiC solid solutions. Samples cut from these crystals are probed by Raman micro-spectroscopy, optical absorption, cathodoluminescence (CL), and near band-gap photoluminescence (PL) in order to evaluate the crystal properties. All crystals exhibit phonon bands at the positions of AlN phonon energies, and a low-temperature band-gap exceeding 5.8 eV, which is only slightly lower than the band-gap of pure AlN. On the other hand, the samples show very different optical properties below the band-gap, including coloration. As the changes in optical properties do not correlate to chemical analysis, we suggest that self-compensation of silicon and carbon as well as formation of intrinsic defects lead to a complex compensation scenario in the samples. The grown crystals are thus to be considered as highly compensated, Si/C co-doped AlN.

Bickermann, Matthias; Filip, Octavian; Epelbaum, Boris M.; Heimann, Paul; Feneberg, Martin; Neuschl, Benjamin; Thonke, Klaus; Wedler, Elke; Winnacker, Albrecht

2012-01-01

78

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)

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.

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

2014-06-01

79

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

NASA Astrophysics Data System (ADS)

In this study, we demonstrate a key function of extracellular matrix proteins (ECMPs) on seed crystals, which are isolated from calcified endoskeletons of soft coral and contain only CaCO 3 without any living cells. This is the first report that an ECMP protein extracted from a marine organism could potentially influence in modifying the surface of a substrate for designing materials via crystallization. We previously studied with the ECMPs from a different type of soft coral ( Sinularia polydactyla) without introducing any seed crystals in the process , which showed different results. Thus, crystallization on the seed in the presence of ECMPs of present species is an important first step toward linking function to individual proteins from soft coral. For understanding this interesting phenomenon, in vitro crystallization was initiated in a supersaturated solution on seed particles of calcite (1 0 4) with and without ECMPs. No change in the crystal growth shape occurred without ECMPs present during the crystallization process. However, with ECMPs, the morphology and phase of the crystals in the crystallization process changed dramatically. Upon completion of crystallization with ECMPs, an attractive crystal morphology was found. Scanning electron microscopy (SEM) was utilized to observe the crystal morphologies on the seeds surface. The mineral phases of crystals nucleated by ECMPs on the seeds surface were examined by Raman spectroscopy. Although 50 mM Mg 2+ is influential in making aragonite in the crystallization process, the ECMPs significantly made calcite crystals even when 50 mM Mg 2+ was present in the process. Crystallization with the ECMP additive seems to be a technically attractive strategy to generate assembled micro crystals that could be used in crystals growth and design in the Pharmaceutical and biotechnology industries.

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

2011-06-01

80

Sulfated Macromolecules as Templates for Calcite Nucleation and Growth  

NASA Astrophysics Data System (ADS)

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.

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

2003-12-01

81

Calcite in Lesquerella ovalifolia Trichomes.  

PubMed

By chemical analysis, trichomes of Lesquerella ovalifolia Rydb. have been shown to contain a high percentage of calcium carbonate. X-ray diffraction patterns showed that it was in the form of calcite. The calcite was inside the trichomes, and its depositional pattern conformed to the shape of the trichomes. A small amount of opal was present in the trichomes. PMID:17815828

Lanning, F C

1961-02-10

82

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

NASA Astrophysics Data System (ADS)

Speleothems are one of the most intensively explored continental archives for palaeoclimate variability. The parameters, however, that control speleothem petrography and its changes with time and space, specifically calcite crystal morphology and carbonate mineralogy, are still poorly understood. In order to shed light on processes and their products, precipitation experiments of recent carbonate crystals on watch glasses and glass plates were performed in seven selected caves. Drip water sites were analysed for their fluid Mg/Ca molar ratio, pH, degree of saturation for calcite and aragonite and drip rates. Corresponding precipitates were analysed with respect to their mineralogy, calcite crystal morphology and Mg/Ca molar ratio of calcite. The following results are found: High fluid Mg/Ca ratios are found only for caves situated in dolostone, thus the hostrock lithology indirectly controls the carbonate mineralogy and calcite crystal morphology of speleothems. The precipitation of aragonite in place of calcite occurred only in dolostone caves and is bound to very specific conditions. These are: high fluid Mg/Ca ratios (?0.5), high fluid pH (>8.2) and low fluid saturation indices for calcite (<0.8). These specific conditions are induced by slow drip rates of <0.2 ml/min as often under more arid conditions, causing the precipitation of calcite/aragonite prior to reaching the stalagmite top. Due to this, fluid chemistry is altered, which in turn leads to changes in carbonate mineralogy and geochemistry on the stalagmite top. Calcite growth is inhibited at high fluid Mg/Ca ratios and hence, aragonite precipitation is kinetically stabilised. An increase of the drip water Mg/Ca ratio leads to an increased incorporation of Mg2+ into the calcite crystal lattice and thus, to a change in calcite crystal morphology. Four distinctive changes occur with increasing Mg2+ incorporation: (i) development of new forms (steeper rhombohedra and base pinacoid) at the edges and corners of the crystal seed, (ii) crystal habit tend to elongate along [0 0 1] due to slower growth of faces with high Mg2+ densities, (iii) reconstitution of crystal faces with low Mg2+ densities, and (iv) occurrence of calcite crystals with bended faces and edges due to very high Mg2+ (Mg/Ca ratios of 0.009-0.051) incorporation. Growth rates and possibly also organic compounds, however, may also affect the morphology of calcite crystals. Based on the data shown here, the relation of Mg2+ incorporation and the resulting changes in calcite crystal morphologies as well as the conditions of aragonite precipitation are now clearly better understood. Further work should aim at linking the calcite crystal morphology of watch glass precipitates with calcite crystal fabrics in speleothems in order to exploit the petrographic archive of speleothem deposits.

Riechelmann, Sylvia; Schrder-Ritzrau, Andrea; Wassenburg, Jasper A.; Schreuer, Jrgen; Richter, Detlev K.; Riechelmann, Dana F. C.; Terente, Mihai; Constantin, Silviu; Mangini, Augusto; Immenhauser, Adrian

2014-11-01

83

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

SciTech Connect

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}.

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

2012-06-28

84

Crystal Structure of Korean Pine ( Pinus koraiensis ) 7S Seed Storage Protein with Copper Ligands.  

PubMed

The prevalence of food allergy has increased in recent years, and Korean pine vicilin is a potential food allergen. We have previously reported the crystallization of Korean pine vicilin purified from raw pine nut. Here we report the isolation of vicilin mRNA and the crystal structure of Korean pine vicilin at 2.40 resolution. The overall structure of pine nut vicilin is similar to the structures of other 7S seed storage proteins and consists of an N-terminal domain and a C-terminal domain. Each assumes a cupin fold, and they are symmetrically related about a pseudodyad axis. Three vicilin molecules form a doughnut-shaped trimer through head-to-tail association. Structure characterization of Korean pine nut vicilin unexpectedly showed that, in its native trimeric state, the vicilin has three copper ligands. Sequence alignments suggested that the copper-coordinating residues were conserved in winter squash, sesame, tomato, and several tree nuts, while they were not conserved in a number of legumes, including peanut and soybean. Additional studies are needed to assess whether the copper-coordinating property of vicilins has a biological function in the relevant plants. The nutritional value of this copper-coordinating protein in tree nuts and other edible seeds may be worth further investigations. PMID:24328105

Jin, Tengchuan; Wang, Yang; Chen, Yu-Wei; Fu, Tong-Jen; Kothary, Mahendra H; McHugh, Tara H; Zhang, Yuzhu

2014-01-01

85

The influence of P CO 2 on the partitioning of magnesium in calcite overgrowths precipitated from artificial seawater at 25 and 1 atm total pressure  

NASA Astrophysics Data System (ADS)

The influence of carbon dioxide partial pressure (P CO 2) on the composition of magnesian calcite overgrowths precipitated from artificial seawater at 25 C on synthetic, rhombohedral calcite seeds was investigated using a chemo-stat precipitation technique. Powder X-ray diffraction (XRD) analyses of the overgrowths indicate that the amount of MgCO 3 incorporated during the precipitation is independent of the p co 2 over four orders of magnitude (10 -0.5 to 10 -4.6 atm). The magnesium content of the overgrowths estimated from mass balance calculations of the carbonate alkalinity of the reacting solutions (? Ac) and flame atomic absorption spectrophotometric (AA) analyses of the reacted solids yield similar results. Values determined by the latter method are compromised by calculation errors arising from gas phase disequilibrium when the alkalinity is computed from the steady state pH and P CO 2, of the gas phase. The concentration of sodium in the overgrowths, however, appears to correlate with variations in P CO 2. The lack of correlation between magnesium partitioning in calcite overgrowths and P CO 2 observed in this study contrasts with results obtained by previous investigators but does not preclude that the composition of calcite cements could be affected by variations in growth mechanism induced by changes in solution variables or the nature of the substrate. Based on the results of this study and recent laboratory and field observations, we propose that a change in growth mechanism and differential partitioning of magnesium on nonequivalent faces of a growing calcite crystal in seawater could explain some of the compositional variability of modern, marine calcite cements. In view of these latter considerations, we feel that it is premature to speculate on conditions that led to cyclic secular variations in the composition and mineralogy of marine carbonate cements precipitated during the Phanerozoic.

Hartley, George; Mucci, Alfonso

1996-01-01

86

Amorphous Calcium Carbonate Transforms into Calcite during Sea Urchin Larval Spicule Growth  

Microsoft Academic Search

Sea urchin larvae form an endoskeleton composed of a pair of spicules. For more than a century it has been stated that each spicule comprises a single crystal of the CaCO3 mineral, calcite. We show that an additional mineral phase, amorphous calcium carbonate, is present in the sea urchin larval spicule, and that this inherently unstable mineral transforms into calcite

Elia Beniash; Joanna Aizenberg; Lia Addadi; Stephen Weiner

1997-01-01

87

Strontium Incorporation Into Calcite Generated by Bacterial Ureolysis  

NASA Astrophysics Data System (ADS)

Strontium incorporation into calcite generated by bacterial ureolytic activity was investigated as part of a larger effort to evaluate the use of in situ urea hydrolysis for accelerating co-precipitation of trace metals and radionuclides in contaminated aquifers. 90Sr, a uranium fission product with a half-life of 29 years, is a significant subsurface contaminant at several Department of Energy facilities and could be immobilized using this remediation strategy. Experiments were conducted in a medium designed to simulate the groundwater of the Snake River Plain Aquifer in eastern Idaho, amended with strontium. Initially the solution was undersaturated with respect to calcite. As a model ureolytic organism, we used Bacillus pasteurii, a well-characterized bacterium known for high urease activity and previously shown to induce calcite precipitation in urea-amended medium. To gain information on the effect of the bacterial surfaces, we also looked at precipitation in the presence of a bacterial species that did not hydrolyze urea, as well as in the absence of bacteria. In the absence of bacterial ureolysis, carbonate precipitation was induced by addition of ammonium carbonate. All products were identified as calcite by X-ray diffraction. Strontium uptake was observed in all cases, but was greatest in the system including bacterial ureolysis. Sputter depth element profiling by time-of-flight secondary ion mass spectrometry (TOF-SIMS) confirmed this finding, showing highest Sr:Ca ratios in the bacterially generated calcite throughout the depth (~350 nm) investigated. Environmental Scanning Electron Microscopy (ESEM) of the solids revealed regular crystals containing the outlines of embedded or entombed bacterial cells, suggesting that calcite precipitated directly on the cell surfaces when present. Analysis by X-ray Absorption Near Edge Spectroscopy (XANES) indicated that in both the biotically and abiotically generated calcites the Sr was incorporated into the calcite lattice structure, rather than forming strontium carbonate. These findings are encouraging with respect to long term containment and stabilization of strontium by the proposed remediation strategy.

Fujita, Y.; Ingram, J. A.; Cortez, M. M.; Redden, G. D.; Smith, R. W.

2002-12-01

88

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

PubMed Central

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 P212121. The crystals diffracted to 2.8? resolution at 103?K. PMID:22139159

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

2011-01-01

89

Influence of Bacillus subtilis Cell Walls and EDTA on Calcite  

E-print Network

Influence of Bacillus subtilis Cell Walls and EDTA on Calcite Dissolution Rates and Crystal Surface and the Gram-positive cell walls of Bacillus subtilis on the dissolution rates and development of morphological that the presence of metabolically inactive B. subtilis does not affect the dissolution rates significantly

Long, Bernard

90

Controlled growth of vertically aligned ZnO nanowires with different crystal orientation of the ZnO seed layer  

NASA Astrophysics Data System (ADS)

A novel synthesis and growth method achieving vertically aligned zinc oxide (ZnO) nanowires on a silicon dioxide (SiO2) coated silicon (Si) substrate is demonstrated. The growth direction of the ZnO nanowires is determined by the crystal structure of the ZnO seed layer, which is formed by the oxidation of a DC-sputtered Zn film. The [002] crystal direction of the seed layer is dominant under optimized thickness of the Zn film and thermal treatment. Vertically aligned ZnO nanowires on SiO2 coated Si substrate are realized from the appropriately thick oxidized Zn seed layer by a vapor-solid growth mechanism by catalyst-free thermal chemical vapor deposition (CVD). These experimental results raise the possibility of using the nanowires as functional blocks for high-density integration systems and/or photonic applications.

Cha, S. N.; Song, B. G.; Jang, J. E.; Jung, J. E.; Han, I. T.; Ha, J. H.; Hong, J. P.; Kang, D. J.; Kim, J. M.

2008-06-01

91

Biotic Control of Skeletal Growth by Scleractinian Corals in Aragonite-Calcite Seas  

PubMed Central

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

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

2014-01-01

92

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

93

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

94

Sea urchin tooth mineralization: Calcite present early in the aboral plumula  

PubMed Central

In both vertebrate bone, containing carbonated hydroxyapatite as the mineral phase, and in invertebrate hard tissue comprised of calcium carbonate, a popular view is that the mineral phase develops from a long-lived amorphous precursor which later transforms into crystal form. Important questions linked to this popular view are: When and where is the crystallized material formed, and is amorphous solid added subsequently to the crystalline substrate? Sea urchin teeth, in which the earliest mineral forms within isolated compartments, in a time and position dependent manner, allow direct investigation of the timing of crystallization of the calcite primary plates. Living teeth of the sea urchin Lytechinus variegatus, in their native coelomic fluid, were examined by high-energy synchrotron x-ray diffraction. The diffraction data show that calcite is present in the most aboral portions of the plumula, representing the very earliest stages of mineralization, and that this calcite has the same crystal orientation as in the more mature adoral portions of the same tooth. Raman spectroscopy of the aboral plumula confirms the initial primary plate mineral material is calcite and does not detect amorphous calcium carbonate; in the more mature adoral incisal flange, it does detect a broader calcite peak, consistent with two or more magnesium compositions. We hypothesize that some portion of each syncytial membrane in the plumula provides the information for nucleation of identically oriented calcite crystals that subsequently develop to form the complex geometry of the single crystal sea urchin tooth. PMID:22940703

Stock, Stuart R.; Veis, Arthur; Xiao, Xianghui; Almer, Jonathan D.; Dorvee, Jason R.

2012-01-01

95

Conservation and divergence on plant seed 11S globulins based on crystal structures.  

PubMed

The crystal structures of two pro-11S globulins namely: rapeseed procruciferin and pea prolegumin are presented here. We have extensively compared them with the other known structures of plant seed 11S and 7S globulins. In general, the disordered regions in the crystal structures among the 11S globulins correspond to their five variable regions. Variable region III of procruciferin is relatively short and is in a loop conformation. This region is highly disordered in other pro-11S globulin crystals. Local helical and strand variations also occur across the group despite general structure conservation. We showed how these variations may alter specific physicochemical, functional and physiological properties. Aliphatic hydrophobic residues on the molecular surface correlate well with Tm values of the globulins. We also considered other structural features that were reported to influence thermal stability but no definite conclusion was drawn since each factor has additive or subtractive effect. Comparison between proA3B4 and mature A3B4 revealed an increase in r.m.s.d. values near variable regions II and IV. Both regions are on the IE face. Secondary structure based alignment of 11S and 7S globulins revealed 16 identical residues. Based on proA3B4 sequence, Pro60, Gly128, Phe163, Phe208, Leu213, Leu227, Ile237, Pro382, Val404, Pro425 and Val 466 are involved in trimer formation and stabilization. Gly28, Gly74, Asp135, Gly349 and Gly397 are involved in correct globular folding. PMID:20215054

Tandang-Silvas, Mary Rose G; Fukuda, Takako; Fukuda, Chisato; Prak, Krisna; Cabanos, Cerrone; Kimura, Aiko; Itoh, Takafumi; Mikami, Bunzo; Utsumi, Shigeru; Maruyama, Nobuyuki

2010-07-01

96

Micro-CT observations of the 3D distribution of calcium oxalate crystals in cotyledons during maturation and germination in Lotus miyakojimae seeds.  

PubMed

The cotyledon of legume seeds is a storage organ that provides nutrients for seed germination and seedling growth. The spatial and temporal control of the degradation processes within cotyledons has not been elucidated. Calcium oxalate (CaOx) crystals, a common calcium deposit in plants, have often been reported to be present in legume seeds. In this study, micro-computed tomography (micro-CT) was employed at the SPring-8 facility to examine the three-dimensional distribution of crystals inside cotyledons during seed maturation and germination of Lotus miyakojimae (previously Lotus japonicus accession Miyakojima MG-20). Using this technique, we could detect the outline of the embryo, void spaces in seeds and the cotyledon venation pattern. We found several sites that strongly inhibited X-ray transmission within the cotyledons. Light and polarizing microscopy confirmed that these areas corresponded to CaOx crystals. Three-dimensional observations of dry seeds indicated that the CaOx crystals in the L. miyakojimae cotyledons were distributed along lateral veins; however, their distribution was limited to the abaxial side of the procambium. The CaOx crystals appeared at stage II (seed-filling stage) of seed development, and their number increased in dry seeds. The number of crystals in cotyledons was high during germination, suggesting that CaOx crystals are not degraded for their calcium supply. Evidence for the conservation of CaOx crystals in cotyledons during the L. miyakojimae germination process was also supported by the biochemical measurement of oxalic acid levels. PMID:23220770

Yamauchi, Daisuke; Tamaoki, Daisuke; Hayami, Masato; Takeuchi, Miyuki; Karahara, Ichirou; Sato, Mayuko; Toyooka, Kiminori; Nishioka, Hiroshi; Terada, Yasuko; Uesugi, Kentaro; Takano, Hidekazu; Kagoshima, Yasushi; Mineyuki, Yoshinobu

2013-06-01

97

Calcite formation in soft coral sclerites is determined by a single reactive extracellular protein.  

PubMed

Calcium carbonate exists in two main forms, calcite and aragonite, in the skeletons of marine organisms. The primary mineralogy of marine carbonates has changed over the history of the earth depending on the magnesium/calcium ratio in seawater during the periods of the so-called "calcite and aragonite seas." Organisms that prefer certain mineralogy appear to flourish when their preferred mineralogy is favored by seawater chemistry. However, this rule is not without exceptions. For example, some octocorals produce calcite despite living in an aragonite sea. Here, we address the unresolved question of how organisms such as soft corals are able to form calcitic skeletal elements in an aragonite sea. We show that an extracellular protein called ECMP-67 isolated from soft coral sclerites induces calcite formation in vitro even when the composition of the calcifying solution favors aragonite precipitation. Structural details of both the surface and the interior of single crystals generated upon interaction with ECMP-67 were analyzed with an apertureless-type near-field IR microscope with high spatial resolution. The results show that this protein is the main determining factor for driving the production of calcite instead of aragonite in the biocalcification process and that -OH, secondary structures (e.g. ?-helices and amides), and other necessary chemical groups are distributed over the center of the calcite crystals. Using an atomic force microscope, we also explored how this extracellular protein significantly affects the molecular-scale kinetics of crystal formation. We anticipate that a more thorough investigation of the proteinaceous skeleton content of different calcite-producing marine organisms will reveal similar components that determine the mineralogy of the organisms. These findings have significant implications for future models of the crystal structure of calcite in nature. PMID:21768106

Rahman, M Azizur; Oomori, Tamotsu; Wrheide, Gert

2011-09-01

98

Micro-mechanical model of calcium oxalate monohydrate aggregation in supersaturated solutions: Effect of crystal form and seed concentration  

NASA Astrophysics Data System (ADS)

In this paper we report crystal growth and aggregation behaviour for calcium oxalate monohydrate (COM) in a stirred tank for two differing seed types - rounded and well defined - at various seed loadings. Initially we used our previously developed model [1] to study the growth and aggregation. In this model a dimensionless strength, termed the Mumtaz number, has been formulated, which accounts for the effects of stirring, supersaturation and particle size on the aggregation rate of COM. Subtle differences in growth and aggregation rates were observed between the two populations of crystals; the model was unable to describe this behaviour. These differences were attributed to their different surface characteristics. Growth and aggregation kinetic parameters were also seen to be highly dependent on seed loading. This is attributed to poisoning by an unknown trace impurity, the effect of which is dependent on seed loading. This has led to the development of a new model to account for both surface characteristics and the presence of a trace impurity that adsorbs onto the surface of crystals pinning growth steps. At low seeds loadings, surface coverage by the impurity is higher and so growth rates are reduced. These results are very well described by an extension of the approach of Weaver et al. [2]. We use Liew et al.'s [1] model to represent aggregation by a collision efficiency that depends on a modified Mumtaz number. This model requires the determination of a simple group of parameters that we term the 'aggregation tendency'. The relationship between aggregation tendency and growth rate constant suggests that aggregation is in fact controlled by the growth rate of some high-energy facets not expressed macroscopically. The fact that aggregation tendency increases with surface coverage of impurity further suggests that the presence of impurity gives rise to longer or more numerous linear features along which initial contact between crystals takes place. The combined growth and aggregation models are capable of describing all the experiments reported here for both seed types and over a range of seed loadings.

Pitt, K.; Mitchell, G. P.; Ray, A.; Heywood, B. R.; Hounslow, M. J.

2012-12-01

99

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

PubMed

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

Lpez-Martnez, Juan Carlos; Campra-Madrid, Pablo; Guil-Guerrero, Jos Luis

2004-01-01

100

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

PubMed

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

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

2012-01-01

101

Aragonite shells are more ancient than calcite ones in bivalves: new evidence based on omics.  

PubMed

Two calcium carbonate crystal polymorphs, aragonite and calcite, are the main inorganic components of mollusk shells. Some fossil evidences suggest that aragonite shell is more ancient than calcite shell for the Bivalvia. But, the molecular biology evidence for the above deduction is absent. In this study, we searched for homologs of bivalve aragonite-related and calcite-related shell proteins in the oyster genome, and found that no homologs of calcite-related shell protein but some homologs of aragonite-related shell proteins in the oyster genome. We explained the results as the new evidence to support that aragonite shells are more ancient than calcite shells in bivalves combined the published biogeological and seawater chemistry data. PMID:25063580

Wang, Xiaotong; Li, Li; Zhu, Yabing; Song, Xiaorui; Fang, Xiaodong; Huang, Ronglian; Que, Huayong; Zhang, Guofan

2014-11-01

102

Improvement in microstructure and crystal alignment of ZnO films grown by metalorganic chemical vapor deposition using a seed layer  

Microsoft Academic Search

An epitaxially aligned ZnO nano-seed layer was used to improve the microstructure and crystal alignment in metalorganic chemical vapor deposited ZnO films on Al2O3 (0001) substrates. Comparative investigations were performed on the properties of the ZnO films grown with and without the seed layer. The ZnO film grown directly on the substrate without applying the seed layer shows an irregular,

Jae Young Park; Dong Ju Lee; Byung-Teak Lee; Jong Ha Moon; Sang Sub Kim

2005-01-01

103

Improvement in microstructure and crystal alignment of ZnO films grown by metalorganic chemical vapor deposition using a seed layer  

Microsoft Academic Search

An epitaxially aligned ZnO nano-seed layer was used to improve the microstructure and crystal alignment in metalorganic chemical vapor deposited ZnO films on Al2O3 (0 0 0 1) substrates. Comparative investigations were performed on the properties of the ZnO films grown with and without the seed layer. The ZnO film grown directly on the substrate without applying the seed layer

Jae Young Park; Dong Ju Lee; Byung-Teak Lee; Jong Ha Moon; Sang Sub Kim

2005-01-01

104

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

NASA Astrophysics Data System (ADS)

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.

Vaniman, David T.; Chipera, Steve J.

1996-11-01

105

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

SciTech Connect

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.

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

106

Magnesium stable isotope fractionation in marine biogenic calcite and aragonite  

NASA Astrophysics Data System (ADS)

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 in calcitic corals and sclerosponges agrees with published data for calcitic speleothems with an average ? 26Mg calcite-seawater = -2.6 0.3 that appears to be weakly related to temperature. With one exception ( Vaceletia spp.), aragonitic corals and sclerosponges also display uniform Mg isotope fractionations relative to seawater with ? 26Mg biogenic aragonite-seawater = -0.9 0.2. Magnesium isotopes in high-Mg calcites from red algae, echinoids and perhaps some porcelaneous foraminifera as well as in all low-Mg calcites (perforate foraminifera, coccoliths and brachiopods) display significant biological influences. For planktonic foraminifera, the Mg isotope data is consistent with the fixation of Mg by organic material under equilibrium conditions, but appears to be inconsistent with Mg removal from vacuoles. Our preferred model, however, suggests that planktonic foraminifera synthesize biomolecules that increase the energetic barrier for Mg incorporation. In this model, the need to remove large quantities of Mg from vacuole solutions is avoided. For the high-Mg calcites from echinoids, the precipitation of amorphous calcium carbonate may be responsible for their weaker Mg isotope fractionation. Disregarding superimposed biological effects, it appears that cation light isotope enrichments in CaCO 3 principally result from a chemical kinetic isotope effect, related to the incorporation of cations at kink sites. In this model, the systematics of cation isotope fractionations in CaCO 3 relate to the activation energy required for cation incorporation, which probably reflects the dehydration of the cation and the crystal surface and bond formation at the incorporation site. This kinetic incorporation model predicts (i) no intrinsic dependence on growth rate, unless significant back reaction upon slow growth reduces the isotope fractionation towards that characteristic for equilibrium isotope partitioning (this may be observed for Ca isotopes in calcites), (ii) a small decrease of isotope fractionation with increasing temperature that may be amplified if higher temperatures promote back reaction and (iii) a sensitivity to changes in the activation barrier caused by additives such as anions or biomolecules or by the initial formation of amorphous CaCO 3.

Wombacher, F.; Eisenhauer, A.; Bhm, F.; Gussone, N.; Regenberg, M.; Dullo, W.-Chr.; Rggeberg, A.

2011-10-01

107

Improvement in microstructure and crystal alignment of ZnO films grown by metalorganic chemical vapor deposition using a seed layer  

NASA Astrophysics Data System (ADS)

An epitaxially aligned ZnO nano-seed layer was used to improve the microstructure and crystal alignment in metalorganic chemical vapor deposited ZnO films on Al 2O 3 (0 0 0 1) substrates. Comparative investigations were performed on the properties of the ZnO films grown with and without the seed layer. The ZnO film grown directly on the substrate without applying the seed layer shows an irregular, leaf-like surface morphology with a large surface roughness. Moreover, its crystal alignment is random. In sharp contrast, a fairly smooth surface is observed for the ZnO film grown with the seed layer. In addition, the film shows an epitaxially aligned nature. Our results suggest that the insertion of the nano-seed layer be an effective way to grow well-oriented, smooth ZnO films.

Young Park, Jae; Ju Lee, Dong; Lee, Byung-Teak; Ha Moon, Jong; Kim, Sang Sub

2005-03-01

108

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

NASA Astrophysics Data System (ADS)

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.

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

2013-10-01

109

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

E-print Network

Seeded growth of AlN bulk crystals in m- and c-orientation P. Lu a , R. Collazo a,?, 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

Dietz, Nikolaus

110

InGaAs single crystal with a uniform composition in the growth direction grown on an InGaAs seed using the multicomponent zone growth method  

NASA Astrophysics Data System (ADS)

We succeeded in growing an In xGa 1- xAs single crystal with a uniform composition in the growth direction using the multicomponent zone growth (MCZG) method. An InGaAs crystal, grown on a GaAs seed using the vertical gradient freeze technique (VGF), was used as an InGaAs seed for the MCZG method. We studied the controllability of the InGaAs crystal composition grown using the MCZG method and the growth conditions for the InGaAs MCZG single crystal. Consequently, we found that: (1) It is possible to obtain an InGaAs crystal with a uniform composition in the growth direction by adjusting the cooling rate of the growth zone. (2) An InGaAs MCZG single crystal can be grown on an InGaAs single seed by suppressing the occurrence of fast crystal growth at the beginning of MCZG. The MCZG region obtained was 5 mm long and was a single crystal. The uniform InAs composition region of 0.3 was 3 mm long. The orientation of the crystal was (0 0 1).

Nishijima, Yoshito; Nakajima, Kazuo; Otsubo, Koji; Ishikawa, Hiroshi

2000-01-01

111

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

SciTech Connect

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.

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

1985-01-01

112

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

NASA Astrophysics Data System (ADS)

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 (<40C 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 0.20.02 to 35.82.7 Ma, as well as two older dates of 11710 and 20528 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.

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

2013-12-01

113

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

PubMed Central

A Kunitz-type proteinase inhibitor has been purified from tamarind (Tamarindus indica) seeds. SDSPAGE analysis of a purified sample showed a homogeneous band corresponding to a molecular weight of 21?kDa. The protein was identified as a Kunitz-type proteinase inhibitor based on N-terminal amino-acid sequence analysis. It was crystallized by the vapour-diffusion method using PEG 6000. The crystals belonged to the orthorhombic space group C2221, with unit-cell parameters a = 37.2, b = 77.1, c = 129.1?. Diffraction data were collected toaresolution of 2.7?. Preliminary crystallographic analysis indicated the presence of one proteinase inhibitor molecule in the asymmetric unit, with a solvent content of 44%. PMID:19574654

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

2009-01-01

114

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

PubMed

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?, ? = 74.30, ? = 76.65, ? = 86.88. X-ray diffraction data were collected to a resolution of 2.44? 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

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

2011-04-01

115

High performance low temperature polycrystalline Si thin-film transistors fabricated by silicide seed-induced lateral crystallization  

NASA Astrophysics Data System (ADS)

A novel and simple crystallization method for high performance polycrystalline silicon (poly-Si) thin-film transistors (TFTs) using Ni silicide seed-induced lateral crystallization (SILC) was proposed in this study, and it includes no additional deposition and/or etching processes that are not found in the fabrication of conventional metal-induced lateral crystallization (MILC) TFTs. The poly-Si thin films crystallized by SILC were characterized by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and Micro-Raman spectroscopy. The electrical properties were obtained from I D - V G transfer curves and the interface trap density was determined by Levinson plot analysis. The results show that SILC poly-Si films have lower Ni contamination, better crystallinity, and higher crystalline fraction than MILC poly-Si films. The p-channel SILC poly-Si TFTs exhibited a mobility of 66 cm2/Vs, a minimum leakage current of 3.4 10-11 A at V D = -5 V, a subthreshold slope of 0.85 V/dec, and a maximum on/off ratio of 5.0 106, all of which resulted in a high-performance device which surpassed conventional MILC poly-Si TFTs.

Byun, Chang Woo; Son, Se Wan; Lee, Yong Woo; Joo, Seung Ki

2012-06-01

116

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

NASA Astrophysics Data System (ADS)

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.

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

2013-03-01

117

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

PubMed

The effects of process conditions, including upward velocity inside the column, the amount of added seed and seed size, the pH value of the precipitant or the phosphate stream and the Ba/P molar ratio in a fluidized-bed reactor (FBR) were studied with a view to producing BaHPO? crystals of significant size and maximize the removal of barium. XRD were used to identify the products that were collected from the FBR. Experimental results show that an upward velocity of 48 cmmin(-1) produced the largest BaHPO? crystals with a size of around 0.84-1.0mm. The addition of seed crystals has no effect on barium removal. The use of a seed of a size in the ranges unseeded<0.149-0.29 mm<0.149 mm<0.29-0.42 mm produced increasing amounts of increasingly large crystals. The largest BaHPO? crystals were obtained at pH 8.4-8.8 with a Ba/P molar ratio of 1.0. In the homogeneous and heterogeneous processes, around 98% of barium was removed at pH 8.4-8.6 and [Ba]/[P]=1.0. The XRD results show that a significant amount of barium phosphate (Ba?(PO?)?) was obtained at pH 11. The compounds BaHPO? and BaO were present at a pH of below 10. PMID:24462085

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

2014-06-01

118

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

PubMed

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

Naidu, Sonia; Scherer, George W

2014-12-01

119

Lattice Boltzmann Simulation of Calcite Precipitation and Isotope Fractionation  

NASA Astrophysics Data System (ADS)

The Lattice-Boltzmann (LB) method can be used to simulate aspects of chemical reactions such as vapor condensation or mineral precipitation from a fluid phase. It has the advantage of allowing the solute phase to evolve depending on local conditions rather than being specified, so that the controls on precipitated phase grain shape can be studied simultaneously with the controls on chemical compositions and growth rate. We have used the LB approach to simulate the precipitation of calcite from oversaturated water as an effort in developing methods for treating complex chemical reaction problems, including isotopic effects. The formation of calcite is a classic problem in diffusion and reaction-limited mineral growth. There are many complexities, but the process is attractive for modeling purposes because there is abundant information on reaction kinetics and the relationships between crystal morphology and growth conditions. In this paper we describe the LB approach used, address strategies for properly conserving mass at a surface of a growing 73"0?crystal?73"0?"08, the scaling of the calculations to the actual physical problem, and the conditions for growth of dendritic versus compact crystals.

Lu, G.; Depaolo, D.; Kang, Q.; Zhang, D.

2008-12-01

120

Do organic ligands affect calcite dissolution rates?  

NASA Astrophysics Data System (ADS)

Steady state Iceland-spar calcite dissolution rates were measured at 25 C in aqueous solutions containing 0.1 M NaCl and up to 0.05 M dissolved bicarbonate at pH from 7.9 to 9.1 in the presence of 13 distinct dissolved organic ligands in mixed-flow reactors. The organic ligands considered in this study include those most likely to be present in either (1) aquifers at the conditions pertinent to CO 2 sequestration or (2) soil/early diagenetic environments: acetate, phthalate, citrate, EDTA 4-, succinate, D-glucosaminate, L-glutamate, D-gluconate, 2,4-dihydroxybenzoate, 3,4-dihydroxybenzoate, fumarate, malonate, and gallate. Results show that the presence of <0.05 mol/kg of these organic anions changes calcite dissolution rates by less than a factor of 2.5 with the exception of citrate and EDTA 4-. The presence of 0.05 mol/kg citrate and EDTA 4- increases calcite dissolution rates by as much as a factor of 35 and 500, respectively, compared to rates in organic anion-free solutions. Further calcite dissolution experiments were performed in the presence of organic polymers similar to bacterial exudates, cell exopolysaccharides, and analogs of microbial cell envelopes: alginate, lichen extract, humic acid, pectin, and gum xanthan. In no case did the presence of <100 ppm of these organics change calcite dissolution rates by more than a factor of 2.5. Results obtained in this study suggest that the presence of aqueous organic anions negligibly affects calcite forward dissolution rates in most natural environments. Some effect on calcite reactivity may be observed, however, by the presence of organic anions if they change substantially the chemical affinity of the fluid with respect to calcite.

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

2011-04-01

121

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

SciTech Connect

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

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

2012-05-01

122

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

NASA Technical Reports Server (NTRS)

An in-situ monitoring furnace was constructed with side windows to perform partial pressure measurements by optical absorption and visual observation of the growing crystal. A fused silica -rowth ampoule with a 4.5 cm long square tube between the source and the seed was prepared for the optical absorption measurements. A ZnSe crystal was grown by the seeded physical vapor transport (PVT) technique in the horizontal configuration. The growth temperature was 1120 C and the furnace translation rate was 3nmVday. Partial pressures of Se2, P(sub Se2), at three locations along the length of the growth ampoule were measured at 90 min intervals during the growth process. The measured P (sub Se2) were in the range of 2.0 to 6.5 x 10(exp -3) atm. The P(sub Se2) results indicated that the partial pressure profile was inconsistent with the results of the one-dimensional diffusion mass transport model and that the source composition shifted toward Se-rich during the run, i.e. the grown crystal was more Zn-rich than the source. The visual observation showed that the seed crystal first etched back, with greater thermal etching occurring along the edges of the seed crystal. Once the growth started, the crystal crew in a predominately contactless mode and facets were evident during growth. The crystal did not grow symmetrically which is believed to be due to the unintentional asymmetry of the radial thermal profile in the furnace.

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

1999-01-01

123

Timing and mechanism of late-Pleistocene calcite vein formation across the Dead Sea Fault Zone, northern Israel  

NASA Astrophysics Data System (ADS)

The emplacement of calcite-filled veins perpendicular to the Dead Sea Fault Zone in northern Israel reflects strain partitioning during transpression. We present structural, geochemical, and U-Th geochronological data that constrain the mechanism, conditions and timing of vein formation. Vein walls are strongly brecciated and commonly cemented with coarsely crystalline calcite, whereas calcite-filled veins are composed of wall-parallel bands of calcite crystals. Elongated blocky and fibrous calcite crystals grew perpendicular to the vein walls and are characterised by a truncate sealing-hiatus morphology, indicating episodes of partial or complete sealing of the fractures during calcite precipitation. Stable isotope and rare-earth element and yttrium (REY) analyses indicate that calcite-filled veins precipitated by karst processes, involving meteoric water and limited fluid-rock interactions. U-Th dating results show a prolonged history of vein growth. While some veins initiated prior to 500 ka, the majority of the veins were active between 358 and 17 ka. Age constraints on vein activity correspond to an E-W regional shortening phase in this sector of the Dead Sea Fault Zone, associated with an increased component of convergence during the late-Pleistocene.

Nuriel, Perach; Weinberger, Ram; Rosenbaum, Gideon; Golding, Suzanne D.; Zhao, Jian-xin; Tonguc Uysal, I.; Bar-Matthews, Miryam; Gross, Michael R.

2012-03-01

124

Precipitation of calcite induced by Synechocystis sp. PCC6803.  

PubMed

Calcite with laminate structure was successfully prepared by culturing Synechocystis sp. PCC6803 with different concentrations of calcium chloride (CaCl?) in BG11 media. S. PCC6803 was examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), laser confocal scanning microscope (LCSM) and energy dispersive spectroscopy (EDS). The effects of Ca? concentrations and pH values on calcification were investigated and the micro morphs of the CaCO? crystals were observed by means of SEM. These results showed that CaCO? crystals could be more easily formed with increasing the concentration of CaCl? in S. PCC6803 culture solution. S. PCC6803 could largely bind calcium ions, most of which were present in extracellular polymeric substances and on the cell wall. Inside the cells there were a lot of circular areas rich in calcium ions without the crystallization of calcium. Some cells produced a thicker gelatinous sheath outside of the translucent organic thin layer. And the cells inside also produced major changes that the original chloroplasts were almost transformed into starch grains whose sizes were from 0.5 to 1 ?m with relatively uniform in sizes. At the same time the cell sizes significantly reduced to only about 8-9 ?m almost changing to half of its original diameters. The calcite crystals with a highly preferred orientation induced by S. PCC6803 were observed with X-ray diffraction (XRD). A critical implication was that S. PCC6803 could induce bio-calcification and then mediate the further growth of CaCO? crystals in the biological system. PMID:23543209

Han, Zuozhen; Yan, Huaxiao; Zhou, Shixue; Zhao, Hui; Zhang, Yan; Zhang, Ningning; Yao, Chuankai; Zhao, Lin; Han, Chunyan

2013-10-01

125

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

NASA Astrophysics Data System (ADS)

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.

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

2014-01-01

126

Sea Urchin Spine Calcite Forms via a Transient Amorphous Calcium Carbonate Phase  

Microsoft Academic Search

The skeletons of adult echinoderms comprise large single crystals of calcite with smooth convoluted fenestrated morphologies, raising many questions about how they form. By using water etching, infrared spectroscopy, electron diffraction, and environmental scanning electron microscopy, we show that sea urchin spine regeneration proceeds via the initial deposition of amorphous calcium carbonate. Because most echinoderms produce the same type of

Yael Politi; Talmon Arad; Eugenia Klein; Steve Weiner; Lia Addadi

2004-01-01

127

Calcite Deposition during Shell Repair by the Aragonitic Gastropod Murex fulvescens  

Microsoft Academic Search

Shell repair was induced by coating the inner surfaces of gastropod shells with nail polish. In aragonitic gastropods initial deposition on the nail-polish membrane was of aragonite spherulites and, in one species, polygonal calcite crystals; later the normal crossed-lamellar structure of the shell was restored.

E. O. Muzii; H. Catherine W. Skinner; W. Skinner

1966-01-01

128

High performance poly-Si thin film transistors fabricated by self-aligned seed induced lateral crystallization  

NASA Astrophysics Data System (ADS)

In this study, a low temperature polycrystalline silicon (LTPS) thin-film transistor (TFT) was fabricated by self-aligned silicide seed induced lateral crystallization (SA-SILC). In comparison with a self-aligned metal induced lateral crystallization (SA-MILC) TFT, the SA-SILC TFT showed better electrical properties. In particular, the leakage current was decreased by SA-SILC at high drain voltages. It was found that the Ni rich phase between the channel and drain junction region acted as trapping sites to generate leakage current by thermionic field emission. After applying the SA-SILC process, the p-channel polycrystalline silicon (poly-Si) TFT exhibited a mobility of 67 cm 2/Vs, a minimum leakage current of 2.6 10-11 A at V D = -5 V, a subthreshold slope of 0.8 V/dec, and a maximum on/off ratio of 7.0 10 6, together resulting in a high-performance device that surpasses the conventional SA-MILC poly-Si TFT.

Byun, Chang Woo; Son, Se Wan; Lee, Yong Woo; Yun, Seung Jae; Lee, Sang Joo; Joo, Seung Ki

2011-12-01

129

Upscaling Calcite Growth Rates From the Mesoscale to the Macroscale  

SciTech Connect

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.

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

2013-01-01

130

Calcite dissolution in two deep eutrophic lakes  

SciTech Connect

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.

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

1999-10-01

131

Integrated Approach for Understanding Impurity Adsorption on Calcite: Mechanisms for Micro-scale Surface Phenomena  

NASA Astrophysics Data System (ADS)

A longstanding goal within the field of environmental geochemistry has been the development of a fundamental understanding of the kinetics that governs the interactions of solution-borne impurities with the calcite mineral surface. Recent dissolution experiments using Mg2+, Mn2+, and Sr2+ have shown distinct differences in the interaction of these three impurity ions with the calcite crystal surface. Because the dissolution of carbonate minerals in soils and sediments influences the uptake and migration of groundwater contaminants, a rigorous understanding of the basic processes that occur at the mineral-fluid interface is necessary. We have used vertical scanning interferometry (VSI) coupled with scanning probe microscopy (SPM) to examine calcite crystal dissolution in the presence of Mg2+, Mn2+, and Sr2+, all known dissolution inhibitors and possible groundwater contaminants. We have studied the kinetics of impurity-crystal interactions at a pH 8.8, and in the presence or absence of dissolved inorganic carbon. Our data show that, when individually introduced into undersaturated solutions, Mg2+ and Mn2+ are shown to activate the calcite crystal surface, resulting in enhanced etch pit nucleation rates and step density. Conversely, Sr2+ is shown to cause passivation of the calcite surface. The effect is intensified when solutions are saturated with respect to atmospheric CO2. Results indicate that aqueous CO32- (or HCO3-) may influence how aqueous metal ionic complexes interact with the crystal surface. Furthermore, the influence is differently exhibited, and passivation or activation ultimately depends on the properties of the diffusing metal ion or metal-hydroxide complex. These properties include for example, differences in hydration enthalpy, the effective ionic radius, and electron shell configuration.

Vinson, M. D.; Arvidson, R. S.; Luttge, A.

2004-12-01

132

Effects of molten salt synthesis (MSS) parameters on the morphology of Sr 3 Ti 2 O 7 and SrTiO 3 seed crystals  

Microsoft Academic Search

A two-step molten salt synthesis process was utilized to fabricate Sr3Ti2O7 and SrTiO3. High aspect ratio SrTiO3 seed crystals were developed by optimizing processing conditions such as temperature, salt-to-oxide ratio, and flux type\\u000a in a systematic fashion. Sr3Ti2O7 seeds were synthesized at temperatures ranging from 10501350C, using salt-to-oxide ratios of 3:1, 1:1, and 1:3, and various\\u000a salt types, including NaCl,

E. K. Akdogan; Raymond Edwin Brennan; Mehdi Allahverdi; Ahmad Safari

2006-01-01

133

Coprecipitation of Uranium(VI) with Calcite: XAFS, micro-XAS, and luminescence characterization  

NASA Astrophysics Data System (ADS)

X-ray absorption and luminescence spectroscopies have been used to characterize the local structure and coordination of uranium(VI) species coprecipitated with calcite (CaCO 3) from room-temperature aqueous solutions. Different solution chemistries and pHs are found to result in differences in the equatorial coordination of the uranyl species (UO 22+) incorporated in the calcite, with multiple coordination environments of uranyl evident in one sample. Differences in the equatorial coordination between the aqueous uranyl species and those found in the calcite indicate that coordination changes occur during incorporation of at least some species. This contrasts with previous findings showing no change in equatorial coordination during uranyl incorporation into aragonite, and may explain the greater incorporation in this latter phase. The absence of calcium backscatterers and well defined structure beyond the equatorial shell is consistent with disorder associated with disruption of the local calcite structure. This may indicate an inability of the uranyl unit to assume a stable structural environment in the host calcite, which could decrease the stability of uranyl-containing calcite. Calcite single crystals grown in uranyl-containing solutions exhibit polygonized spiral growth hillocks on (1014) surfaces composed of four vicinal surfaces, consistent with face symmetry. Micro-X-ray fluorescence reveals that uranium is differentially incorporated between nonequivalent vicinal surfaces, reflecting step-selective incorporation of uranyl species during growth. Micro-X-ray absorption near-edge structure spectra from the nonequivalent vicinal faces fail to reveal any differences in speciation between the vicinals or that might account for the presence of the multiple coordination environments identified by luminescence and X-ray absorption spectroscopies.

Reeder, Richard J.; Nugent, Melissa; Tait, C. Drew; Morris, David E.; Heald, Steve M.; Beck, Kenneth M.; Hess, Wayne P.; Lanzirotti, Anthony

2001-10-01

134

Oxygen isotopes in calcite grown under cave-analogue conditions  

NASA Astrophysics Data System (ADS)

Speleothem oxygen isotopes and growth rates are valuable proxies for reconstructing climate history. There is debate, however, about the conditions that allow speleothems to grow in oxygen isotope equilibrium, and about the correct equilibrium fractionation factors. We report results from a series of carbonate growth experiments in karst-analogue conditions in the laboratory. The setup closely mimics natural processes (e.g. precipitation driven by CO 2-degassing, low ionic strength solution, thin solution film) but with a tight control on growth conditions (temperature, pCO 2, drip rate, calcite saturation index and the composition of the initial solution). Calcite is dissolved in water in a 20,000 ppmV pCO 2 environment. This solution is dripped onto glass plates (coated with seed-carbonate) in a lower pCO 2 environment (<2500 ppmV), where degassing leads to calcite growth. Experiments were performed at 7, 15, 25 and 35 C. At each temperature, calcite was grown at three drip rates (2, 6 and 10 drips per minute) on separate plates. The mass of calcite grown in these experiments varies with temperature ( T in K) and drip rate ( d_ r in drips min -1) according to the relationship daily growth mass = 1.254 + 1.478 ? 10 -9 ? e0.0679 T + ( e0.00248 T - 2) ? (-0.779 d_ r2 + 10.05 d_ r + 11.69). This relationship indicates a substantial increase of growth mass with temperature, a smaller influence of drip rate on growth mass at low temperature and a non-linear relationship between drip rate and growth mass at higher temperatures. Low temperature, fast dripping conditions are found to be the most favourable for reducing effects associated with evaporation and rapid depletion of the dissolved inorganic carbon reservoir (rapid DIC-depletion). The impact of evaporation can be large so caves with high relative humidity are also preferable for palaeoclimate reconstruction. Even allowing for the maximum offsets that may have been induced by evaporation and rapid DIC-depletion, ? 18O measured in some of our experiments remain higher than those predicted by Kim and O'Neil (1997). Our new results are well explained by equilibrium at a significantly higher ?calcite-water, with a kinetic-isotope effect that favours 16O incorporation as growth rate increases. This scenario agrees with recent studies by Coplen (2007) and Dietzel et al. (2009). Overall, our results suggest that three separate processes cause ? 18O to deviate from true isotope equilibrium in the cave environment. Two of these drive ? 18O to higher values (evaporation and rapid DIC-depletion) while one drives ? 18O to lower values (preferential incorporation of 16O in the solid carbonate at faster growth rates). While evaporation and DIC-depletion can be avoided in some settings, the third may be inescapable in the cave environment and means that any temperature to ? 18O relationship is an approximation. The controlled conditions of the present experiments also display limitations in the use of the Hendy test to identifying equilibrium growth.

Day, C. C.; Henderson, G. M.

2011-07-01

135

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

NASA Technical Reports Server (NTRS)

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.

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

2014-01-01

136

Nanocrystalline calcitic lens arrays fabricated by self-assembly followed by amorphous-to-crystalline phase transformation.  

PubMed

Natural calcium carbonate-based nanocomposites often have superior physical properties and provide a comprehensive source for bioinspired synthetic materials. Here we present thermodynamically stable, transparent CaCO3 microlens arrays (MLA) produced by transforming an amorphous CaCO3 phase into nanocrystalline calcite. We analyze the structure and properties of crystallized MLA by X-ray scattering, transmitted and polarized light microscopy, and electron microscopy and find that MLA are crystallized in spherulite-like patterns without changing the shape of the microlens. The key finding is that nanocrystallinity of the calcite formed diminishes structural anisotropy on the wavelength scale and results in greatly reduced birefringent effects. The remnant preferred orientation of the optical axes of calcite crystals in the plane of the microlens arrays leads to some directionality of optical properties, which may be beneficial for technical applications. PMID:25117467

Schmidt, Ingo; Lee, Kyubock; Zolotoyabko, Emil; Werner, Peter; Shim, Tae Soup; Oh, You-Kwan; Fratzl, Peter; Wagermaier, Wolfgang

2014-09-23

137

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

NASA Technical Reports Server (NTRS)

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.

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

2001-01-01

138

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

139

Calcite Reaction Kinetics in Saline Waters  

E-print Network

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

Finneran, David

2012-02-14

140

Seeded crystal growth of YBa{sub 2}Cu{sub 3}O{sub 6.5} in semisolid melts  

SciTech Connect

Melt textured single crystals of YBa{sub 2}Cu{sub 3}O{sub 6.5} (123) superconductors were produced by isothermal solidification from a semisolid melt using single crystal NdBa{sub 2}Cu{sub 3}O{sub 6.5} or SmBa{sub 2}Cu{sub 3}O{sub 6.5} seeds. The microstructure within the single crystals shows an inhomogeneous segregation of Y{sub 2}BaCuO{sub 5} (211) particles trapped in the 123 crystals during solidification. The concentration of 211 particles varies with the crystal axes in 123 crystals produced from precursors with compositions of 80 wt.{percent} 123 powder and 20 wt.{percent} excess 211. The 211 particle concentration along the c-axis in the crystal is much lower than that along the a- or b-axes during initial crystallization. This concentration increases in both directions as the crystal grows larger. The 211 concentration along the c-axis increases more quickly than the concentration along the other axes during solidification, which allows the 211 concentration to approach that on the other axes as the solidification continues. 211 particle segregation in stoichiometric 123 samples formed {open_quotes}X{close_quotes}-shaped tracks instead of the variations in 211 concentration described above. A single crystal growth model of 123 is proposed and employed to interpret these experimental observations. Quenched samples were prepared to investigate the volume fraction of 211 particles in the liquid phase. A constant distribution of 211 particles was observed in the liquid, except very near the crystal interface, where the 211 concentration decreased rapidly. Copper oxide content in the liquid was also measured. It is found that the copper content is lower at the (001) interface compared with (100) or (010) interfaces. {copyright} {ital 1997 Materials Research Society.}

Honjo, S.; Cima, M.J.; Flemings, M.C.; Ohkuma, T.; Shen, H.; Rigby, K.; Sung, T.H. [Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

1997-04-01

141

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

142

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)  

Microsoft Academic Search

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+}, CO²⁻, ClO⁻, and\\/or Cl⁻. LEED results demonstrate that the calcite surface is atomically

S. L. Stipp; M. F. Jr. Hochella; G. A. Parks; J. O. Leckie

1992-01-01

143

Paired gill slits in a fossil with a calcite skeleton.  

PubMed

The chordates, hemichordates (such as acorn worms) and echinoderms (such as starfish) comprise the group Deuterostomia, well established as monophyletic. Among extant deuterostomes, a skeleton in which each plate has the crystallographic structure of a single crystal of calcite is characteristic of echinoderms and is always associated with radial symmetry and never with gill slits. Among fossils, however, such a skeleton sometimes occurs without radial symmetry. This is true of Jaekelocarpus oklahomensis, from the Upper Carboniferous of Oklahoma, USA, which, being externally almost bilaterally symmetrical, is traditionally placed in the group Mitrata (Ordovician to Carboniferous periods, 530-280 million years ago), by contrast with the bizarrely asymmetrical Cornuta (Cambrian to Ordovician periods, 540 to 440 million years ago). Using computer X-ray microtomography, we describe the anatomy of Jaekelocarpus in greater detail than formerly possible, reveal evidence of paired gill slits internally and interpret its functional anatomy. On this basis we suggest its phylogenetic position within the deuterostomes. PMID:12075349

Dominguez, Patrcio; Jacobson, Antone G; Jefferies, Richard P S

2002-06-20

144

Understanding control of calcitic biomineralization-proteomics to the rescue.  

PubMed

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

Hincke, Maxwell T

2013-12-01

145

Shock-induced effects in calcite from Cactus Crater  

NASA Technical Reports Server (NTRS)

The paper discusses shock metamorphism of calcite from coralline limestone samples retrieved from a borehole drilled into rocks beneath Cactus Crater, a nuclear explosion crater at Eniwetok Atoll. The metamorphism was detected and quantified using electron spin resonance (ESR); the ESR spectra of Mn(+) present as a trace constituent in the coral samples, show a consistent decrease in hyperfine peak splitting with decreasing depth of sample. It is suggested that the decrease in hyperfine peak splitting reflects a decrease in crystal field splitting, and therefore, small increases on cation-anion distances produced by mechanical energy input during the shock process. Two alternative crater models suggested by the ESR results are a depiction of a steady decay of the shock wave, and a delineation of a breccia lens with a breccia-bedrock interface at 20 plus or minus 5 m.

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

1980-01-01

146

Controls on trace-element partitioning in cave-analogue calcite  

NASA Astrophysics Data System (ADS)

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

Day, Christopher C.; Henderson, Gideon M.

2013-11-01

147

& Microarrays Calcite Microneedle Arrays Produced by Inorganic Ion-Assisted  

E-print Network

& Microarrays Calcite Microneedle Arrays Produced by Inorganic Ion-Assisted Anisotropic Dissolution solution in the presence of ammo- nium salts. The lengths and the aspect ratios of the calcite microneedles of the calcite microneedles could be attributed to the tri-symmetric feature of rhombohedral cal- cite atomic

Qi, Limin

148

Microstructures and rheology of a calcite-shale thrust fault  

NASA Astrophysics Data System (ADS)

A thin (2 cm) layer of extensively sheared fault rock decorates the 15 km displacement Copper Creek thrust at an exposure near Knoxville, TN (USA). In these ultrafine-grained (<0.3 ?m) fault rocks, interpenetrating calcite grains form an interconnected network around shale clasts. One cm below the fault rock layer, sedimentary laminations in non-penetratively deformed footwall shale are cut by calcite veins, small faults, and stylolites. A 350 ?m thick calcite vein separates the fault rocks and footwall shale. The vein is composed of layers of (1) coarse calcite grains (>5 ?m) that exhibit a lattice preferred orientation (LPO) with pores at twin-twin and twin-grain boundary intersections, and (2) ultrafine-grained (0.3 ?m) calcite that exhibits interpenetrating grain boundaries, four-grain junctions and lacks a LPO. Coarse calcite layers crosscut ultrafine-grained layers indicating intermittent vein formation during shearing. Calcite in the fault rock layer is derived from vein calcite and grain-size reduction of calcite took place by plasticity-induced fracture. The ultrafine-grained calcite deformed primarily by diffusion-accommodated grain boundary sliding and formed an interconnected network around shale clasts within the shear zone. The interconnected network of ultrafine-grained calcite indicates that calcite, not shale, was the weak phase in this fault zone.

Wells, Rachel K.; Newman, Julie; Wojtal, Steven

2014-08-01

149

in situ Calcite Precipitation for Contaminant Immobilization  

SciTech Connect

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 DOEs 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.

Yoshiko Fujita; Robert W. Smith

2009-08-01

150

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

SciTech Connect

Calcite vein and vug fillings at four depths (130-314m), all above the present water table in USW G-1 bore hole at Yucca Mountain, Nevada, contain primary fluid inclusions with variable vapor/liquid raitos: Most of these inclusions are either full of liquid or full of vapor. The liquid-filled inclusions show that most of the host calcite crystallized from fluids at <100{degrees}C. The vapor-filled inclusions provide evidence that a separate vapor phase was present in the fluid during crystallization. Studies of these vapor-filled inclusions on the microscope crushing stage were interpreted in an earlier paper as indicating trapping of an air-water-CO{sub 2} vapor phase at ``<100{degrees}C``. Our new studies reveal the additional presence of major methane in the vapor-filled inclusion, indicating even lower temperatures of trapping, perhaps at near-surface temperatures. They also show that the host calcite crystals grew from a flowing film of water on the walls of fractures open to the atmosphere, the vapor-filled inclusions representing bubbles that exsolved from this film onto the crystal surface.

Roedder, E. [Harvard Univ., Cambridge, MA (United States); Whelan, J.F. [Geological Survey, Denver, CO (United States); Vaniman, D.T. [Los Alamos National Lab., NM (United States)

1994-12-31

151

Calcium-43 NMR studies of polymorphic transition of calcite to aragonite.  

PubMed

Phase transformation between calcite and aragonite is an important issue in biomineralization. To shed more light on the mechanism of this process at the molecular level, we employ solid-state (43)Ca NMR to study the phase transformation from calcite to aragonite as regulated by magnesium ions, with (43)Ca enrichment at a level of 6%. Using the gas diffusion approach, the phase of Mg-calcite is formed initially and the system subsequently transforms to aragonite as the reaction time proceeds. Our (43)Ca solid-state NMR data support the dissolution-recrystallization mechanism for the calcite to aragonite transition. We find that the (43)Ca NMR parameters of Mg-calcite are very similar to those of pure calcite. Under the high-resolution condition provided by magic-angle spinning at 4 kHz, we can monitor the variation of the (43)Ca NMR parameters of the aragonite signals for the samples obtained at different reaction times. Our data suggest that in the presence of a significant amount of Mg(2+) ions, aragonite is the most stable polymorph of calcium carbonate. The initial precipitated crystallites of aragonite have spine-like morphology, for which the (43)Ca spin-lattice relaxation data indicate that the ions in the lattice have considerable motional dynamics. As the crystallinity of aragonite improves further, the (43)Ca T(1) parameter of the aragonite phase changes considerably and becomes very similar to that obtained for pure aragonite. For the first time, the difference in crystal morphologies and crystallinity of the aragonite phase has been traced down to the subtle difference in the motional dynamics at the molecular level. PMID:23163540

Huang, Yu-Chieh; Mou, Yun; Tsai, Tim Wen-Tin; Wu, Yu-Ju; Lee, Hsin-Kuan; Huang, Shing-Jong; Chan, Jerry C C

2012-12-13

152

Calcite growth-rate inhibition by fulvic acid and magnesium ionPossible influence on biogenic calcite formation  

USGS Publications Warehouse

Increases in ocean surface water dissolved carbon dioxide (CO2) concentrations retard biocalcification by reducing calcite supersaturation (?c). Reduced calcification rates may influence growth-rate dependent magnesium ion (Mg) incorporation into biogenic calcite modifying the use of calcifying organisms as paleoclimate proxies. Fulvic acid (FA) at biocalcification sites may further reduce calcification rates. Calcite growth-rate inhibition by FA and Mg, two common constituents of seawater and soil water involved in the formation of biogenic calcite, was measured separately and in combination under identical, highly reproducible experimental conditions. Calcite growth rates (pH=8.5 and ?c=4.5) are reduced by FA (0.5 mg/L) to 47% and by Mg (10?4 M) to 38%, compared to control experiments containing no added growth-rate inhibitor. Humic acid (HA) is twice as effective a calcite growth-rate inhibitor as FA. Calcite growth rate in the presence of both FA (0.5 mg/L) and Mg (10?4 M) is reduced to 5% of the control rate. Mg inhibits calcite growth rates by substitution for calcium ion at the growth site. In contrast, FA inhibits calcite growth rates by binding multiple carboxylate groups on the calcite surface. FA and Mg together have an increased affinity for the calcite growth sites reducing calcite growth rates.

Reddy, Michael M.

2012-01-01

153

Low-temperature crystallization of oriented ZnO film using seed layers prepared by solgel method  

Microsoft Academic Search

Transparent zinc oxide (ZnO) films were coated on seed layers prepared by the solgel method by chemical solution deposition\\u000a method. Firstly, seed layers were prepared from zinc acetate and monoethanolamine, 2-methoxyethanol by the solgel method\\u000a on a silicon substrate or a slide glass. Next, the substrate coated with a seed layer was immersed in zinc nitride solution\\u000a with hexamethylenetetramine, and

Hiroyo Segawa; Hideaki Sakurai; Reiko Izumi; Toshiharu Hayashi; Tetsuji Yano; Shuichi Shibata

2011-01-01

154

Third-Order Elastic Constants of Calcite  

Microsoft Academic Search

The third-order elastic constants of calcite at 0C have been determined by measuring the stress and temperature dependence of sound velocities in it by means of an improved pulse-superposition method (average sensitivity of 210-7). Within the small temperature range considered (about 2C), a nonlinear temperature dependence which varies with pressure has been clearly observed. Out of 14 independent third-order moduli,

H. Kaga

1968-01-01

155

Shock Compression of Crustal Rocks: Data for Quartz, Calcite, and Plagioclase Rocks  

Microsoft Academic Search

ttugoniot data in the 4- to 250-kb stress range were obtained for quartzite and novaculite, sandstones of varying porosity, single-crystal calcite, marble, porous and non- porous limestone, several plagioclases of varying composition, and a basalt. Conventional plane-wave, in-contact explosive assemblies were used; the shock state was computed from measured shock velocities; particle velocities are inferred from either specimen or driver

Thomas J. Ahrens; V. G. Gregson

1964-01-01

156

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

NASA Astrophysics Data System (ADS)

We investigated the dissolution behaviour of polished calcite surfaces in situ using a fluid-cell atomic force microscope. Polished calcite surfaces enabled us to study the effects of applied surface stress and crystallographic orientation on calcite dissolution pattern formation. Thin-sections of Iceland spar single-crystals polished either parallel or with a 5 miscut angle to {1014} cleavage planes were studied. Compressive surface stresses of up to 50 MPa were applied to some of the thin-section samples by means of elastic concave bending. Experiments were carried out in semi-stagnant deionized water under mainly transport limited dissolution conditions. Samples polished parallel to {1014} cleavage planes dissolved by the formation of etch-pits originating from polishing defects. The dissolution behaviour of 5 miscut surfaces was relatively unaffected by polishing defects, since no etch-pits developed in these samples. Dissolution of the miscut samples led to stepped or rippled surface patterns on the nanometer scale that coarsened during the first 30-40 min of the experiments. Possible reasons for the pattern-coarsening were: (i) progressive bunching of retreating dissolution steps and (ii) surface energy driven recrystallization (Ostwald ripening) under transport limited dissolution conditions. A flat polished miscut surface in calcite may recrystallize into a hill-and-valley structure in a (near-)saturated solution so as to lower its total surface free energy in spite of a larger surface area. No clear effect of applied stress on dissolution pattern formation has been observed.

Bisschop, J.; Dysthe, D. K.; Putnis, C. V.; Jamtveit, B.

2006-04-01

157

Comparison of solidification/stabilization effects of calcite between Australian and South Korean cements  

SciTech Connect

The differences in the effect of calcite on the strength and stability of Pb-rich wastes solidified and stabilized using Australian and South Korean ordinary Portland cements are examined in this study. Pb-rich waste stabilized using Australian OPC has been shown to possess both substantially higher unconfined compressive strength and lead immobilization ability than South Korean OPC as a result of its higher C{sub 3}S content and the associated enhanced degree of precipitation of lead on the surfaces of silicate phases present. Calcite addition is observed to have an accelerating effect on the OPC-induced solidification/stabilization of Pb-rich wastes as gauged by the unconfined compressive strength and leachability of the solids formed. This effect is observed to be far more dramatic for South Korean OPC than for Australian OPC. Using scanning electron microscopy, waste stabilized with cement and calcite was observed to develop significantly greater proportions of hydrated crystals than wastes stabilized with cement alone. The results of X-ray diffraction studies have shown that the presence of calcite in South Korean OPC results in greater acceleration in the formation of portlandite than is the case for Australian OPC.

Lee, Dongjin [School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); Waite, T. David [School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia)]. E-mail: d.waite@unsw.edu.au; Swarbrick, Gareth [School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); Lee, Sookoo [School of Environmental Engineering, Seoul National University of Technology, Nowon-Gu, Seoul, 139-743 (Korea, Republic of)

2005-11-15

158

Removal of organic magnesium in coccolithophore calcite  

NASA Astrophysics Data System (ADS)

Coccolithophore calcite refers to the plates of calcium carbonate (CaCO3) produced by the calcifying phytoplankton, coccolithophores. The empirical study of the elemental composition has a great potential in the development of paleoproxies. However, the difficulties to separate coccolithophore carbonates from organic phases hamper the investigation of coccoliths magnesium to calcium ratios (Mg/Ca) in biogeochemical studies. Magnesium (Mg) is found in organic molecules in the cells at concentrations up to 400 times higher than in inorganically precipitated calcite in present-day seawater. The aim of this study was to optimize a reliable procedure for organic Mg removal from coccolithophore samples to ensure reproducibility in measurements of inorganic Mg in calcite. Two baseline methods comprising organic matter oxidations with (1) bleach and (2) hydrogen peroxide (H2O2) were tested on synthetic pellets, prepared by mixing reagent grade CaCO3 with organic matter from the non-calcifying marine algae Chlorella autotrophica and measured with an ICP-AES (inductively coupled plasma-atomic emission spectrometer). Our results show that treatments with a reductive solution [using hydroxylamine-hydrochloride (NH2OHHCl + NH4OH)] followed by three consecutive oxidations (using H2O2) yielded the best cleaning efficiencies, removing >99% of organic Mg in 24 h. P/Ca and Fe/Ca were used as indicators for organic contamination in the treated material. The optimized protocol was tested in dried coccolithophore pellets from batch cultures of Emiliania huxleyi, Calcidiscus leptoporus and Gephyrocapsa oceanica. Mg/Ca of treated coccolithophores were 0.151 0.018, 0.220 0.040, and 0.064 0.023 mmol/mol, respectively. Comparison with Mg/Ca literature coccolith values, suggests a tight dependence on modern seawater Mg/Ca, which changes as a consequence of different seawater origins (<10%). The reliable determination of Mg/Ca and Sr/Ca, and the low levels of organic contamination (Fe/Ca and P/Ca) make this protocol applicable to field and laboratory studies of trace elemental composition in coccolithophore calcite.

Blanco-Ameijeiras, S.; Lebrato, M.; Stoll, H. M.; Iglesias-Rodriguez, M. D.; Mndez-Vicente, A.; Sett, S.; Mller, M. N.; Oschlies, A.; Schulz, K. G.

2012-07-01

159

Reaction mechanism for the replacement of calcite by dolomite and siderite: implications for geochemistry, microstructure and porosity evolution during hydrothermal mineralisation  

NASA Astrophysics Data System (ADS)

Carbonate reactions are common in mineral deposits due to CO2-rich mineralising fluids. This study presents the first in-depth, integrated analysis of microstructure and microchemistry of fluid-mediated carbonate reaction textures at hydrothermal conditions. In doing so, we describe the mechanisms by which carbonate phases replace one another, and the implications for the evolution of geochemistry, rock microstructures and porosity. The sample from the 1.95 Moz Junction gold deposit, Western Australia, contains calcite derived from carbonation of a metamorphic amphiboleplagioclase assemblage that has further altered to siderite and dolomite. The calcite is porous and contains iron-rich calcite blebs interpreted to have resulted from fluid-mediated replacement of compositionally heterogeneous amphiboles. The siderite is polycrystalline but nucleates topotactically on the calcite. As a result, the boundaries between adjacent grains are low-angle boundaries (<10), which are geometrically similar to those formed by crystal-plastic deformation and recovery. Growth zoning within individual siderite grains shows that the low-angle boundaries are growth features and not due to deformation. Low-angle boundaries develop due to the propagation of defects at grain faces and zone boundaries and by impingement of grains that nucleated with small misorientations relative to each other during grain growth. The cores of siderite grains are aligned with the twin planes in the parent calcite crystal showing that the reactant Fe entered the crystal along the twin boundaries. Dolomite grains, many of which appear to in-fill space generated by the siderite replacement, also show alignment of cores along the calcite twin planes, suggesting that they did not grow into space but replaced the calcite. Where dolomite is seen directly replacing calcite, it nucleates on the Fe-rich calcite due to the increased compatibility of the Fe-bearing calcite lattice relative to the pure calcite. Both reactions are interpreted as fluid-mediated replacement reactions which use the crystallography and elemental chemistry of the calcite. Experiments of fluid-mediated replacement reactions show that they proceed much faster than diffusion-based reactions. This is important when considering the rates of reactions relative to fluid flow in mineralising systems.

Pearce, Mark A.; Timms, Nicholas E.; Hough, Robert M.; Cleverley, James S.

2013-10-01

160

Growth of Prismatic GaN Single Crystals with High Transparency on Small GaN Seed Crystals by Ca-Li-Added Na Flux Method  

NASA Astrophysics Data System (ADS)

The addition of Ca-Li to Na flux was attempted in order to control the growth habit and further improve transparency of GaN crystals. As a result, the growth habit changed to prism shape by the addition of Ca. Furthermore, we succeeded in growing prismatic GaN crystals with high transparency by adding appropriate amounts of Ca and Li to the flux. The optical absorption coefficient at 450 nm wavelength obtained from the crystal was 1.07 cm-1. This result suggests that the addition of Ca-Li to Na flux is a promising method of growing transparent GaN single crystals.

Konishi, Yusuke; Masumoto, Keiko; Murakami, Kosuke; Imabayashi, Hiroki; Takazawa, Hideo; Todoroki, Yuma; Matsuo, Daisuke; Maruyama, Mihoko; Imade, Mamoru; Yoshimura, Masashi; Sasaki, Takatomo; Mori, Yusuke

2012-02-01

161

Calcite dissolution: Effects of trace cations naturally present in Iceland spar calcites  

NASA Astrophysics Data System (ADS)

In situ dissolution experiments on a set of pure, optical quality Iceland spar calcite samples from four different localities showed etch pit step retreat rates to be inversely proportional to total inherent trace cation composition. Atomic absorption spectroscopy (AAS) revealed Fe 2+, Mg 2+, Mn 2+ and Sr 2+ in amounts varying from a few to hundreds of ppm. We used a very simple experimental set-up, with an Atomic Force Microscope (AFM) fluid cell and a droplet of MilliQ water. As the calcite dissolved and approached equilibrium with the solution, trace cations were released, which were then present for interaction with the dissolving surface. We monitored continuous free-drift dissolution, in situ, on fresh {1014} cleavage surfaces for up to 40 min. Dissolution produced one-layer-deep, rhombic etch pits that continually expanded as we collected images. The rhombohedral symmetry of calcite defines two obtuse and two acute edges on the cleavage surface of etch pits and these, as expected from previous work, had different dissolution rates. Despite identical experimental conditions for all samples, we observed lower step retreat rates for both obtuse and acute edges on calcite characterised by relatively high trace cation composition. Increased cation concentration, particularly Mn, was also correlated with rounding of obtuse-obtuse corners, resulting in obtuse step retreat rates similar to those for acute sides. Physcial limitations of the AFM technique were taken into account when measuring step rate retreat and results were collected only from single-layer etch pits, which represent crystalline calcite with minimal defects. Dissolution rates presented here are thus lower than previous reports for studies of deep etch pits and where the physical limitations of imaging may not have been considered. In addition to molecular-level proof that divalent cations inherent at ppm levels in the calcite affect the dissolution process, these results show that pure, optical quality Iceland spar calcite should not be considered pure in the chemical sense. The results imply that dissolution rates determined for ideal systems with pure, synthetic or natural, materials may be considered as the boundary condition for dissolution in real systems in nature, where cations are always present both in the solution and in the initial solid.

Harstad, A. O.; Stipp, S. L. S.

2007-01-01

162

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

NASA Astrophysics Data System (ADS)

Carbonate minerals play an important role in regulating the chemistry of aquatic environments, including the oceans, aquifers, hydrothermal systems, soils and sediments. Through mineral surface processes such as dissolution, precipitation and sorption, carbonate minerals affect the biogeochemical cycles of not only the constituent elements of carbonates, such as Ca, Mg, Fe and C, but also H, P and trace elements. Surface charging of the calcite mineral-water interface, and its reactivity towards foreign ions can be quantified using a surface structural model that includes, among others, the water structure at the interface (i.e. hydrogen bridging) [1,2] in accordance with the CD-MUSIC formalism [3]. Here we will show the impact of foreign metals such as Mg and Sr on the water structure around different surface sites present in etch pits and on growth terraces at the calcite (10-14) surface. We have performed Molecular Dynamics simulations of metal-doped calcite surfaces, using different interatomic water potentials. Results show that the local environment around the structurally distinct sites differs depending on metal presence, suggesting that metal substitutions in calcite affect its reactivity. The information obtained in this study will help in improving existing macroscopic surface model for the reactivity of calcite [2] and give more general insight in mineral surface reactivity in relation to crystal composition. [1] Wolthers, Charlet, & Van Cappellen (2008). Am. J. Sci., 308, 905-941. [2] Wolthers, Di Tommaso, Du, & de Leeuw (2012). Phys. Chem. Chem. Phys. 14, 15145-15157. [3] Hiemstra and Van Riemsdijk (1996) J. Colloid Interf. Sci. 179, 488-508.

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

2014-05-01

163

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

164

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

E-print Network

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

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

2008-01-01

165

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

SciTech Connect

The deformation behavior of calcite has been of longstanding interest. Through experiments on single crystals, deformation mechanisms were established such as mechanical twinning on e = {l_brace}{bar 1}018{r_brace} <40{bar 4}1> in the positive sense and slip on r = {l_brace}10{bar 1}4{r_brace} <20{bar 2}{bar 1}> and f = {l_brace}{bar 1}012{r_brace} <0{bar 2}2{bar 1}> both in the negative sense. More recently it was observed that at higher temperatures f{l_brace}{bar 1}012{r_brace} <10{bar 1}1> slip in both senses becomes active and, based on slip line analysis, it was suggested that e(0001) <11{bar 2}0> slip may occur. So far there had been no direct evidence for basal slip, which is the dominant system in dolomite. With new torsion experiments on calcite single crystals at 900 K and transmission electron microscopy, this study identifies (0001) <11{bar 2}0> slip unambiguously by direct imaging of dislocations and diffraction contrast analysis. Including this slip system in polycrystal plasticity simulations, enigmatic texture patterns observed in compression and torsion of calcite rocks at high temperature can now be explained, resolving a long-standing puzzle.

Barber, D. J.; Wenk, H.-R.; Gomez-Barreiro, J.; Rybacki, E.; Dresen, G. (UCB); (Essex); (GFZ)

2008-06-09

166

The Coordination of Mg in Foraminiferal Calcite  

NASA Astrophysics Data System (ADS)

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).

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

2012-12-01

167

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

168

Emission polarization study on quartz and calcite.  

NASA Technical Reports Server (NTRS)

Calculation of the spectral emission polarization of quartz and calcite polished plates for observation angles of 20 and 70 deg by the substitution of complex index of refraction values for each mineral into Fresnel's equations. The emission polarization is shown to be quite wavelength-dependent, demonstrating that selected narrow or medium-width spectral bands exhibit a significantly higher percentage of polarization than a broad spectral band for these two minerals. Field measurements with a broadband infrared radiometer yield polarizations on the order of 2% for a coarse-grained granite rock and beach sand (both quartz-rich). This implies that a more sensitive detector with a selected medium-width filter may be capable of measuring emission polarization accurately enough to make this parameter useful as a remote sensing tool for discrimination among rocks on the basis of texture.

Vincent, R. K.

1972-01-01

169

Sequestration of Selenium on Calcite Surfaces Revealed by Nanoscale Imaging  

E-print Network

Sequestration of Selenium on Calcite Surfaces Revealed by Nanoscale Imaging Christine V. Putnis structure. Among these elements, selenium is important because of its high toxicity in natural systems and for human health. In the form of selenite (Se(IV) ), selenium can be incorporated into calcite during growth

170

Mg isotope fractionation during calcite precipitation: An experimental study  

NASA Astrophysics Data System (ADS)

Experimental precipitations of calcite and other carbonate minerals were performed under various conditions of pH, temperature and solution Mg/Ca to determine the Mg partition coefficient and Mg isotope fractionation. Fifteen experiments were performed at pH ranging from 7.41 0.07 to 8.51 0.39, temperature ranging from 16.2 0.7 to 26.5 0.3 C and Mg/Casolution ranging from 0.11 to 0.52 mol/mol. The apparent Mg partition coefficient between calcite and solution (DMg) spans a large range of values from 0.018 0.014 to 0.15 0.11 and carbonate Mg isotope fractionation (?26Mg) ranges from -2.53 0.25 to -1.33 0.14 and does not correlate with either pH or temperature. The range in DMg and ?26Mg suggests non-equilibrium partitioning controlled by the processes of calcite growth, i.e. mixing between calcite grown at equilibrium and fluid inclusions, and entrapment of a surface Mg-rich calcite layer in isotopic equilibrium with the solution. The equilibrium Mg isotope fractionation between inorganic calcite and solution is estimated to be -2.13 0.24. Additional Mg elemental and isotopic fractionations are observed to occur during biogenic formation of calcite due to variable removal of Mg by the organisms (high-Mg calcite corals, foraminifera) of seawater Mg from their calcification medium.

Saulnier, Sgolne; Rollion-Bard, Claire; Vigier, Nathalie; Chaussidon, Marc

2012-08-01

171

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

E-print Network

The Bowman-Birk trypsin inhibitor from barley seeds (BBBI) consists of 125 amino acid residues with two to backbone atoms in the core of each domain. One interesting feature of this two-domain inhibitor structure of serine protease inhibitors, which block trypsin and chymotrypsin from animal, fungal, and bacterial

Suh, Se Won

172

crystal  

NASA Astrophysics Data System (ADS)

A Nd3+:Na2La4(WO4)7 crystal with dimensions of ? 17 30 mm3 was grown by the Czochralski method. The thermal expansion coefficients of Nd3+:Na2La4(WO4)7 crystal are 1.32 10-5 K-1 along c-axis and 1.23 10-5 K-1 along a-axis, respectively. The spectroscopic characteristics of Nd3+:Na2La4(WO4)7 crystal were investigated. The Judd-Ofelt theory was applied to calculate the spectral parameters. The absorption cross sections at 805 nm are 2.17 10-20 cm2 with a full width at half maximum (FWHM) of 15 nm for ?-polarization, and 2.29 10-20 cm2 with a FWHM of 14 nm for ?-polarization. The emission cross sections are 3.19 10-20 cm2 for ?-polarization and 2.67 10-20 cm2 for ?-polarization at 1,064 nm. The fluorescence quantum efficiency is 67 %. The quasi-cw laser of Nd3+:Na2La4(WO4)7 crystal was performed. The maximum output power is 80 mW. The slope efficiency is 7.12 %. The results suggest Nd3+:Na2La4(WO4)7 crystal as a promising laser crystal fit for laser diode pumping.

Yu, Yi; Huang, Yisheng; Zhang, Lizhen; Lin, Zhoubin; Sun, Shijia; Wang, Guofu

2014-07-01

173

Organic Surfaces Promote Calcite Nucleation Through Biomolecule-Specific Reductions in Interfacial Free Energy  

NASA Astrophysics Data System (ADS)

Sites of biogenic calcification are comprised of complex macromolecular assemblages that are implicated in regulating the onset of mineralization. Classical nucleation theory predicts that the organic templates provided by these proteins and polysaccharides significantly affect nucleation rate by modulating interfacial free energy, which determines the thermodynamic barrier to nucleation. Recent evidence suggests that calcium carbonate (CaCO3) formation often involves pre-nucleation clusters and transient precursor phases, which raises the question of how biomolecular controls on crystallization are related to emerging concepts in non-classical mineralization. While previous studies qualitatively demonstrate that the chemical functionalities of biomolecules influence the nucleating mineral phase and morphology, a mechanistic understanding of their control over nucleation kinetics and thermodynamics is not well established. Here we test the hypothesis that specific chemical functional groups regulate the kinetics and thermodynamics of CaCO3 formation by using self-assembled monolayers (SAMs) as substrates for calcite nucleation. We measured nucleation rates on substrates with different termini (-COOH, -PO4, and -SH) and alkanethiol chain lengths (16-C and 11-C) at a variety of chemical driving forces, both above and below the reported solubility of amorphous calcium carbonate (ACC). Using classical nucleation theory to interpret the kinetic data, we calculated calcite-substrate interfacial energies and estimated substrate-specific effects on the thermodynamic barrier to nucleation. Calcite - substrate interaction forces were quantified with independent dynamic force spectroscopy (DFS) measurements. The nucleation rate measurements show that organic templates reduce the thermodynamic barrier to calcite nucleation compared to homogeneous nucleation through reductions in interfacial free energy. These free energies are correlated with independent DFS measurements of calcite-substrate interaction force by a systematic relationship that is general to chemistry and chain length. Calcite nucleation in these systems is accurately described with classical models of nucleation. The findings demonstrate a physical basis for how organic surfaces reduce the thermodynamic barrier to nucleation and show that precursor phases and pre-nucleation clusters are not required for template-directed mineralization.

Hamm, L. M.; Han, N.; Giuffre, A. J.; De Yoreo, J.; Dove, P. M.

2012-12-01

174

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

NASA Astrophysics Data System (ADS)

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 10-10s-1 and for the marble host rock around 10-12s-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.

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

2014-12-01

175

Effect of calcite on lead-rich cementitious solid waste forms  

SciTech Connect

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

Lee, Dongjin [School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); Swarbrick, Gareth [School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); Waite, T. David [School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia)]. E-mail: D.waite@unsw.edu.au

2005-06-01

176

crystal  

NASA Astrophysics Data System (ADS)

The polarized absorption, emission spectra and decay time measurements of Pr3+-doped CaYAlO4 single crystal have been performed at room temperature. Based on the Judd-Ofelt theory, the spectroscopic parameters , radiative transition probabilities, radiative lifetimes and branching ratios were obtained. The stimulated emission cross-section, fluorescence lifetimes and the quantum efficiency of the promising laser transition were also calculated and compared with other reported crystals. The results show that Pr3+:CaYAlO4 is a promising candidate for visible solid-state laser emission.

Lv, Shaozhen; Wang, Yan; Zhu, Zhaojie; You, Zhenyu; Li, Jianfu; Gao, Shufang; Wang, Hongyan; Tu, Chaoyang

2014-07-01

177

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

SciTech Connect

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.

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

178

Quantifying Surface Kinetic Fractionations for Isotopes and Trace Elements in Calcite Precipitated from Aqueous Solution  

NASA Astrophysics Data System (ADS)

The isotopic ratios and trace element concentrations in calcite and other carbonate minerals form the basis for several paleoenvironmental indicators that are relied upon to reconstruct past Earth climates and ocean processes. Most of these carbonate minerals form at low temperatures (0 to 30C) and consequently are unlikely to have precipitated from aqueous solutions at equilibrium. The non-equilibrium nature of the precipitation process is well illustrated by the experimentally demonstrated precipitation rate-dependence of parameters such as the Ca and O isotopic composition, and the Sr, Mg, and Mn concentrations of calcite. We have been focused on understanding how to predict the magnitude and controls on these kinetic effects using a general transition-state theory approach, as well as models of ion-by-ion growth, molecular dynamics simulations of the desolvation step required for addition of cations to a mineral surface, and further experiments that involve carefully controlled solution compositions and crystal growth rates. Although models have been proposed that invoke diffusion as the primary control on the non-equilibrium aspects of calcite precipitation, it is relatively easy to show that diffusion is not likely to be the primary controlling process. We have focused on understanding the kinetic effects operating at and near the mineral surface, which are undeniably present and important, and appear to be of the correct magnitude and direction to account for observations in both laboratory and natural calcites. The approach we are using is also applicable to higher temperature aqueous precipitation. There are indications from Ca isotopes that similar surface kinetic effects occur at temperatures of 300 to 400C. Kinetic isotope and trace element effects are critically dependent on molecular exchange rates between the mineral surface and the aqueous solution, and the ratio of these rates to the net crystal growth rate. The challenge is to predict and/or measure these rates, which are dependent in a complex fashion on solution saturation state, cation/anion ratios, ionic strength, and other aspects of solution composition. In effect, trace elements and isotopes can provide a measure of these rates, and the derived rates from available experimental data are broadly compatible with measured calcite dissolution and precipitation rates and their dependence on solution composition. Overall, it appears possible to develop a comprehensive framework for understanding kinetic trace element and isotopic fractionation effects during precipitation of minerals from aqueous solution, and to constrain the important controlling parameters using a combination of experiments and simulations.

DePaolo, D. J.; Nielsen, L. C.; Hofmann, A. E.; DeYoreo, J.; Gagnon, A. C.; Watkins, J. M.; Ryerson, F. J.; Brown, S. T.

2011-12-01

179

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

PubMed Central

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

Rusznyak, Anna; Akob, Denise M.; Nietzsche, Sandor; Eusterhues, Karin; Totsche, Kai Uwe; Neu, Thomas R.; Frosch, Torsten; Popp, Jurgen; Keiner, Robert; Geletneky, Jorn; Katzschmann, Lutz; Schulze, Ernst-Detlef

2012-01-01

180

Calcite biomineralization by bacterial isolates from the recently discovered pristine karstic herrenberg cave.  

PubMed

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

Rusznyk, Anna; Akob, Denise M; Nietzsche, Sndor; Eusterhues, Karin; Totsche, Kai Uwe; Neu, Thomas R; Frosch, Torsten; Popp, Jrgen; Keiner, Robert; Geletneky, Jrn; Katzschmann, Lutz; Schulze, Ernst-Detlef; Ksel, Kirsten

2012-02-01

181

Frictional Properties and Microstructure of Calcite-Rich Fault Gouges Sheared at Sub-Seismic Sliding Velocities  

NASA Astrophysics Data System (ADS)

We report an experimental and microstructural study of the frictional properties of simulated fault gouges prepared from natural limestone (96 % CaCO3) and pure calcite. Our experiments consisted of direct shear tests performed, under dry and wet conditions, at an effective normal stress of 50 MPa, at 18-150 C and sliding velocities of 0.1-10 ?m/s. Wet experiments used a pore water pressure of 10 MPa. Wet gouges typically showed a lower steady-state frictional strength (? = 0.6) than dry gouges (? = 0.7-0.8), particularly in the case of the pure calcite samples. All runs showed a transition from stable velocity strengthening to (potentially) unstable velocity weakening slip above 80-100 C. All recovered samples showed patchy, mirror-like surfaces marking boundary shear planes. Optical study of sections cut normal to the shear plane and parallel to the shear direction showed both boundary and inclined shear bands, characterized by extreme grain comminution and a crystallographic preferred orientation. Cross-sections of boundary shears, cut normal to the shear direction using focused ion beamSEM, from pure calcite gouges sheared at 18 and 150 C, revealed dense arrays of rounded, ~0.3 ?m-sized particles in the shear band core. Transmission electron microscopy showed that these particles consist of 5-20 nm sized calcite nanocrystals. All samples showed evidence for cataclasis and crystal plasticity. Comparing our results with previous models for gouge friction, we suggest that frictional behaviour was controlled by competition between crystal plastic and granular flow processes active in the shear bands, with water facilitating pressure solution, subcritical cracking and intergranular lubrication. Our data have important implications for the depth of the seismogenic zone in tectonically active limestone terrains. Contrary to recent claims, our data also demonstrate that nanocrystalline mirror-like slip surfaces in calcite(-rich) faults are not necessarily indicative of seismic slip rates.

Verberne, B. A.; Spiers, C. J.; Niemeijer, A. R.; De Bresser, J. H. P.; De Winter, D. A. M.; Plmper, O.

2013-12-01

182

Low latitude (12N) climate signatures preserved in the stable isotope composition of soil phyllosilicate and calcite, northwestern Ethiopia, Africa  

NASA Astrophysics Data System (ADS)

The mineralogical, chemical, oxygen and hydrogen-isotope composition of the <0.2?m size fraction of phyllosilicates and coexisting calcite are presented from four modern soil profiles developed upon fluvial terraces of the Shinfa River (lowlands of northwestern Ethiopia). The <0.2?m size fraction of most soils is dominated by smectite, with varying amounts of kaolinite. Mineralogical and chemical data were used to calculate oxygen and hydrogen fractionation factors for each phyllosilicate mixture. These fractionation factors were used in conjunction with measured ?18O and ?D values to calculate phyllosilicate crystallization temperatures as well as the oxygen isotope composition of soil water from which the phyllosilicates formed. Measured ?18OV-SMOW and ?DV-SMOW values of the phyllosilicates range from 22.1 to 26.7, and -42 to -35, respectively and correspond to a range of crystallization temperatures from 25 3C to 33 3C. Equilibrium soil water ?18O values range from -1.9 to +2.0. The average ?18OV-SMOW values of coexisting soil calcite range from 28.3 to 29.9. Estimates of soil water ?18O values from the phyllosilicates in conjunction with calcite ?18O values correspond to calcite crystallization temperatures that range from 25 to 32C, likely indicating chemical equilibrium between these two soil minerals. Shinfa River water ?18OV-SMOW are highly variable, as a result of extreme seasonality and evaporation, ranging from approximately -2 during the rainy season. to +20 during the dry season. Comparison of calculated soil water ?18O values with Shinfa River water ?18O values suggest that pedogenic phyllosilicates and calcite preserve a record of the oxygen isotopic composition of local meteoric waters that fall during the wet, summer months (June-September). The local variations in calculated temperatures of phyllosilicate and calcite crystallization among terraces appear to correlate with extent of canopy cover at each sight. Specifically, the lowest calculated temperature of 25C is associated with an open woodland environment with ~20-30% canopy cover, while the highest calculated temperatures (i.e., 30 to 33C) are associated with actively cultivated sights that have little, or no, canopy cover. These results emphasize the point that chemical equilibrium may exist between soil minerals, but they need not preserve isotopic information about mean annual conditions.

Rosenau, N. A.; Tabor, N. J.; Myers, T. S.; Kappelman, J.

2012-12-01

183

Distinguishing between natural and recarbonated calcite in oil shale ashes  

Microsoft Academic Search

Oil shale ashes from the PAMA demonstration power plant in the Negev region of Israel are produced by fluidized bed combustion\\u000a (700850C) under short residence time. The FED is organic-rich calcareous raw material rich in carbonate rather than clays.\\u000a Thus it is important to ascertain whether the calcite in the ashes is original natural calcite from the raw material or

S. Shoval; O. Yofe; Y. Nathan

2003-01-01

184

Pomegranate seeds  

NSDL National Science Digital Library

This pomegranate has many seeds inside. These seeds are surrounded individually by red fruit. Some fruits also have many seeds, but all of the seeds are surrounded by the fruit instead of individually, like in an apple.

Peter N/A (None;)

2005-01-01

185

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

NASA Technical Reports Server (NTRS)

The shock behavior of calcite and gypsum is important in understanding the Cretaceous/Tertiary event and other terrestrial impacts that contain evaporite sediments in their targets. Most interest focuses on issues of devolatilization to quantify the production of CO2 or SO2 to better understand their role in generating a temporary atmosphere and its effects on climate and biota [e.g., papers in 1,2,3,4]. Devolatilization of carbonate is also important because the dispersion and fragmentation of ejecta is strongly controlled by the expansion of large volumes of gas during the impact process as well [5,6]. Shock recovery experiments for calcite yield seemingly conflicting results: early experimental devolatilization studies [7,8,9] suggested that calcite was substantially outgassed at 30 GPa (> 50%). However, the recent petrographic work of [10,11,12] presented evidence that essentially intact calcite is recovered from 60 GPa experiments. [13] reported results of shock experiments on anhydrite, gypsum, and mixtures of those phases with silica. Their observations indicate little or no devolatilization of anhydrite shocked to 42 GPa and that the fraction of sulfur, by mass, that degassed is approx.10(exp -2) of theoretical prediction. In another (preliminary) report of shock experiments on calcite, anhydrite, and gypsum, [14] observe calcite recrystallization when shock loaded at 61 GPa, only intensive plastic deformation in anhydrite shock loaded at 63 GPa, and gypsum converted to anhydrite when shock loaded at 56 GPa. [15] shock loaded anhydrite and quartz to a peak pressure of 60 GPa. All of the quartz grains were trans-formed to glass and the platy anhydrite grains were completely pseudomorphed by small crystallized anhydrite grains. However, no evidence of interaction between the two phases could be observed and they suggest that recrystallization of anhydrite grains is the result of a solid state transformation. [16] reanalyzed the calcite and anhydrite shock wave experiments of [17] using improved equations of state of porous materials and vaporized products. They determined the pressures for incipient and complete vaporization to be 32.5 and 122 GPa for anhydrite and 17.8 and 54.1 GPa for calcite, respectively, a factor of 2 to 3 lower than reported earlier by [17].

Bell, Mary S.

2009-01-01

186

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

187

Complete subsite mapping of a "loopful" GH19 chitinase from rye seeds based on its crystal structure.  

PubMed

Crystallographic analysis of a mutated form of "loopful" GH19 chitinase from rye seeds a double mutant RSC-c, in which Glu67 and Trp72 are mutated to glutamine and alanine, respectively, (RSC-c-E67Q/W72A) in complex with chitin tetrasaccharide (GlcNAc)? revealed that the entire substrate-binding cleft was completely occupied with the sugar residues of two (GlcNAc)? molecules. One (GlcNAc)? molecule bound to subsites -4 to -1, while the other bound to subsites +1 to +4. Comparisons of the main chain conformation between liganded RSC-c-E67Q/W72A and unliganded wild type RSC-c suggested domain motion essential for catalysis. This is the first report on the complete subsite mapping of GH19 chitinase. PMID:23871710

Ohnuma, Takayuki; Umemoto, Naoyuki; Kondo, Kaori; Numata, Tomoyuki; Fukamizo, Tamo

2013-08-19

188

Effect of current-season application of calcitic lime and phosphorus fertilization on soil pH, potato growth, yield, dry matter content, and cadmium concentration  

Microsoft Academic Search

Two glasshouse and three field experiments were conducted to investigate the effects of current-season application of calcitic lime and phosphorus (P) fertilizer on (i) soil pHw, (ii) growth of haulms (tops), (iii) tuber number, yield and dry matter content, and (iv) cadmium (Cd) concentrations in tubers of the potato (Solanum tuberosum L.) cultivars Russet Burbank, Crystal, and Pontiac grown in

N. A. Maier; M. J. McLaughlin; M. Heap; M. Butt; M. K. Smart

2002-01-01

189

doi:10.1016/j.gca.2005.04.006 Effects of temperature and transport conditions on calcite growth in the presence of Mg2  

E-print Network

doi:10.1016/j.gca.2005.04.006 Effects of temperature and transport conditions on calcite growth-spatial-resolution analysis of Mg contents in experimental crystals, with particular attention to the effects of temperature precisely measured with fluid cell atomic force microscopy over a range of temperatures, degrees

Dove, Patricia M.

190

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

NASA Astrophysics Data System (ADS)

We present a cylindrically curved GaAs x-ray spectrometer with energy resolution ?E/E = 1.1 10-4 and wave-number resolution of ?k/k = 3 10-3, allowing plasmon scattering at the resolution limits of the Linac Coherent Light Source (LCLS) x-ray free-electron laser. It spans scattering wavenumbers of 3.6 to 5.2/ 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.

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

2014-09-01

191

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

PubMed

We present a cylindrically curved GaAs x-ray spectrometer with energy resolution ?E/E = 1.1 ?10(-4) and wave-number resolution of ?k/k = 3 ?10(-3), allowing plasmon scattering at the resolution limits of the Linac Coherent Light Source (LCLS) x-ray free-electron laser. It spans scattering wavenumbers of 3.6 to 5.2/ 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. PMID:25273706

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

2014-09-01

192

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

E-print Network

We present a cylindrically curved GaAs x-ray spectrometer with energy resolution $\\Delta E/E = 1.1\\cdot 10^{-4}$ and wave-number resolution of $\\Delta k/k = 3\\cdot 10^{-3}$, allowing plasmon scattering at the resolution limits of the Linac Coherent Light Source (LCLS) x-ray free-electron laser. It spans scattering wavenumbers of 3.6 to $5.2/$\\AA\\ in 100 separate bins, with only 0.34\\% wavenumber blurring. The dispersion of 0.418~eV/$13.5\\,\\mu$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 HAPG 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.

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

2014-01-01

193

Calcite and Picocyanobacteria in Lakes: Factors Affecting Their Interaction  

NASA Astrophysics Data System (ADS)

Calcites build large deposits which have been observed in the rock record throughout geological time at various localities around the globe. Carbonate deposits have affected atmospheric carbon dioxide concentration. As it has been generally accepted, inorganic precipitation represents a source of carbon dioxide on short geological time scales and a sink of inorganic carbon at long time scales from millions to thousands of millions years. However, recent research indicates that calcite deposits may result from microbial calcification instead of inorganic precipitation. In this case the process may reduce atmospheric carbon dioxide on geologically short time scales. Thus the effect of carbonate sediment deposition on global carbon cycling depends on the origin of carbonate. Thus it is essential to understand the cause and the key parameters affecting calcite precipitation. The role of algae and bacteria in calcite formation in lakes has not been evaluated in detail. Some evidence, however, exists supporting precipitation of calcium carbonate by microbes as the origin of whiting. Several field studies on lakes have also produced puzzling results: The peaks of algal blooms were often not found at the same time as precipitation events of calcite. We suspect that parts of the discrepancies in the interpretation of field observations are due to the activity of autotrophic picoplankton. The unicellular autotrophic picoplankton (APP) is a ubiquitous component of pelagic ecosystems. But it has often been overlooked due to its small cell size of 0.2 - 2 ? m in diameter. Coccoid picocyanobacteria of the Synechococcus-type dominate the picoplankton community in most oligotrophic systems. Recently, laboratory experiments and field observations suggested that APP may play an important role in calcite precipitation. The aim of this study was to examine the influence of environmental factors such as saturation state, concentration of different dissolved ions and characteristics of the surface of cells on interaction between calcite and picocyanobacteria under both laboratory and field conditions. Laboratory experiments were performed with a picocyanobacteria strain Synechococcus-type. Using ion selective electrodes we monitored calcite precipitation induced by bacteria in the solutions of a different composition (calcium 0.7 - 48 mM, inorganic carbonate 6 - 35 ? M). Electron and atomic force microscopy measurements provided insight into the cell-mineral interface. Furthermore, quantitative investigations of the types and densities of proton binding sites on a bacterial surface will be reported from the acid-base titrations on bacteria. Results of these initial experiments are encouraging and demonstrate by direct measurements the potential of picocyanobacteria to precipitate calcite. The amount of the precipitated calcite varied in experiments with a different ratio of dissolved inorganic carbon and calcium. The microscopic observations provide some evidence that the cell walls of cyanobacteria act as a substrate of nucleation of calcite. Temporal and spatial correlations of cyanobacteria and calcite, as well as images of bacterial shape particles indicated that picoplankton plays an important role in calcite precipitation in Lake Lucerne. This class of phytoplankton has to be considered in studying the biogeochemical cycling of oligotrophic hardwater lakes.

Dittrich, M.; Obst, M.; Mavrocordatos, D.

2003-12-01

194

Uranyl Incorporation in Organic-Bearing Soil Calcite  

NASA Astrophysics Data System (ADS)

Phosphor imaging and fission track maps reveal a close correlation between uranium and organic-rich calcite that lines roots in an ancient caliche soil. Concordant U-Pb ages show that this uranium has not been mobilized since the soil calcite formed 298 1 Ma ago. Luminescence spectroscopic analysis of the organic-rich calcite demonstrates that uranium is present in the oxidized state. More or less comparable luminescence spectra were collected using a CW lamp at room temperature and at liquid nitrogen (LN2) temperature. Spectra for inorganic U species are generally greatly enhanced at liquid nitrogen temperatures over room temperature and thus the similarity may suggest that the U is bound to organic matter. UV-excitation Raman spectroscopy of the calcite samples reveals a vibrational signature that is, in addition to the calcite peaks, essentially identical to that of sodium humate, acquired under similar conditions and consistent with those reported previously for humate substances. Since these spectra are dominated by the carbon backbone structure, the persistence of a carbon backbone structure is noted, but persistence of the ligating functional groups cannot be proven directly. We suggest that this sample records a snapshot of the process of uranium complexation with organic acids in natural systems. In our model organic acids with active functional groups that complex uranyl are sorbed onto the calcite surface and then incorporated as humate into the mineral with further calcite precipitation. Further, the uranyl complex is preserved through near-surface reducing conditions and temperatures to the conditions associated with 2700 meters burial depths. These combined observations suggest that the encapsulating calcite not only prevents reduction of uranium in the surface environment, but also inhibits the breakdown of the humate with burial. Due to the long time scale of immobilization of uranium, evidenced by the age of the calcite, this study has profound implications for understanding sampling for U-series and U-Pb dating of carbonates as well as for developing strategies for nuclear waste management. This study also has implications for any other deposits where uranium is associated with organic matter.

Rasbury, E.; Tait, C.; Donohoe, R. J.

2003-12-01

195

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

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

196

Calcite veins in northeastern Puente Hills, southern California  

SciTech Connect

Calcite vein fillings are locally exposed in the northeastern Puente Hills, 2 mi southwest of Pomona on the northeast margin of the Los Angeles basin. They occur within northeast- and northwest-trending faults in the middle Miocene Glendora Volcanics and in the Soquel Member of the upper Miocene Puente Formation. The veins range in width from 1 in. to 15 ft, and several can be traced hundreds of feet. The veins exhibit complex banded and brecciated textures and emit a strong hydrocarbon odor when broken. The carbon isotopic composition is light (delta/sup 13/C = -22.1 to -45.6 per thousand PDB). The range of the oxygen isotopic composition (delta/sup 18/O = +21.3 to +31.1 per thousand SMOW) generally compares with those reported for diagenetic carbonates in marine Miocene shales of California and Oregon. Dissolution of unusual local Soquel marine carbonates, now primarily dolomite, and diagenetic cements seems to be the most likely source of the calcite that was deposited incrementally along faults to form the calcite-filled veins. The extremely depleted carbon isotope values represent the addition of carbon derived from the chemical and/or biological oxidation of methane; a petroleum source of the methane is suggested by the presence of solid hydrocarbon inclusions in the vein calcite. The formation temperature of the vein calcite was probably below hydrothermal.

Spira, M.O.; Zenger, D.H.

1986-04-01

197

Aragonite and magnesian calcite fluxes to the deep Sargasso Sea  

NASA Astrophysics Data System (ADS)

Aragonite and magnesium calcite fluxes were estimated from a 14-month series of sediment trap samples from depths of 500, 1500 and 3200 m in the Sargasso Sea. No significant difference with depth was observed in fluxes of either carbonate phase. At 3200 m, the mean aragonite flux was 2.8 mg m -2 day -1, or 13% of the total CaCO 3 flux. At all depths pteropods were the major source of aragonite, contributing more carbonate than heteropods by a factor of 3-24. Most of the pteropod aragonite occurred in the size fraction >0.5 mm. At 3200 m, more than half of the pteropod mass flux in the size fraction >0.5 mm comprised four species: Styliola subula, Clio pyramidata, Limacina inflata and Cuvierina columnella. The mean magnesian calcite flux at 3200 m was 1.7 mg m -2 day -1, or 8% of the total CaCO 3 flux. The majority of the magnesian calcite (9-12 mole % MgCO 3) occurred in the finest size fraction. <37 ?m. Evidence suggests that bryozoans attached to floating Sargassum are the source of this magnesian calcite. The combined fluxes of aragonite and magnesian calcite accounted for 21-25% of the mean annual CaCO 3 flux to 1500 and 3200 m.

Fabry, Victoria J.; Deuser, Werner G.

1991-06-01

198

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

PubMed Central

Although crystalline silicon is widely used as substrate material for solar cell, many defects occur during crystal growth. In this study, the generation of crystalline defects in silicon substrates was evaluated. The distributions of small-angle grain boundaries were observed in substrates sliced parallel to the growth direction. Many precipitates consisting of light elemental impurities and small-angle grain boundaries were confirmed to propagate. The precipitates mainly consisted of Si, C, and N atoms. The small-angle grain boundaries were distributed after the precipitation density increased. Then, precipitates appeared at the small-angle grain boundaries. We consider that the origin of the small-angle grain boundaries was lattice mismatch and/or strain caused by the high-density precipitation. PMID:22536006

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

2012-01-01

199

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

NASA Astrophysics Data System (ADS)

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 51C), 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 <35C 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.

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

2012-12-01

200

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

SciTech Connect

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)].

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

201

crystals  

NASA Astrophysics Data System (ADS)

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.

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

2014-07-01

202

Chemistry and kinetics of calcite dissolution in passive treatment systems  

SciTech Connect

Reaction of calcite with AMD is a key remediation process in anoxic limestone drains, (ALD), SAPS, and many wetlands, but predictions of effluent quality are currently based mainly on rules of thumb and prior experience. The PHREEQC computer program can be used to calculate the progress of this and similar reactions, and aid in understanding, design and evaluation of these systems. At pH values less than 5, calcite dissolution rates are strongly influenced by transport parameters such as flow velocity. Estimated calcite dissolution rates from ALD's and column experiments indicate little change in rate with pH, in contrast to published data for well stirred lab experiments. The dissolution rate is affected by concentration of SO{sub 4}, Fe, Al, Ca, P, and other trace solutes. The optimum contact time and sizing of ALD's will be dependent on these and possibly other parameters. Additional experiments are needed to evaluate these dependencies.

Rose, A.W.

1999-07-01

203

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

PubMed Central

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

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

2013-01-01

204

Arsenic removal by gypsum and calcite in lacustrine environments  

NASA Astrophysics Data System (ADS)

After the closure of the coal mining activities in the Massif Central range, France, several lakes were formed as a consequence of mine collapse. The old mines, located at the bottom of lakes, are certified sources of As and heavy metals. During a time period of one year, we have monitored the water column of one of these lakes in order to identify geochemical process controlling water quality dominated by precipitation of gypsum and calcite. We have therefore performed laboratory experiments to study how As is trapped during calcite and gypsurn precipitation in presence of As III and V respectively.

Roman-Ross, G.; Charlet, L.; Cuello, G. J.; Tisserand, D.

2003-05-01

205

On the Formation and Functions of High and Very High Magnesium Calcites in the Continuously Growing Teeth of the Echinoderm Lytechinus variegatus: Development of Crystallinity and Protein Involvement  

PubMed Central

Sea urchin teeth grow continuously and develop a complex mineralized structure consisting of spatially separate but crystallographically aligned first stage calcitic elements of high Mg content (515 mol% mineral). These become cemented together by epitaxially oriented second stage very high Mg calcite (3040 mol% mineral). In the tooth plumula, ingressing preodontoblasts create layered cellular syncytia. Mineral deposits develop within membrane-bound compartments between cellular syncytial layers. We seek to understand how this complex tooth architecture is developed, how individual crystalline calcitic elements become crystallographically aligned, and how their Mg composition is regulated. Synchrotron microbeam X-ray scattering was performed on live, freshly dissected teeth. We observed that the initial diffracting crystals lie within independent syncytial spaces in the plumula. These diffraction patterns match those of mature tooth calcite. Thus, the spatially separate crystallites grow with the same crystallographic orientation seen in the mature tooth. Mineral-related proteins from regions with differing Mg contents were isolated, sequenced, and characterized. A tooth cDNA library was constructed, and selected matrix-related proteins were cloned. Antibodies were prepared and used for immunolocaliztion. Matrix-related proteins are acidic, phosphorylated, and associated with the syncytial membranes. Time-of-flight secondary ion mass spectroscopy of various crystal elements shows unique amino acid, Mg, and Ca ion distributions. High and very high Mg calcites differ in Asp content. Matrix-related proteins are phosphorylated. Very high Mg calcite is associated with Asp-rich protein, and it is restricted to the second stage mineral. Thus, the composition at each part of the tooth is related to architecture and function. PMID:21555859

Veis, Arthur; Stock, Stuart R.; Alvares, Keith; Lux, Elizabeth

2011-01-01

206

Element partitioning in calcite as a function of solution flow rate: a study on vein calcites from the Harz Mountains  

NASA Astrophysics Data System (ADS)

A semi-empirical treatment of isothermal element partitioning caused by flow rate-dependent calcite growth from hydrothermal solutions yields element/Ca ratios that are qualitatively similar to those observed in calcite bands of the Pb-Zn banded ores from the Harz Mountains, Germany. The comparison of the calculations with the analytical results suggests that flow rates varied between episodes of calcite precipitation as well as during formation of individual bands. Based on a flow rate-dependent element partition coefficient, changing element/Ca ratios in precipitates from a hydrotherm are therefore not necessarily indicative of changing compositions of the fluid. The variations in element/Ca ratios to be envisaged could be as much as a factor of three.

Mller, P.; Lders, V.; Schrder, J.; Luck, J.

1991-07-01

207

A data-driven model of the global calcite lysocline  

Microsoft Academic Search

Gridded maps of sediment calcium carbonate (calcite) concentration and overlying water saturation state [Archer, 1996] are combined with maps of benthic oxygen fluxes and sediment accumulation rates from Jahnke [1996] and Cweink [1986] to drive a diagenetic model of calcium carbonate preservation in deep-sea sediments. The only model input for which we cannot draw a detailed map is the rain

David Archer

1996-01-01

208

Calcite veins in northeastern Puente Hills, southern California  

Microsoft Academic Search

Calcite vein fillings are locally exposed in the northeastern Puente Hills, 2 mi southwest of Pomona on the northeast margin of the Los Angeles basin. They occur within northeast- and northwest-trending faults in the middle Miocene Glendora Volcanics and in the Soquel Member of the upper Miocene Puente Formation. The veins range in width from 1 in. to 15 ft,

M. O. Spira; D. H. Zenger

1986-01-01

209

Thermoluminescence measurements of a calcite shell for dating  

NASA Astrophysics Data System (ADS)

For thermoluminescence (TL)-dating of fossil calcite shells of Pecten, a new procedure is introduced. A supralinear function fitted to the 'first-glow growth' of the fossil shell makes it possible to evaluate the natural dose. From the natural doses obtained, we can estimate TL ages of fossil shells from about 5 10 5 years ago to more recently.

Ninagawa, Kiyotaka; Takahashi, Nobusuke; Wada, Tomonori; Yamamoto, Isao; Yamashita, Nobuhiko; Yamashita, Yoshihiko

210

Field Test of Combination Seeding Flares  

E-print Network

2008 during the Polarimetric Cloud Analysis and Seeding Test 2 (POLCAST2) field project. Aircraft for cloud seeding and airborne measurements. For the 1 July 2008 flight, the Cessna 340 aircraft's flareField Test of Combination Seeding Flares Report to Ice Crystal Engineering 5985 49th St. SE

Delene, David J.

211

Temperature limits for preservation of primary calcite clumped isotope paleotemperatures  

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

212

The behavior of Ni 2+ on calcite surfaces  

NASA Astrophysics Data System (ADS)

Transport of Ni 2+ in the geosphere plays a role in the formation of ore deposits as well as in the dispersion of contaminants in the environment. Some elements (Cd 2+, Zn 2+, Na +, K +, and Cl -) are known to diffuse in calcite at the rate of nanometers in months, so questions arose about the ability of Ni 2+ to move away from adsorption sites at the surface into the bulk. Nickel incorporation into calcite is limited by its high dehydration enthalpy and by its ligand field hindrance to entering the distorted octahedra of calcite, but evidence exists that calcite can tolerate several percent Ni 2+ in the structure. Cleaved samples of Iceland spar were exposed for 1 minute to solutions of 10 -3 M and 10 -2 M Ni(ClO 4) 2, the solution was physically removed and the samples were examined using the surface sensitive techniques: X-ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS) and Atomic Force Microscopy (AFM). XPS and TOF-SIMS showed that Ni 2+ was adsorbed while AFM confirmed that dissolution was taking place. The sample was stored in air and relative surface concentration and physical morphology were monitored for 2 years. Trends in the chemical data suggested statistically significant loss of surface Ni 2+ with time, but the decrease was very close to the limits for significance. AFM images demonstrated that surface topography of the Ni-exposed samples is modified by spontaneous recrystalization in the water layer adsorbed from air in exactly the same way that clean calcite surfaces typically rearrange. This process could bury a small amount of Ni 2+ in the bulk, explaining the very weak loss. Limited burial of Ni 2+ within the near-surface could renew calcite adsorption sites, thus increasing uptake capacity. Evidence indicates that surface recrystalization occurs even in very dry environments (<5% humidity). This means that burial could play a role in Ni 2+ mobility in unsaturated groundwater regimes or in fractures (such as in concrete) where water flow is intermittent. An important point is, however, in comparison to incorporation rates for divalent Cd and Zn, the extent of movement of Ni 2+ is extremely low. Thus, incorporation might have an effect on Ni 2+ retardation in flow paths extending over very long time scales (>10,000 years) such as would be relevant for geological processes and for long-term radioactive waste disposal. However, incorporation by burial would have negligible effect on the amount of Ni 2+ removed from groundwater by adsorption, in systems where the transport times are short (<100 years) such as for drinking water supplies from calcite-bearing porous media.

Hoffmann, U.; Stipp, S. L. S.

2001-11-01

213

Reconstructing Cambro-Ordovician Seawater Composition using Clumped Isotope Paleothermometry on Calcitic and Phosphatic Brachiopods  

NASA Astrophysics Data System (ADS)

A secular increase in ?18O values of marine fossils through early Phanerozoic time raises questions about the evolution of climate and the water cycle. This pattern suggests two end-member hypotheses 1) surface temperatures during early Paleozoic time were very warm, in excess of 40C (tropical MAT), or 2) the isotopic composition of seawater increased by up to 7-8. It has been difficult to evaluate these hypotheses because the ?18O composition of fossils depends on both temperature and the ?18O of water. Furthermore, primary isotopic signatures can be overprinted by diagenetic processes that modify geological materials. This too could explain the decrease in ?18O values of marine fossils with age. Carbonate clumped isotope thermometry can constrain this problem by providing an independent measure of crystallization temperature and, when paired with classical ?18O paleothermometry, can determine the isotopic composition of the fluid the mineral last equilibrated with. Combined with traditional tools, this method has the potential to untangle primary isotopic signatures from diagenetic signals. We measured the isotopic ordering of CO3 groups (?47) substituted into the phosphate lattice of phosphatic brachiopods in Cambrian strata. Phosphatic fossils are generally less soluble than carbonates in surface and diagenetic environments, and so are hypothesized to provide a more robust record of primary growth conditions. They also provide an archive prior to the rise of thick shelled calcitic fossils during the Ordovician Radiation. Additionally, measurements of the ?18O of the CO3 groups can be compared with the ?18O of PO4 groups to test whether their mutual fractionation is consistent with primary growth and the apparent temperature recorded by carbonate clumped isotope measurements. We are constructing a phosphatic brachiopod calibration for carbonate clumped isotope thermometry, and ?47 values of CO2 extracted from modern phosphatic brachiopods suggest they faithfully record seawater temperatures following a calibration similar to the canonical calcite clumped isotope thermometer. Samples from Japan yield a temperature of 231.5C (1 SD) and ?18O water composition of 0.20.5 VSMOW (calculated assuming CO3 groups have fractionations with respect to water equal to that of calcite). Nine samples of calcitic brachiopods from the 455 Ma Ordovician Decorah Formation yield a mean temperature of 363C and a ?18Owater composition of -0.71 VSMOW, excluding three brachiopods with temperatures in the low 40s. Four measurements of well-preserved phosphatic brachiopods from the 500 Ma Eau Claire Formation yield a mean temperature of 343C and a ?18Owater composition of -3.31 VSMOW. The ?18O measurements of PO4 groups from the brachiopods suggest similar water compositions based on equilibrium precipitation at 34C (Pucat et al., 2010). These results constrain the climate and potential variation in ?18O of seawater during the early Paleozoic, suggesting that shallow tropical marine environments were somewhat warmer than today, but less so than some predicted (e.g. Trotter et al., 2008). Future measurements of phosphatic brachiopods from the Decorah Formation and modern phosphatic and calcitic brachiopods from a range of environments will provide a direct comparison of the calcitic and phosphatic record.

Bergmann, K.; Robles, M.; Finnegan, S.; Hughes, N. C.; Eiler, J. M.; Fischer, W. W.

2012-12-01

214

Molecular models of a hydrated calcite mineral surface  

NASA Astrophysics Data System (ADS)

Hydrated mineral surfaces play an important role in many processes in biological, geological, and industrial applications. An energy force field was developed for molecular mechanics and molecular dynamics simulations of hydrated carbonate minerals and was applied to investigate the behavior of water on the (1014) calcite surface. The force field is a significant development for large-scale molecular simulations of these systems, and provides good agreement with experimental and previous modeling results. Simulations indicate that water molecules are significantly ordered near the calcite surface. The predominant surface configuration (75-80%) results from coordination of a water molecule with a single calcium cation-carbonate anion pair, while the less common situation involves water coordination with two ion pairs. Surface restructuring and variation in coordination in the water layers results in distinct distances for water oxygens above the calcite surfacea two-component first monolayer (2.3 and 3.0 ) and a secondary monolayer (5.0 ). The different coordinations also alter lateral displacement, hydrogen bonding, and surface-normal orientation of the water molecules. The ordering of water molecules and the formation of a unique hydrogen bonding network at the calcite surface influence the physical properties of the interfacial water. Surface exchange of water molecules is observed by molecular dynamics simulation to occur at a rate of one exchange per 10 ps. Diffusion coefficients derived from mean square displacement analysis of atomic trajectories indicate a dependence of water transport based on the distance of the water molecules from the calcite surface.

Perry, Thomas D.; Cygan, Randall T.; Mitchell, Ralph

2007-12-01

215

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

NASA Astrophysics Data System (ADS)

Carbonate minerals in CM carbonaceous chondrite meteorites, along with the silicates and sulphides with which they are intergrown, provide a detailed record of the nature and evolution of parent body porosity and permeability, and the chemical composition, temperature and longevity of aqueous solutions. Fourteen meteorites were studied that range in petrologic subtype from mildly aqueously altered CM2.5 to completely hydrated CM2.0. All of them contain calcite, whereas aragonite occurs only in the CM2.5-CM2.2 meteorites and dolomite in the CM2.2-CM2.0. All of the aragonite crystals, and most of the calcite and dolomite grains, formed during early stages of parent body aqueous alteration by cementation of pores produced by the melting of tens of micrometre size particles of H2O-rich ice. Aragonite was the first carbonate to precipitate in the CM2.5 to CM2.2 meteorites, and grew from magnesium-rich solutions. In the least altered of these meteorites the aragonite crystals formed in clusters owing to physical restriction of aqueous fluids within the low permeability matrix. The strong correlation between the petrologic subtype of a meteorite, the abundance of its aragonite crystals and the proportion of them that have preserved crystal faces, is because aragonite was dissolved in the more altered meteorites on account of their higher permeability, and/or greater longevity of the aqueous solutions. Dolomite and breunnerite formed instead of aragonite in some of the CM2.1 and CM2.2 meteorites owing to higher parent body temperatures. The pore spaces that remained after precipitation of aragonite, dolomite and breunnerite cements were occluded by calcite. Following completion of cementation, the carbonates were partially replaced by phyllosilicates and sulphides. Calcite in the CM2.5-CM2.2 meteorites was replaced by Fe-rich serpentine and tochilinite, followed by Mg-rich serpentine. In the CM2.1 and CM2.0 meteorites dolomite, breunnerite and calcite were replaced by Fe-rich serpentine and Fe-Ni sulphide, again followed by Mg-rich serpentine. The difference between meteorites in the mineralogy of their replacive sulphides may again reflect greater temperatures in the parent body regions from where the more highly altered CMs were derived. This transition from Fe-rich to Mg-rich carbonate replacement products mirrors the chemical evolution of parent body solutions in response to consumption of Fe-rich primary minerals followed by the more resistant Mg-rich anhydrous silicates. Almost all of the CMs examined contain a second generation of calcite that formed after the sulphides and phyllosilicates and by replacement of remaining anhydrous silicates and dolomite (dedolomitization). The Ca and CO2 required for this replacive calcite is likely to have been sourced by dissolution of earlier formed carbonates, and ions may have been transported over metre-plus distances through high permeability conduits that were created by impact fracturing.

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

2014-11-01

216

Fluid mediated transformation of aragonitic cuttlebone to calcite  

NASA Astrophysics Data System (ADS)

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 ~370-390? 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 200? 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., Gmez-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., Gamsjger H., Knigsberger 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)

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

2009-04-01

217

Stabilit de l'association fayalite + calcite dans les formations ferrifres mtamorphoses ; l'exemple des minralisations en  

E-print Network

minerals of the ore bodies are magnetite, hematite, siderite, quartz, calcite, fayalite, hedenbergite and garnet, resulting from the metamorphism of siderite + calcite + quartz rocks with variable proportions

Boyer, Edmond

218

Stability of basalt+anhydrite+calcite at HP-HT: implications for Venus, the Earth and Mars  

NASA Astrophysics Data System (ADS)

Canali observed at Venus surface by Magellan are evidence for very long melt flows, but their composition and origin remain uncertain. The hypothesis of water-rich flow is not reasonable regarding Venus surface temperature. The length of these channels could not be explained by a silicate melt composition but more likely, by a carbonate-sulfate melt which has a much lower viscosity (Kargel et al 1994). One hypothesis is that 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 may release C- and S-rich melt or fluid. Another type of planetary phenomenon (affecting only the Earth) might provoke a high pressure destabilization of basalt+anhydrite+calcite. Very high contents of C and S are measured in some Earths 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 the subduction of an anhydrite-bearing oceanic crust, either directly (by melting followed by eruption) or indirectly (by release of S-rich melt or fluid that metasomatize the mantle). 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 1700C using a mixture of 70wt% tholeiitic basalt + 15wt% anhydrite + 15wt% calcite. Up to ~1440C, an ultracalcic (CaO>13.5 wt%; CaO/Al2O3>1 wt%) picrobasaltic (SiO2~40-45 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 ~1440C, 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 Earths 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.

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

2010-12-01

219

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

NASA Technical Reports Server (NTRS)

"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.

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

2010-01-01

220

Microbes Caught in the Act: Disentangling the Role of Biofilms in the Formation of Low Mg Calcite Ooids in a Freshwater Lake  

NASA Astrophysics Data System (ADS)

Biofilms and molds of cyanobacteria infilling depressions within the outermost cortex of ooids have been previously described in recent ooidal sands of Lake Geneva (Switzerland). Detailed sedimentological and mineralogical analyses of these ooids further indicated a low-Mg calcite composition of their cortex. Observed ooidal morphological features called for a fundamental role of biofilms triggering carbonate precipitation. A detailed microbiological study was much needed, however, in order to decipher the relative role of organic versus purely physicochemical processes during ooid formation. An experimental device consisting of frosted microscope slides was set at 2.50 m water depth in western Lake Geneva. These slides provide an attractive substrate for the microorganisms involved in low-Mg calcite precipitation allowing the in-situ harvesting of biofilms on a regular basis during more than three years. The inspection of the frosted slides showed the development of biofilms on their surface containing coccoid and filamentous cyanobacteria, heterotrophic bacteria and diatom frustules. Microscopical observations under natural light and autoflorescence show a close association between freshly low Mg-calcite precipitates and biofilms containing at least five species of filamentous and coccoid cyanobacteria. Carbonate precipitation peaks at early spring and late summer, and low Mg calcite crystals are always in close association with mostly cyanobacteria filaments (e.g., Tolipothrix, Oscillatoria). Ultra high-resolution elemental analyses performed immediately after recovering the samples confirmed the microscopical observations. Further SEM inspection of the samples revealed a clear seasonal pattern of carbonate precipitation identifying low Mg- calcite with crystal shapes varying from poorly to not crystallized compact aggregates; subautomorph to automorph rhomboedric crystals; and snowy cluster in which particles are very little or not crystallized. Liquid and solid cultures were further developed in the laboratory from the harvested biofilms allowing the determination of the microbial community using a PCR-DGGE approach. Two different primers were used to target all bacteria, and cyanobacteria and diatoms (341F-GC/907RM and 359F-GC/781 (a+b), respectively). Initial results indicate a similar microbial diversity between the sampled natural biofilms and those from BG11 enriched cultures. These data will allow us to design further laboratory experiments on low-Mg calcite precipitation including changes in pH, temperature and light intensity that mimic the natural biological and physicochemical cycle of the modern lake water throughout the year. Hence, this first dataset illustrates the significance of the in situ experiment to validate previous observations. Combined with the ongoing microbial cultures under laboratory-controlled conditions the outcome of our investigations will bring new light behind the role of biofilms in freshwater ooids formation.

Plee, K.; Ariztegui, D.; Sahan, E.; Martini, R.; Davaud, E.

2006-12-01

221

Arsenic-bearing calcite in natural travertines: evidence from sequential extraction, ?XAS, and ?XRF.  

PubMed

Recent studies demonstrated that synthetic calcite may host considerable amounts of arsenic (As). In this paper, the concentration of As in natural calcite was determined using two novel, specifically designed, sequential extraction procedures. In addition, the oxidation state of As and its distribution between calcite and coexisting Fe-oxyhydroxides was unravelled by ?XRF elemental mapping and As K-edge ?XAS spectroscopy. Our results conclusively demonstrate that arsenic can be found in natural calcite up to 2 orders of magnitude over the normal crustal As abundances. Because of the large diffusion of calcite in the environment, this phase may exert an important control on As geochemistry, mobility, and bioavailability. PMID:23738848

Costagliola, Pilario; Bardelli, Fabrizio; Benvenuti, Marco; Di Benedetto, Francesco; Lattanzi, Pierfranco; Romanelli, Maurizio; Paolieri, Mario; Rimondi, Valentina; Vaggelli, Gloria

2013-06-18

222

Fluoride removal in a fixed bed packed with granular calcite  

Microsoft Academic Search

A fixed bed reactor filled with calcite particles (mean strokes diameter, 0.20mm) was constructed and the reactor was used to treat synthetic wastewater containing HF, NaF, NH4F or Na2SiF6 under various conditions. Calcium ions (Ca2+) were found to exist in the treated effluent and the molar Ca2+ concentration ([Ca2+]) was related to the molar ratio of H+ to F? ([H+]0\\/[F?]0)

Min Yang; Takayuki Hashimoto; Nobuyuki Hoshi; Haruki Myoga

1999-01-01

223

Does Calcite Encrustation in Provide a Phosphorus Nutrient Sink?  

Microsoft Academic Search

We studied the effect of calcite encrustation in stoneworts (Chara spp.) on P cycling in an aquatic ecosystem. Sequential fractiona- tion was performed to quantify P fractions of the internodes of cal- cified (Ca-CF) and uncalcified (UCa-CF) Chara fibrosa Agardh ex Bruzelius. Our results showed that Ca-CF was able to store more P and about 14 to 23% of total

Kian Siong; Takashi Asaeda

2006-01-01

224

A re-evaluation of aragonite versus calcite seas  

Microsoft Academic Search

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

Mohammad H. Adabi

2004-01-01

225

Carbon isotopic thermometry calibrated by dolomite-calcite solvus temperatures  

NASA Astrophysics Data System (ADS)

The temperature dependence of carbon isotopic fractionations between calcite and graphite, and between dolomite and graphite are calibrated by the calcite-dolomite solvus geothermometry using marbles collected from the contact metamorphic aureole in the Kasuga area, central Japan. The carbon isotopic fractionations ( ?13CCc- Gr and ?13CDo? Gr) systematically decrease with increasing metamorphic temperature. The concordant relationships between the fractionations and solvus temperatures are approximately linear with T-2 over the temperature range. 400 to 680C: ?13CCc? Gr (%.) = 5.6 10 6 T-2 (K) - 2.4 ?13CDo? Gr (%.) = 5.9 10 6 T-2 ( K) - 1.9 These systematic relationships between fractionation and temperature suggest that carbon isotopic equilibria between carbonates and graphite were attained in many cases. The equation for the calcite-graphite system has a slope steeper than BOTTINGA'S (1969) results. It is, however, in good agreement with that of VALLEY and O'NEIL (1981) in the temperature range from 600 to 800C. Because of the relatively high sensitivity to temperature, these isotopic geothermometers are useful for determining the temperatures in moderate- to high-grade metamorphosed carbonate rocks.

Wada, Hideki; Suzuki, Kazuhiro

1983-04-01

226

Calcite deposition at Miravalles geothermal field, Costa Rica  

SciTech Connect

The calcite deposition problem at Miravalles has been studied since it was observed in the first three wells drilled on the slopes of the Miravalles Volcano. Long-term tests have been carried out to study reservoir characteristics. The change in the production behavior of the wells with the restriction imposed by the deposited calcite has been studied trying to evaluate and quantify the scaling problem. Work is being done on predictions of the deposition rate, location and distribution of the deposited mineral inside the wells. This work was compared with real data obtained from caliper logs of the wells before and after production. The feasibility of the first 55 MW power plant has been demonstrated. It was considered that the solution for the calcite problem is the reaming during discharge of the wells trying at the same time to minimize the cleaning interventions with a new well design. It is believed, due to the thermodynamics and chemical characteristics of the extracted fluids, that it is possible to find a non-deposition zone which will permit the drilling of wells without a scaling problem.

Vaca, L.; Alvarado, A.; Corrales, R. (Instituto Costarricense de Electricidad, San Jose (Costa Rica))

1989-01-01

227

Earthworm-produced calcite granules: A new terrestrial palaeothermometer?  

NASA Astrophysics Data System (ADS)

In this paper we show for the first time that calcite granules, produced by the earthworm Lumbricus terrestris, and commonly recorded at sites of archaeological interest, accurately reflect temperature and soil water ?18O values. Earthworms were cultivated in an orthogonal combination of two different (granule-free) soils moistened by three types of mineral water and kept at three temperatures (10, 16 and 20 C) for an acclimatisation period of three weeks followed by transfer to identical treatments and cultivation for a further four weeks. Earthworm-secreted calcite granules were collected from the second set of soils. ?18O values were determined on individual calcite granules (?18Oc) and the soil solution (?18Ow). The ?18Oc values reflect soil solution ?18Ow values and temperature, but are consistently enriched by 1.51 ( 0.12) in comparison to equilibrium in synthetic carbonates. The data fit the equation 1000 ln ? = [20.21 0.92] (103 T-1) - [38.58 3.18] (R2 = 0.95; n = 96; p < 0.0005). As the granules are abundant in modern soils, buried soils and archaeological contexts, and can be dated using U-Th disequilibria, the developed palaeotemperature relationship has enormous potential for application to Holocene and Pleistocene time intervals.

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

2013-12-01

228

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

PubMed

The crystal growth of calcite, the most stable calcium carbonate polymorph, in the presence of the cysteine-rich Mdm2 peptide (containing 48 amino acids in the ring finger configuration), has been investigated by the constant composition technique. Crystallization took place exclusively on well-characterized calcite crystals in solutions supersaturated only with respect to this calcium carbonate salt. The kinetic results indicated a surface diffusion spiral growth mechanism. The presence of the Mdm2 peptide inhibited the crystal growth of calcite by 22-58% in the concentration range tested, through adsorption onto the active growth sites of the calcite crystal surface. The kinetic results favored a Langmuir-type adsorption model, and the value of the calculated affinity constant was k(aff)=147x10(4) dm(3)mol(-1), a(ads)=0.29. PMID:16678843

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

2006-08-15

229

Bed-parallel calcite veins in the core of Wills Mountain anticline: Implications for deformation conditions and fluid flow during the Alleghanian orogeny  

Microsoft Academic Search

Thick, bed-parallel to sub-bed-parallel calcite veins are found in Upper Ordovician Trenton and Black River Group limestones exposed in the core of Wills Mountain anticline, Pendleton County, West Virginia. The veins range in thickness from less than 5 centimeters to over 2 meters, and contain individual crystals up to 20 centimeters across. The veins have a 1 to 3 mete

M. A. Evans; D. A. Battles

1994-01-01

230

Extension of self-seeding scheme with single crystal monochromator to lower energy < 5 keV as a way to generate multi-TW scale pulses at the European XFEL  

E-print Network

We propose a use of the self-seeding scheme with single crystal monochromator to produce high power, fully-coherent pulses for applications at a dedicated bio-imaging beamline at the European X-ray FEL in the photon energy range between 3.5 keV and 5 keV. We exploit the C(111) Bragg reflection (pi-polarization) in diamond crystals with a thickness of 0.1 mm, and we show that, by tapering the 40 cells of the SASE3 type undulator the FEL power can reach up to 2 TW in the entire photon energy range. The present design assumes the use of a nominal electron bunch with charge 0.1 nC at nominal electron beam energy 17.5 GeV. The main application of the scheme proposed in this work is for single shot imaging of individual protein molecules.

Geloni, Gianluca; Saldin, Evgeni

2012-01-01

231

Strontium isotope fractionation of planktic foraminifera and inorganic calcite  

NASA Astrophysics Data System (ADS)

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

Bhm, Florian; Eisenhauer, Anton; Tang, Jianwu; Dietzel, Martin; Krabbenhft, Andre; Kisakrek, Basak; Horn, Christian

2012-09-01

232

Seed Size  

NSDL National Science Digital Library

In this activity, learners collect, arrange, and draw various seeds from smallest to biggest. They also estimate how many of the smallest would fit into the biggest. In addition, learners predict how many seeds they would find inside an apple or lemon, and cut open these fruits to check their prediction against the real seed count. The Did You Know section describes the biggest and smallest seeds on Earth.

Science, Lawrence H.

2007-01-01

233

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

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

234

Top-Seeded Solution Growth of Pb[(In1/2Nb1/2),(Mg1/3Nb2/3),Ti]O3 Single Crystals  

NASA Astrophysics Data System (ADS)

The crystal growth of relaxor-based ferroelectric single crystals Pb[(In1/2Nb1/2),(Mg1/3Nb2/3),Ti]O3 (PIMNT) was investigated using the top-seeded solution growth (TSSG) method. The concentration of Pb(In1/2Nb1/2)O3 in a melt was chosen to be 0.24 mole, and that of Pb(Mg1/3Nb2/3)O3 was changed from 0.36 to 0.42 mole. A mixture of PbO+B2O3 was used as a flax and the melt composition was PIMNT/PbO/B2O3=70/29/1 wt%. The obtained crystals showed that the concentration of Pb(In1/2Nb1/2)O3 slightly changed but that of Pb(Mg1/3Nb2/3)O3 increased by about 12%, 0.05 mole, compared to those of the melt. All crystals had a complete perovskite structure. A crystal with a composition of Pb[(In1/2Nb1/2)0.24(Mg1/3Nb2/3)0.43Ti0.33]O3 was obtained, and its Curie temperature was Tc = 208C and rhombohedral-to-tetragonal phase transition temperature was Trt = 120C. A phase diagram for crystal growth near the morphotropic phase boundary mentioned above was obtained.

Karaki, Tomoaki; Nakamoto, Maki; Sumiyoshi, Yoichi; Adachi, Masatoshi; Hosono, Yasuharu; Yamashita, Yohachi

2003-09-01

235

In situ study on ?11B and B/Ca in synthetic aragonite and calcite: the effect of growth rate and temperature  

NASA Astrophysics Data System (ADS)

Boron isotopic and chemical content of carbonates (expressed as ?11B and B) is being developed as seawater pH and CO32- proxy. However, thermodynamic and kinetic effects on ?11B and B are not well understood. It underscores the importance of exploring possible effects of temperature and growth rate on ?11B and B fractionation in synthetic calcium carbonate minerals, which is the focus of this study. In situ Secondary Ion Mass Spectrometry (SIMS) analyses of ?11B were conducted in the aragonite spherulites precipitated from seawater at 50C, 65C and 75C. Here spherulite centers represent the onset of crystallization with the rates that are significantly higher than those of the later grown fibres [1,2]. Boron isotopic composition reflects these two morphologically distinct domains: ?11B (centers) are lower than ?11B (fibres) by up to one order of magnitude. This observation is consistent with ?11B difference between coral early mineralization zone and fibrous aragonite [3]. Also, our preliminary results suggest averaged ?11B (centers+fibres) increases with temperature within the range of 55 to 75C. SIMS measurements of B/Ca were performed on single crystals of calcites synthesized from laboratory prepared solution of NH4Cl-CaCl2 doped with boron by diffusion of CO2. Growth rates of calcite (V) within crystals grown isothermally (T=2, 15, 20, 22 and 25C) were monitored by sequentially spiking calcite-precipitating fluids with rare earth element (REE) dopants. The REE were analyzed with SIMS at spots matching those where B/Ca were determined. REE patterns reveal concentric domains of calcite growth. The growth rate of calcite generally decreases with time - i.e., crystal rims advanced at slower rates than cores. Fluids were sampled periodically for B, Ca, dissolved inorganic carbon, and pH. Boron Nernst partition coefficient DB=B(calcite)/B(fluid) increases from 0.38 (pH=8.110.04) to 0.68 (pH=8.030.03) with increasing V from 0.039 to 0.12 nm/s at 25C. Also, DB potentially decreases with increasing of temperature at the range of 20 to 25C. We anticipate presenting DB for the full studied temperature range. The depletion of 11B in the centers of aragonite spherulite relative to its fibres suggests the reverse relationship of ?11B with aragonite growth rate. Our results in synthetic calcite suggest both temperature and especially growth rate should be accounted while using boron as pH or CO32- recorder in biogenic calcite. pH effect was masked by V while pH increased from 8 to 8.15 during calcite precipitation at 25C. [1] Gabitov et al. (2008) Geochim. Cosmochim. Acta, 73, 4166-4179. [2] Holcomb et al. (2009) Geochim. Cosmochim. Acta, 72, 4058-4068. [3] Blamart et al. (2007) G-cubed, Q12001, doi:10.1029/2007GC001686.

Gabitov, R. I.; Rollion-Bard, C.; Sadekov, A.

2011-12-01

236

Phosphoprotein modulation of apatite crystallization  

Microsoft Academic Search

SummarySeveral 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

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

1980-01-01

237

The sensitized luminescence of manganese-activated calcite  

USGS Publications Warehouse

Synthetic manganese-activated calcites are shown to be practically inert to ultraviolet excitation in the range 2000-3500A, while they are luminescent under cathode-ray excitation. The incorporation of small amounts of an auxiliary impurity along with the manganese produces the strong response to ultraviolet radiation hitherto ascribed to CaCO3:Mn itself. Three such impurities have been studied: lead, thallium, and cerium. The first two induce excitation in the neighborhood of the mercury resonance line, while the cerium introduces a response principally to longer wave ultraviolet. The strong response to 2537A excitation shown by some natural calcites is likewise found to be due to the presence of lead along with the manganese, rather than to the manganese alone. The data do not warrant ascribing the longer wave-length ultraviolet-excited luminescence of all natural calcites to the action of an auxiliary impurity. The essential identity of the cathode-ray excited luminescence spectra of CaCO 3:Mn, CaCO3: (Pb+Mn), CaCO3:(Tl+Mn), and CaCO3:(Ce+Mn) with the 2537A-excited spectra of the latter three is evidence that the luminescent center in all cases is the manganese ion or the MnO6 group. It is shown that a "cascade" mechanism for the action of the auxiliary impurities, lead, thallium, and cerium, is incorrect; and that the phenomenon must be considered as a case of sensitized luminescence. Owing to the nature of cathode-ray excitation, the manganese activator can be excited by this agent even in the absence of a second impurity. For optical excitation, however, an absorption band for the ultraviolet must be established by building into the CaCO3:Mn a second impurity or "sensitizer.".

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

1947-01-01

238

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

NASA Astrophysics Data System (ADS)

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.

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

2004-07-01

239

Patterns of biomediated CaCO3 crystal bushes in hot spring deposits  

NASA Astrophysics Data System (ADS)

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

Peng, Xiaotong; Jones, Brian

2013-08-01

240

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

Microsoft Academic Search

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 900C at a rate of 300C\\/h, with a quadrupole mass spectrometer. Crushed calcite released water in

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

2008-01-01

241

Geochemistry of post-uplift calcite in the Permian Basin of Texas and New Mexico  

Microsoft Academic Search

Integration whole-oil gas chromatography of produced oil and oil inclusions, formation-water chemistry, and stable isotopes has identified environment-diagnostic differences in calcite cements between oil field and outcrop environments in the Permian Basin of Texas and New Mexico. Calcite-[delta][sup 13]C and fluid-inclusion composition are the most diagnostic of pore-fluid evolution and can help interpret rock-fluid reactions. Late-stage calcite cement in the

W. D. Wiggins; P. M. Harris; R. C. Burruss

1993-01-01

242

Influence of Calcite and Dissolved Calcium on Uranium(VI) Sorption to a Hanford Subsurface Sediment  

Microsoft Academic Search

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

Wenming Dong; William P. Ball; Chongxuan Liu; Zheming Wang; Alan T. Stone; Jing Bai; John M. Zachara

2005-01-01

243

Hydrodynamic control of inorganic calcite precipitation in Huanglong Ravine, China: Field measurements and theoretical prediction of deposition rates  

NASA Astrophysics Data System (ADS)

Hydrochemical and hydrodynamical investigations are presented to explain tufa deposition rates along the flow path of the Huanglong Ravine, located in northwestern Sichuan province, China, on an altitude of about 3400 m asl. Due to outgassing of CO 2 the mainly spring-fed stream exhibits, along a valley of 3.5 km, calcite precipitation rates up to a few mm/year. We have carried out in situ experiments to measure calcite deposition rates at rimstone dams, inside of pools and in the stream-bed. Simultaneously, the downstream evolution of water chemistry was investigated at nine locations with respect to Ca 2+, Mg 2+, Na +, Cl -, SO 42-, and alkalinity. Temperature, pH, and conductivity were measured in situ, while total hardness, Ca T, and alkalinity have been determined immediately after sampling, performing standard titration methods. The water turned out to be of an almost pure Ca?Mg?HCO 3 type. The degassing of CO 2 causes high supersaturation with respect to calcite and due to calcite precipitation the Ca 2+ concentration decreases from 610 -3 mole/1 upstream down to 2.510 -3 mole/1 at the lower course. Small rectangular shaped tablets of pure marble were mounted under different flow regimes, i.e., at the dam sites with fast water flow as well as inside pools with still water. After the substrate samples had stayed in the water for a period of a few days, the deposition rates were measured by weight increase, up to several tens of milligrams. Although there were no differences in hydrochemistry, deposition rates in fast flowing water were higher by as much as a factor of four compared to still water, indicating a strong influence of hydrodynamics. While upstream rates amounted up to 5 mm/year, lower rates of about 1 mm/year were observed downstream. Inspection of the marble substrate surfaces by EDAX and SEM (scanning electron microscope) revealed authigeneously grown calcite crystals of about 10 ?m. Their shape and habit are indicative of a chemically controlled inorganic origin. By applying a mass transfer model for calcite precipitation taking into account the reaction rates at the surface given by Plummer et al. (1978), slow conversion of CO 2 into H + and HCO 3- , and diffusional mass transport across a diffusion boundary layer, we have calculated the deposition rates from the hydrochemistry of the corresponding locations. The calculated rates agree within a factor of two with the experimental results. Our findings confirm former conclusions with respect to fast flow conditions: reasonable rates of calcite precipitation can be estimated in reducing the PWP-rate calculated from the chemical composition of the water by a factor of about ten, thus correcting for the influence of the diffusion boundary layer.

Zaihua, Liu; Svensson, U.; Dreybrodt, W.; Daoxian, Yuan; Buhmann, D.

1995-08-01

244

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

PubMed

In this study, porous calcite materials are hydrothermally treated at 200C using powder compacts consisting of calcite and glasses composed of silica-rich soda-lime. After treatment, the glasses are converted into calcium aluminosilicate hydrates, such as zeolite phases, which increase their strength. The porosity and morphology of new deposits of hydrothermally solidified materials depend up on the chemical composition of glass. The use of calcite and glass in the hydrothermal treatment plays an important role in the solidification of calcite without thermal decomposition. PMID:21794973

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

2011-11-01

245

Environmental controls on the Emiliania huxleyi calcite mass  

NASA Astrophysics Data System (ADS)

Although ocean acidification is expected to impact (bio) calcification by decreasing the seawater carbonate ion concentration, [CO32-], there is evidence of nonuniform response of marine calcifying plankton to low seawater [CO32-]. This raises questions about the role of environmental factors other than acidification and about the complex physiological responses behind calcification. Here we investigate the synergistic effect of multiple environmental parameters, including seawater temperature, nutrient (nitrate and phosphate) availability, and carbonate chemistry on the coccolith calcite mass of the cosmopolitan coccolithophore Emiliania huxleyi, the most abundant species in the world ocean. We use a suite of surface (late Holocene) sediment samples from the South Atlantic and southwestern Indian Ocean taken from depths lying above the modern lysocline (with the exception of eight samples that are located at or below the lysocline). The coccolith calcite mass in our results presents a latitudinal distribution pattern that mimics the main oceanographic features, thereby pointing to the potential importance of seawater nutrient availability (phosphate and nitrate) and carbonate chemistry (pH and pCO2) in determining coccolith mass by affecting primary calcification and/or the geographic distribution of E. huxleyi morphotypes. Our study highlights the importance of evaluating the combined effect of several environmental stressors on calcifying organisms to project their physiological response(s) in a high-CO2 world and improve interpretation of paleorecords.

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

2014-04-01

246

Porosity and hydric behavior of typical calcite microfabrics in stalagmites  

NASA Astrophysics Data System (ADS)

Petrophysical techniques commonly used for material characterization are applied for the first time to speleothem samples to investigate the porosity and hydric behavior of calcite stalagmites used in paleoclimatology. These techniques allow the determination of the stalagmites' potential to undergo diagenetic transformations when substantial changes in drip waters occur in the cave environment. The petrophysical techniques include water absorption under vacuum and by capillarity, nuclear magnetic resonance, environmental scanning electron microscopy, and mercury intrusion porosimetry. The studied samples comprise five common calcite microfabrics, which have markedly different porosities and hydric behaviors and, as a consequence, different sensibilities to diagenetic processes related to the influx of water. The experiments show that stalagmites can behave as complex, small-scale hydrological systems and that the circulation of water through them by complex nets of interconnected pores might be common. As the circulation of water favors diagenetic transformations that involve geochemical and isotopic changes, the characterization of flow patterns is key for outlining areas that are susceptible to such modifications, which is critical to paleoclimatic studies that are based on speleothems because geochemical and stable isotopic data are used as paleoenvironmental proxies and absolute ages are obtained by using radioactive isotope ratios. These potential modifications also have obvious implications for studies based on fluid inclusions in speleothems. The integrated methodology, which uses primarily non-destructive techniques, shows a high potential for characterization of any type of speleothem and other continental carbonates such as tufas or sinters.

Muoz-Garca, M. B.; Lpez-Arce, P.; Fernndez-Valle, M. E.; Martn-Chivelet, J.; Fort, R.

2012-07-01

247

Brine induced low-Magnesium calcite formation at cold seeps  

NASA Astrophysics Data System (ADS)

Low-Mg calcite (LMC; < 5 mol% Mg), commonly observed during time intervals of "calcite seas," since the beginning of the Paleozoic Era, is a good indicator of low Mg/Ca ratio (< 2) in seawater. Calcite seas were coincident with times of active seawater-basalt interactions along mid-ocean ridges at high temperatures, which extract Mg from seawater and release Ca to it. In the modern aragonite sea, most carbonate minerals precipitate at the seafloor, including deposits from cold seep environments are primarily either aragonite or high-Mg calcite (HMC). Here, we report the finding of non-skeletal LMC from cold seeps in Alaminos Canyon block 601 (AC 601), 2200 m below the sea surface on northern Gulf of Mexico (GOM) continental slope. Low-Mg calcite usually represents the only carbonate mineral in the studied samples. Dominant allochems in these seep carbonates are peloids, grain aggregates, pelagic forams, and fragments of mollusks and echinoids. The limestone is heavily cemented. The observed cements include micrite, microspar, mosaic, bladed, fan, and needle cements. The dissolution of grains and cements was observed. Not only originally aragonitic mollusks shells, but also carbonate cement have been dissolved. The aerobic oxidation of reduced chemical species such as methane and H2S is responsible for an increase in pCO2 and a decrease of pH, leading to local carbonate dissolution. The occurrence of oxic conditions is confirmed by the presence of negative Ce anomalies of the carbonates. Further, we report on analyses showing that the ambient porewater Mg/Ca ratio actually governs the carbonate mineralogy. The occurrence of LMC may be attributed to the brine fluids, which is relatively Mg-depleted (Mg/Ca mole ratio is below 0.7) compared to pore fluid of the subsurface sediments from the reference site (Mg/Ca mole ratio is above 4.1) that usually produce HMC. The 87Sr/86Sr values of LMC (mean = 0.708001, sd = 0.000034, n=2) are significantly lower than that of the seawater (0.709175). Strong deviation of the Sr isotope ratios of LMC from seawater is interpreted as the modification of the strontium from less radiogenic sources like older marine sediments and/or the locally abundant Jurassic salt. Therefore, we speculate that the seep fluids at the studied site most likely have a deep origin and may also have been influenced by dissolved halite during their ascent through conduits along the margins of salt bodies. The understanding of the processes that control the LMC precipitation in the GOM will also contribute to an improved understanding of the presence or absence of LMC in other oceans margin settings today, and in geological deposits as well.

Feng, Dong; Roberts, Harry; Joye, Samantha; Heydari, Ezat

2013-04-01

248

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

PubMed

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

Wang, Tongxin; Clfen, Helmut; Antonietti, Markus

2005-03-16

249

A novel insulin microcrystals preparation using a seed zone method  

NASA Astrophysics Data System (ADS)

Milling and supercritical fluid technology have been used to prepare particles suitable for pulmonary delivery, but problems remain, e.g., the loss of protein activity, the heterogeneity of drug particles including shape, size etc., process yield, and the applicability for industrial production process. Therefore, in order to develop a novel process for particle preparation, crystallization was investigated using insulin as a model protein. The relation between the number of seed particles and the final crystal size was investigated, and a novel microcrystallization process, named seed zone method, was developed. The size of crystals was inversely proportional to the number of seeds in crystallizing solution. Spontaneous crystallization occurred around pH 6 in acetic acid solution, however, more than 60% of crystals were bigger than 5 ?m with two peak size distributions. On the contrary, microcrystals with a mean diameter of 3 ?m were prepared using a seed zone method. The seed zone is a pH range where the seed particles are stable in crystallizing solution. Almost 90% (in volume) of microcrystals were under 5 ?m, and the yield of crystallization was maintained at 90% or higher. In the seed zone, nano-sized particles (96 nm) with narrow size distributions were identified. Therefore, it is likely that these nano-sized particles would be used as seeds in microcrystals formation. It is suggested that insulin microcrystallization using a seed zone could be a useful particle preparation process in pharmaceutical industry.

Kwon, Jai-Hyun; Kim, Chan-Wha

2004-03-01

250

Seeding of high temperature air flow  

Microsoft Academic Search

Seeding of high temperature air flows is problematic because common seeding materials can ignite and may pose a threat for\\u000a human health in case of inhalation. Sodium chloride is proposed as a seeding material to avoid these problems. The generation\\u000a of crystals using an ultrasonic atomizer is described and the measured particle size distribution is presented. The described\\u000a method has

D. Rusch; A. Kempe; T. Roesgen

2007-01-01

251

Statistical Evaluation of Cloud Seeding Operations  

Microsoft Academic Search

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

K. A. Brownlee

1960-01-01

252

Scattering Seeds  

NSDL National Science Digital Library

In this lesson, students will: 1) Investigate how seeds are dispersed. 2) Understand the variety of seed dispersal that exists in the plant kingdom. 3) Understand how factors in the natural environment can effect how far a seed is dispersed. Included in this one to two day lesson plan are the objectives, needed materials, procedures, adaptations for older students, discussion questions, an evaluation, extensions, suggested reading, links to other sites, vocabulary, and academic standards. Students will collect a variety of seeds and design a wind-dispersed seed mechanism. They can click on a vocabulary word to hear its pronunciation and a sentence using the word. Teachers can purchase the video, The Private Life of Plants 5-Pack (Branching Out) and download comprehension questions and answers. They can link to Teaching Tools to create custom worksheets, puzzles, and quizzes. A printable version of this lesson plan can be downloaded.

Discoveryschool.com; Cahill, Mary

2007-01-01

253

Reconciling disparate views of template-directed nucleation through measurement of calcite nucleation kinetics and binding energies  

PubMed Central

The physical basis for how macromolecules regulate the onset of mineral formation in calcifying tissues is not well established. A popular conceptual model assumes the organic matrix provides a stereochemical match during cooperative organization of solute ions. In contrast, another uses simple binding assays to identify good promoters of nucleation. Here, we reconcile these two views and provide a mechanistic explanation for template-directed nucleation by correlating heterogeneous nucleation barriers with crystalsubstrate-binding free energies. We first measure the kinetics of calcite nucleation onto model substrates that present different functional group chemistries (carboxyl, thiol, phosphate, and hydroxyl) and conformations (C11 and C16 chain lengths). We find rates are substrate-specific and obey predictions of classical nucleation theory at supersaturations that extend above the solubility of amorphous calcium carbonate. Analysis of the kinetic data shows the thermodynamic barrier to nucleation is reduced by minimizing the interfacial free energy of the system, ?. We then use dynamic force spectroscopy to independently measure calcitesubstrate-binding free energies, ?Gb. Moreover, we show that within the classical theory of nucleation, ? and ?Gb should be linearly related. The results bear out this prediction and demonstrate that low-energy barriers to nucleation correlate with strong crystalsubstrate binding. This relationship is general to all functional group chemistries and conformations. These findings provide a physical model that reconciles the long-standing concept of templated nucleation through stereochemical matching with the conventional wisdom that good binders are good nucleators. The alternative perspectives become internally consistent when viewed through the lens of crystalsubstrate binding. PMID:24434555

Hamm, Laura M.; Giuffre, Anthony J.; Han, Nizhou; Tao, Jinhui; Wang, Debin; De Yoreo, James J.; Dove, Patricia M.

2014-01-01

254

Origin of cone-in-cone calcite veins during calcitization of dolomites and their subsequent diagenesis: A case study from the Gogolin Formation (Middle Triassic), SW Poland  

Microsoft Academic Search

Although bedding-parallel cone-in-cone structure calcite veins are present in the Middle Triassic Gogolin Formation in Opole Silesia, their occurrence is limited to the Emilwka Cellular Limestone Member. Marly limestones (dedolomites) consisting of calcite pseudospar are the host rocks. The veins, which are up to 3mm high and 30cm long, are built of densely packed cone columns, with individual cones up

Monika Kowal-Linka

2010-01-01

255

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

[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.

Bjoerkum, P.A. (Statoil, Stavanger (Norway)); Walderhaug, O. (Rogaland Research, Stavanger (Norway))

1993-07-01

256

Age constraints on fluid inclusions in calcite at Yucca Mountain  

SciTech Connect

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

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

2001-04-29

257

Calcite orientations and composition ranges within teeth across Echinoidea.  

PubMed

Sea urchin's teeth from four families of order Echinoida and from orders Temnopleuroida, Arbacioida and Cidaroida were studied with synchrotron X-ray diffraction. The high and very high Mg calcite phases of the teeth, i.e. the first and second stage mineral constituents, respectively, have the same crystallographic orientations. The co-orientation of first and second stage mineral, which the authors attribute to epitaxy, extends across the phylogenic width of the extant regular sea urchins and demonstrates that this is a primitive character of this group. The range of compositions ?x for the two phases of Ca1-xMgxCO3 is about 0.20 or greater and is consistent with a common biomineralization process. PMID:25158180

Stock, Stuart R; Ignatiev, Konstantin; Lee, Peter L; Almer, Jonathan D

2014-08-01

258

Improved strength and durability of fly ash-amended concrete by microbial calcite precipitation  

Microsoft Academic Search

Fly ash acts as a partial replacement material for both Portland cement and fine aggregate. An innovative approach of microbial calcite precipitation in fly ash-amended concrete has been investigated. This is the first report to discuss the role of microbial calcite precipitation in enhancing the durability of fly ash-amended concrete. The present study investigated the effects of Bacillus megaterium ATCC

Varenyam Achal; Xiangliang Pan; Nilfer zyurt

2011-01-01

259

In-situ synchrotron X-ray reflectivity measurements at the calcite-water interface  

NASA Astrophysics Data System (ADS)

In-situ synchrotron X-ray reflectivity (SXR) measurements of the calcite-water interface were made. These data were used to model the angstrom-scale interfacial width and electron density profile of the interface. Measurements were made on the (10T4) cleavage surface of Iceland spar calcite in contact with pure N 2, humid N 2, deionized water, and dilute nitric acid solutions at 25C. The measurements were performed in an X-ray transparent reaction cell in which fluid pH was monitored during SXR data acquisition. Analysis of the data indicated that the pristine calcite surface in contact with pure N 2 has an interfacial width (statistical roughness) of 2.60 0.15 . Exposure to water vapor (humid N 2) resulted in the deposition of a water film 19.9 0.4 thick. There was no evidence from the SXR data that the adsorbed water film caused roughening of the calcite surface. However, when reacted with deionized water the calcite was roughened, yielding an interfacial width of 23.1 . During successive reactions with fluids having decreasing initial pH the calcite/fluid interfacial width increased from 23.1 to 45.3 . The SXR results indicate that intraterrace areas participate in the dissolution of calcite. A linear correlation was observed between interfacial width of the intraterrace areas and the quantity of calcite dissolved.

Chiarello, Ronald P.; Wogelius, Roy A.; Sturchio, Neil C.

1993-08-01

260

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

Microsoft Academic Search

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,

Art F White; T HOMAS D. BULLEN; DAVISON V. VIVIT; MARJORIE S. SCHULZ; DAVID W. CLOW

1999-01-01

261

Uranium in foraminiferal calcite as a recorder of seawater uranium concentrations  

Microsoft Academic Search

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

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

1994-01-01

262

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

Microsoft Academic Search

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

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

2009-01-01

263

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

E-print Network

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

Asmerom, Yemane

264

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

NASA Astrophysics Data System (ADS)

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.

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

2003-12-01

265

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

USGS Publications Warehouse

The CO2 combined as calcite in carbonate-bearing apatites as been distinguished from that combined as carbonate-apatite, or present in some form other than calcite, by use of X-ray powder patterns, differential thermal analyses, and differential solubility tests. These methods were applied to several pure apatite minerals, to one fossil bone, and to a group of phosphorites from the Phosphoria formation of Permian age from Trail Canyon and the Conda mine, Idaho, and the Laketown district, Utah. With the exceptions of pure fluorapatite, pure carbonate-flueorapatite, and one phosphorite from Trail Canyon, these substances contain varying amounts of calcite, but in all the samples an appreciable part of the carbonite content is not present as calcite. The results of solubility tests, in which the particle size of sample and the length of solution time were varied, imply that the carbonate content is not due to shielded calcite entrapped along an internal network of surfaces.

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

1951-01-01

266

Microbially Induced Calcite Precipitation-based Sequestration of Strontium by Sporosarcina pasteurii WJ-2.  

PubMed

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

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

2014-12-01

267

Cd 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)  

NASA Astrophysics Data System (ADS)

Cadmium uptake by calcite from aqueous solution was studied using techniques sensitive to the near-surface: X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). These techniques allowed direct observations of structure and bonding environments at the calcite surface. The results indicate that the main processes involved in cadmium uptake by calcite are adsorption and solid-state diffusion into the crystal, which leads eventually to the formation of solid-solution. Pure calcite crystals were cleaved from precleaned Iceland spar and were briefly exposed to aqueous solutions containing various concentrations of Cd 2+, CO 32-, ClO 4-, and/or Cl -. Some Cd 2+ was radiolabelled. LEED results demonstrate that the calcite surface is atomically ordered, even after hydration and cadmium uptake. ?-scintillation data from crystals exposed briefly to solutions of 109Cd 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 , but crystals stored in air or in ultra-high vacuum showed a decrease in Cd surface concentration with time such that after two days, Cd was barely detectable in the near-surface region. In other experiments, LEED verified the crystallinity of otavite (CdCO 3) grown epitaxially over the {101} cleavage faces of calcite, and XPS showed almost no Ca in the near-surface on scans taken immediately after precipitation; but after storage for a month in ultrahigh vacuum, binding energy shifts and the presence of a Ca peak strongly suggested the development of solid-solution by diffusion through the solid. 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.

Stipp, Susan L.; Hochella, Michael F., Jr.; Parks, George A.; Leckie, James O.

1992-05-01

268

Diel cycles in calcite production and dissolution in a eutrophic basin  

SciTech Connect

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.

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

1999-10-01

269

Titania single crystals with a curved surface.  

PubMed

Owing to its scientific and technological importance, crystallization as a ubiquitous phenomenon has been widely studied over centuries. Well-developed single crystals are generally enclosed by regular flat facets spontaneously to form polyhedral morphologies because of the well-known self-confinement principle for crystal growth. However, in nature, complex single crystalline calcitic skeleton of biological organisms generally has a curved external surface formed by specific interactions between organic moieties and biocompatible minerals. Here we show a new class of crystal surface of TiO2, which is enclosed by quasi continuous high-index microfacets and thus has a unique truncated biconic morphology. Such single crystals may open a new direction for crystal growth study since, in principle, crystal growth rates of all facets between two normal {101} and {011} crystal surfaces are almost identical. In other words, the facet with continuous Miller index can exist because of the continuous curvature on the crystal surface. PMID:25373513

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

2014-01-01

270

Kinetics of Mg partition and Mg stable isotope fractionation during its incorporation in calcite  

NASA Astrophysics Data System (ADS)

Calcite growth experiments have been performed in the presence of aqueous Mg at 25 C and 1 bar pCO2 to quantify magnesium partition coefficient D={(Mg/Ca)}/{(Mg/Ca)} and Mg isotope fractionation between calcite and reactive fluid (?26Mgcalcite-fluid) as a function of calcite precipitation rate rp (mol m-2 s-1). Mg partition coefficient, DMg, increases with calcite growth rate according to: LogD=0.2517(0.0150)Logrp+0.0944(0.0182); R2=0.93,(10-8.3?rp?10-6.6molms) ?26Mgcalcite-fluid was found to depend heavily on calcite growth rate with preferential incorporation of 24Mg in calcite and the extent of isotope fractionation decreasing with increasing calcite growth rate in accord with: ?26Mg=0.7918(0.0452)Logrp+3.2366(0.3360); R2=0.97(10-8.3?rp?10-6.6molms) The negative ?26Mgcalcite-fluid values found in this study, with calcite overgrowths enriched in light Mg, are consistent with (i) recent experimental data on Mg isotope fractionation during low-Mg calcite homogeneous precipitation (Immenhauser et al., 2010) and magnesite growth (Pearce et al., 2012) and (ii) with theoretical values calculated for Mg-calcite by density-functional electronic structure models (Rustad et al., 2010). The deviation of the isotopic composition of precipitated Mg-calcite from the equilibrium mass fractionation line in a three isotope diagram is a linear function of calcite growth rate. The equilibrium ?26Mgcalcite-fluid value at 25 C derived from this linear extrapolation, ?26Mgcalcite-fluid = -3.5 0.2 (2?), is in good agreement with the theoretical value calculated by Rustad et al. (2010) for Mg-calcite (?26Mgcalcite-fluid = -3.6; BP86 functional). A striking feature of the results of this study is the decrease of the extent of Mg isotope fractionation (from -3.16 to -1.88) with the increase of calcite precipitation rate (from 10-8.3 to 10-6.6 mol m-2 s-1) which is opposite to the variation of Ca, Ba and Sr isotope fractionation with calcite precipitation rate. This behavior likely stems from the strong free energy of hydration of the Mg2+ ion compared to Ca2+, Ba2+ and Sr2+ which leads, during fast calcite growth, to the entrapment in calcite overgrowths of hydrated Mg ions whose isotopic composition is close to that of aqueous Mg2+. The strong dependence of Mg isotope fractionation on calcite growth rate suggests that, using the three isotopes method, Mg isotopic signatures of calcite in association with those of other divalent metals (Zn2+, Cu2+) have the potential to reveal mineral precipitation rates and thus environmental conditions of the oceans over geological time.

Mavromatis, Vasileios; Gautier, Quentin; Bosc, Olivier; Schott, Jacques

2013-08-01

271

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

NASA Astrophysics Data System (ADS)

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

Hong, Mina; Teng, H. Henry

2014-09-01

272

Seeding Rangeland  

E-print Network

easily. Following a wildfire, seeding may be necessary to restore the area?s productivity. On abandoned cropland, an ideal seedbed may be prepared without undue expense, but on rangeland, the ideal seedbed is a goal seldom attained because expenses exceed... easily. Following a wildfire, seeding may be necessary to restore the area?s productivity. On abandoned cropland, an ideal seedbed may be prepared without undue expense, but on rangeland, the ideal seedbed is a goal seldom attained because expenses exceed...

Welch, Tommy G.; Hafercamp, Marshall R.

2001-01-04

273

String stabilized ribbon growth a method for seeding same  

DOEpatents

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.

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

1987-08-25

274

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

NASA Astrophysics Data System (ADS)

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.

Milliere, Laure; Verrecchia, Eric; Gussone, Nikolaus

2014-05-01

275

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

PubMed

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

Bernth, Balzs; Blah, Mikls; Egri, Adm; Barta, Andrs; Kriska, Gyrgy; Horvth, Gbor

2013-09-01

276

Stability of the association fayalite + calcite within metamorphosed banded iron formations: the case of the magnetite ores of Edough massif (N-E  

E-print Network

. The main minerals of the ore bodies are magnetite, hematite, siderite, quartz, calcite, fayalite, hedenbergite and garnet, resulting from the metamorphism of siderite + calcite + quartz rocks containing

Paris-Sud XI, Université de

277

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

278

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.

279

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.

280

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

E-print Network

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

Cirpka, Olaf Arie

281

Simulation of calcite dissolution and porosity changes in saltwater mixing zones in coastal aquifers  

USGS Publications Warehouse

Thermodynamic models of aqueous solutions have indicated that the mixing of seawater and calcite-saturated fresh groundwater can produce a water that is undersaturated with respect to calcite. Mixing of such waters in coastal carbonate aquifers could lead to significant amounts of limestone dissolution. The potential for such dissolution in coastal saltwater mixing zones is analyzed by coupling the results from a reaction simulation model (PHREEQE) with a variable density groundwater flow and solute transport model. Idealized cross sections of coastal carbonate aquifers are simulated to estimate the potential for calcite dissolution under a variety of hydrologic and geochemical conditions. Results show that limestone dissolution in mixing zones is strongly dependent on groundwater flux and nearly independent of the dissolution kinetics of calcite. -from Authors

Sanford, W. E.; Konikow, L. F.

1989-01-01

282

High School Forum: "Invitations to Enquiry": The Calcite/Acid Reaction.  

ERIC Educational Resources Information Center

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)

Herron, J. Dudley, Ed.; Driscoll, D. R.

1979-01-01

283

Non-Markovian behavior of ultrafast coherent ionization dynamics in a crystal exposed to a seeded free-electron-laser pulse  

NASA Astrophysics Data System (ADS)

We investigate the ionization dynamics of a crystal structure driven by ultrafast coherent x-ray pulses of moderate to high intensities for excitations where dipole-allowed, single-photon ionization dominates. Using a simple model of the crystal, we demonstrate that quantum coherences may already play an important role at moderate pulse intensities, leading to qualitatively novel features which cannot be described by rate equations. In particular, the ionization may exhibit a minimum as a function of the pulse duration, where the ionization drops to almost zero, although during the pulse a noticeable fraction of the electrons is promoted to unbound states. For higher intensities, the qualitative deviations between the coherent quantum-mechanical treatment and the rate description is even more pronounced. In particular, due to the presence of quantum-mechanical coherences, the full theory predicts, even for the single-photon transitions to a continuum of free-electron states, a Rabi-type behavior similar to what is known for two-level systems.

Brand, A.; Kaiser, B.; Vagov, A.; Axt, V. M.; Pietsch, U.

2014-06-01

284

Distribution of vesicular-arbuscular mycorrhizal fungi in coal, lignite, and calcite mine spoils of India  

Microsoft Academic Search

We assessed vesicular-arbuscular mycorrhizal (VAM) fungi in coal, lignite, and calcite mine spoils. The level of VAM fungal infection and the population of VAM species in plants on the coal-waste sites were similar to those in plants on the calcite mine spoil. The plants on the coal-waste sites and their associated VAM fungi included Tephrosia purpurea (L.) Pers. with Glomus

V. Ganesan; S. Ragupathy; B. Parthipan; D. B. Rajini Rani; A. Mahadevan

1991-01-01

285

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

Microsoft Academic Search

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

Simon M. F. Sheppard; Henry P. Schwarcz

1970-01-01

286

Calcite-graphite isotope thermometry in amphibolite facies marble, Bancroft, Ontario  

Microsoft Academic Search

This study presents calcite-graphite carbon isotope fractionations for 32 samples from marble in the northern Elzevir terrane of the Central Metasedimentary Belt, Grenville Province, southern Ontario, Canada. These results are compared with temperatures calculated by calcite-dolomite thermometry (15 samples), garnet-biotite thermometry (four samples) and garnet-hornblende thermometry (three samples). Dcal-gr values vary regularly across the area from >6.5& in the south

S. R. DUNN

2005-01-01

287

Origin of sulfate in barite and calcite cements in the Jebel Madar salt dome (Oman)  

NASA Astrophysics Data System (ADS)

Jebel Madar is a 500-m high mountain rising in the desert at the Oman Foothills. The Jebel consists of Triassic to Cretaceous carbonate host rocks forming the carapace of a salt dome. Halokinesis caused major fracturing and faulting at Jebel Madar, and the resulting structures acted as the main pathways for fluids that generated diagenetic cements composed of both barite and calcite. The spatial distribution of calcite and barite occurrences shows that calcite is formed in large abundance along the three main faults, whereas barite is more concentrated along faults further away from the three main ones. The stable carbon and oxygen isotope composition of calcite and fluid inclusion data from both calcite and barite show a distinct evolution of the fluid with a highly saline component towards more mixing with meteoric water. This is in agreement with clumped isotopes data on calcite cements indicating an evolution towards lower temperatures, consistent with doming of the Jebel and greater input of lower-temperature descending meteoric fluids. Here, we present sulphur and oxygen isotopic data on barite that suggest a link between the barite formation and the Precambrian salt underlying Jebel Madar. The average ?34S measured in barite is 33 CDT (1? = 5; n = 33), which falls at the lower end of the ?34S range reported for the Ara Group anhydrite. The average ?18O in the same barite samples is 23 VSMOW (1? = 2; n = 33). Data from the barite will be compared with sulphur isotopes from the carbonate-associate sulfate in the calcite cements. The overall goal of our research is to gain a better insight in the formation process of barite and calcite in Jebel Madar and its link with salt tectonics. We would like to acknowledge the financial support of QCCSRC (funded jointly by Qatar Petroleum, Shell and the Qatar Science & Technology Park) and the GSA Laubach fund for this study.

Vandeginste, V.; John, C. M.; Gilhooly, W. P.

2012-12-01

288

Precipitation of aragonite by calcitic bivalves in Mg-enriched marine waters  

Microsoft Academic Search

To understand the relative importance of biological versus physicochemical control over biomineralization, we have tested\\u000a if the chemical composition of the medium (i.e., the Mg\\/Ca ratio) can change the mineralogy of mollusk shells. The shells\\u000a of mollusks are made of calcite and\\/or aragonite, which are by far the most common CaCO3 polymorphs. Several species of bivalves with predominantly calcitic shells

Antonio G. Checa; Concepcin Jimnez-Lpez; Alejandro Rodrguez-Navarro; Jorge P. Machado

2007-01-01

289

Shock temperature in calcite (CaCO 3) at 95-160 GPa  

NASA Astrophysics Data System (ADS)

The temperatures induced in crystalline calcite (CaCO 3) upon planar shock compression (95-160 GPa) are reported from two-stage light gas gun experiments. Temperatures of 3300-5400 K are obtained by fitting six-channel optical pyrometer radiances in the 450-900 nm range to the Planck gray-body radiation law. Thermodynamic calculations demonstrate that these temperatures are some 400-1350 K lower than expected for vibronic excitations of the lattice with a 3 R/mole-atom specific heat ( R is gas constant). The temperature deficit along the Hugoniot is larger than that expected from only melting. In addition to melting, it appears likely that shock-induced decomposition of calcite occurs behind the shock front. We modeled disproportionation of calcite into CaO (solid) plus CO 2 (gas). For temperature calculations, specific heat at constant volume for 1 mole of CO 2 is taken to be 6.7 R as compared to 9 R in the solid state; whereas a mole of calcite and a mole of CaO have their solid state values 15 R and 6 R, respectively. Calculations suggest that the calcite decomposes to CaO and CO 2 at 11010 GPa along the Hugoniot. Recent reanalysis of earlier VISAR measurements of particle velocity profiles [1] indicates that calcite shocked to 18 GPa undergoes disproportionation at much lower pressures upon isentropic expansion.

Gupta, Satish C.; Love, Stanley G.; Ahrens, Thomas J.

2002-07-01

290

Big Seed  

NSDL National Science Digital Library

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.

2012-12-06

291

Mighty Seeds  

NSDL National Science Digital Library

In this biology experiment, learners plant soybean seeds in plaster of Paris, witnessing firsthand the mighty power and ability of plants to grow in adverse conditions. This is also an excellent activity to touch upon exothermic reactions, as warmth is created when the plaster is mixed.

Cosi

2009-01-01

292

Experimental study of the mechanism of the calcite-dolomite replacement  

NASA Astrophysics Data System (ADS)

When a mineral comes into contact with a fluid with which it is out of equilibrium, it may be replaced by a phase with a different composition and crystal structure. The reaction mechanism generally involves a coupled dissolution and precipitation mechanism and may result in a pseudomorphic replacement (Putnis, 2009). The existence of sharp limestone-dolomite contacts in natural rocks suggests that this process may operate in the course of dolomitization during burial and diagenesis. The idealized mass balance reaction is generally written as 2CaCO3+Mg2+?CaMg(CO3)2+Ca2+. However, the mechanism and environmental settings of dolomitization, are still under discussion. In order to explore the mechanism of replacement of calcite by dolomite, we performed hydrothermal experiments on marble cubes (Carrara, Italy) of different edge lengths (1.5 to 5 mm), which reacted with (Ca,Mg)Cl2 solutions of varying compositions, at temperatures between 160 and 200 C for different duration times. The product phases were identified by X-ray diffraction (XRD), Raman spectroscopy, and electron microprobe analysis (EMPA), and the textural evolution was studied by scanning electron microscopy (SEM). The results show that the amount and type of reaction strongly depend on the Mg/Ca ratio, the fluid/rock ratio, the temperature, and the reaction time. Depending on the solution composition, the reaction rims of the marble cubes are made up of several layers containing dolomite with varying textures and porosities as well as magnesite, MgCO3, in the outer rim. Fluid and mass transport along the grain boundaries controls the overall textural evolution and rate of dolomitization. The replacement reactions are pseudomorphic and take place by a coupled dissolution-precipitation mechanism. Putnis A. Mineral Replacement Reactions. In: Thermodynamics and Kinetics of Water-Rock Interaction. Oelkers E. H & Schott J (eds). Reviews in Mineralogy & Geochemistry 30, 87-124 (2009)

Moraila-Martinez, Teresita; Dunkel, Kristina G.; Putnis, Andrew; Putnis, Christine V.

2014-05-01

293

The effect of seed preparation on the chirality of the secondary nuclei  

Microsoft Academic Search

Previous secondary nucleation experiments were conducted with chiral NaClO3 crystal seeds prepared by regular cooling (1.6C\\/h). In these experiments seeds were used prepared by slow cooling (0.1C\\/day) and by evaporation. In all cases, at low supercoolings almost all the nucleated crystals have the same chirality as the seed. Above a certain supercooling, however, crystals of both chiralities are obtained. This

Ru-Ying Qian; Gregory D. Botsaris

2004-01-01

294

Bacterially Induced Calcite Precipitation and Strontium Co-Precipitation under Flow Conditions in a Porous Media System  

NASA Astrophysics Data System (ADS)

The process of in situ carbonate mineral formation has implications in many environmental applications, including, but not limited to aquifer decontamination, enhancement of soil stability, and carbon capture and storage (CCS). The high stability of carbonates and the potential for co-precipitation of contaminants within carbonates are attractive attributes for several potential engineering applications. Ureolytic precipitation of calcium and strontium carbonates by Sporosarcina pasteurii was examined in two-dimensional flat plate porous media reactors. Complete reactor plugging due to biofilm formation and calcium carbonate precipitation was achieved in Sr-free systems after 14 hours and in Sr-inclusive systems after 15 hours. Comparison of the reactor influent and effluent after 11 hours indicated that Ca2+ concentrations in the Sr-free reactor effluent were reduced to approximately 0.48% of the influent concentration while the Ca2+ and Sr2+ concentrations of the Sr-inclusive effluent were reduced to 0.64% and 2.34% of the influent concentration indicating a slight inhibitory effect of strontium on calcium carbonate precipitation . Despite this slight inhibition, more than 98% of the Ca2+ entering the reactors was precipitated. Calcite was identified as the main mineral formed and a larger mean crystal size and density were observed near the reactor influent. Homogenous partition coefficients calculated from extracted precipitates suggest higher Sr2+ partitioning near the inlet region, where higher precipitation kinetics exist. Results confirm the possibility of effective calcite-based co-precipitation of Sr2+ under flow conditions and contributes towards the development of field-scale calcium carbonate mineral-based immobilization strategies.

Gerlach, R.; Mitchell, A. C.; Schultz, L.; Cunningham, A.

2009-12-01

295

Oriented growth of cadmium telluride crystals from the vapor phase  

Microsoft Academic Search

The effect of the temperature of crystallization, the magnitude of mass transfer, and the structure of the seed crystal on the oriented growth of cadmium telluride crystals from the vapor was studied. Crystals oriented in the <110>, <111>, and <112> directions were grown in the temperature interval 1130-1330 K from the vapor of cadmium telluride crystals. The maximum possible rates

L. A. Klinkova; S. A. Erofeeva

1988-01-01

296

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

Microsoft Academic Search

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

Heather Silyn-Roberts; R. M. Sharp

1986-01-01

297

Aggregation-governed oriented growth of inorganic crystals at an organic template  

E-print Network

concentrations, while at higher concentrations the crystals self-aggregate to form linear chains and sheets,7 2PbCO3·Pb OH 2,8 etc. Oriented crystalline growth under Langmuir monolayers has been shown to stem of nanoparticle chains and sheets. Similarly, calcite crystals grown in polyacrylamide hydrogel networks aggregate

Dutta, Pulak

298

Tropical Silurian Paleotemperatures from Clumped Isotope Analysis of Coexisting Dolomite and Calcite  

NASA Astrophysics Data System (ADS)

In many instances, pervasive diagenetic alteration of original material prevents the use of quantitative climate proxies on Paleozoic or older rocks. As an inherently diagenetic phase, dolomite may provide a more resilient paleotemperature resource. The ?47 carbonate clumped isotope thermometer has been shown to be an accurate paleothermometer and, in a limited way, has been shown to be applicable to dolomites. The shallow water carbonates of the Pipe Creek Jr. Reef in central Indiana offer an opportunity to test the viability of the technique in ancient dolomite. After formation in the late Silurian, a sea level drop resulted in a diagenetic sequence of meteoric phreatic alteration of marine cement and biotic components, which included precipitation of dolomite cements inter-grown within the meteoric phreatic calcite cement. This was post-dated by a coarse void filling calcite spar formed at burial temperatures of ~100C (based on fluid inclusion analysis). Preliminary analyses of coexisting dolomite and calcite suggest that near-surface temperatures are preserved in dolomites despite having experienced elevated thermal diagenetic effects.. In contrast, co-existing early-formed calcites exhibit resetting of earth surface temperatures to elevated values. ?47 measurements in dolomites yield temperatures around 30C using the Guo et al., (2009) theoretical calibration. This contrasts with analyses of early (original) and late (hydrothermal) calcites, which record temperatures greater than ~80C using the ?47-calcite calibration of Dennis and Schrag (2010). These data support the hypothesis that dolomite can be a more resilient paleotemperature proxy relative to calcite in deep-time studies. Temperatures from dolomites compare reasonably with other late Silurian paleoclimate studies, and offer insight into regional-scale paleoclimate.

Winkelstern, I. Z.; Lohmann, K. C.

2013-12-01

299

Total immersion crystal growth  

NASA Technical Reports Server (NTRS)

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

Morrison, Andrew D. (inventor)

1987-01-01

300

Crystal Notes The Crystal  

E-print Network

Crystal Notes The Crystal The crystal is defined as an ordered set of atoms (molecules) arranged. Ordered crystals exist because in their formation they must disorder their surroundings more than they are ordered. The key to growing a crystal is to cause in the disorder of the surroundings to be more than

Meagher, Mary

301

Some Debye temperatures from single-crystal elastic constant data  

USGS Publications Warehouse

The mean velocity of sound has been calculated for 14 crystalline solids by using the best recent values of their single-crystal elastic stiffness constants. These mean sound velocities have been used to obtain the elastic Debye temperatures ??De for these materials. Models of the three wave velocity surfaces for calcite are illustrated. ?? 1966 The American Institute of Physics.

Robie, R.A.; Edwards, J.L.

1966-01-01

302

Effect of fatty acids, water composition and pH on the wettability alteration of calcite surface  

Microsoft Academic Search

Fatty acids in presence of water film alter calcite surface to oil-wet. The wettability alteration is dependent on the structure of the fatty acids, water composition and pH. Long chain fatty acid (stearic acid), strongly adsorbs onto the calcite surface from oil phase (n-C10) in oil\\/water\\/calcite system as indicated by contact angle measurements. On the other hand, short chain fatty

K. A. Rezaei Gomari; A. A. Hamouda

2006-01-01

303

Lead adsorption at the calcite-water interface: Synchrotron X-ray standing wave and X-ray reflectivity studies  

Microsoft Academic Search

By combining synchrotron X-ray standing wave (XSW) measurements with synchrotron X-ray reflectivity measurements, we have determined: (1) the precise three-dimensional location within the calcite unit cell of submonolayer Pb ions adsorbed at the calcite (104) surface from dilute aqueous solutions, and (2) the precise one-dimensional location of these unit cells relative to the calcite surface. Our XSW measurements, using three

Neil C. Sturchio; Ronald P. Chiarello; Likwan Cheng; Paul F. Lyman; Michael J. Bedzyk; Yonglin Qian; Hoydoo You; Dennis Yee; Phillip Geissbuhler; Larry B. Sorensen; Yong Liang; Donald R. Baer

1997-01-01

304

Dolomite-magnesian calcite relations at elevated temperatures and CO2 pressures  

USGS Publications Warehouse

The equilibrium thermal decomposition curve of dolomite has been determined up to a CO2 pressure of 20,000 lb/in.2, at which pressure dolomite decomposes at 857??C. Equilibrium was approached from both directions, by the breakdown and by the solid-state synthesis of dolomite. At elevated temperatures and pressures, calcites in equilibrium with periclase as well as those in equilibrium with dolomite contain Mg in solid solution. In the former, the Mg content increases with increasing CO2 pressure, and decreases with increasing temperature. In the latter, it is a function of temperature only. The exsolution curve of dolomite and magnesian calcite has been determined between 500?? and 800??C; at 500?? dolomite is in equilibrium with a magnesian calcite containing ~6 mol per cent MgCO2; at 800??, ~22 mol per cent. There appears to be a small but real deviation from the ideal 1 : 1 Ca : Mg ratio of dolomite, in the direction of excess Ca, for material in equilibrium with magnesian calcite at high temperature. The experimental findings indicate that very little Mg is stable in the calcites of sedimentary environments, but that an appreciable amount is stable under higher-temperature metamorphic conditions, if sufficient CO2 pressure is maintained. ?? 1955.

Graf, D. L.; Goldsmith, J. R.

1955-01-01

305

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

PubMed

Calcite is an important, relatively soluble mineral phase that can affect uranium reactive transport in subsurface sediments. This study was conducted to investigate the distribution of calcite and its influence on uranium adsorption and reactive transport in the groundwater-river mixing zone of the Hanford 300A site, Washington State. Simulations using a two-dimensional (2D) reactive transport model under field-relevant hydrological and hydrogeochemical conditions revealed the development of a calcite reaction front through the mixing zone as a result of dynamic groundwater-river interactions. The calcite concentration distribution, in turn, affected the concentrations of aqueous carbonate and calcium, and pH through dissolution, as river waters intruded and receded from the site at different velocities in response to stage changes. The composition variations in groundwater subsequently influenced uranium mobility and discharge rates into the river in a complex fashion. The results implied that calcite distribution and concentration are important variables that need to be quantified for accurate reactive transport predictions of uranium, especially in dynamic groundwater-river mixing zones. PMID:24240103

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

2014-01-01

306

Monitoring bacterially induced calcite precipitation in porous media using magnetic resonance imaging and flow measurements  

NASA Astrophysics Data System (ADS)

A range of nuclear magnetic resonance (NMR) techniques are employed to provide novel, non-invasive measurements of both the structure and transport properties of porous media following a biologically mediated calcite precipitation reaction. Both a model glass bead pack and a sandstone rock core were considered. Structure was probed using magnetic resonance imaging (MRI) via a combination of quantitative one-dimensional profiles and three-dimensional images, applied before and after the formation of calcite in order to characterise the spatial distribution of the precipitate. It was shown through modification and variations of the calcite precipitation treatment that differences in the calcite fill would occur but all methods were successful in partially blocking the different porous media. Precipitation was seen to occur predominantly at the inlet of the bead pack, whereas precipitation occurred almost uniformly along the sandstone core. Transport properties are quantified using pulse field gradient (PFG) NMR measurements which provide probability distributions of molecular displacement over a set observation time (propagators), supplementing conventional permeability measurements. Propagators quantify the local effect of calcite formation on system hydrodynamics and the extent of stagnant region formation. Collectively, the combination of NMR measurements utilised here provides a toolkit for determining the efficacy of a biological-precipitation reaction for partially blocking porous materials.

Sham, E.; Mantle, M. D.; Mitchell, J.; Tobler, D. J.; Phoenix, V. R.; Johns, M. L.

2013-09-01

307

Influence of calcite on uranium(VI) reactive transport in the groundwate-river mixing zone  

NASA Astrophysics Data System (ADS)

Calcite is an important, relatively soluble mineral phase that can affect uranium reactive transport in subsurface sediments. This study was conducted to investigate the distribution of calcite and its influence on uranium adsorption and reactive transport in the groundwate-river mixing zone of the Hanford 300A site, Washington State. Simulations using a two-dimensional (2D) reactive transport model under field-relevant hydrological and hydrogeochemical conditions revealed the development of a calcite reaction front through the mixing zone as a result of dynamic groundwate-river interactions. The calcite concentration distribution, in turn, affected the concentrations of aqueous carbonate and calcium, and pH through dissolution, as river waters intruded and receded from the site at different velocities in response to stage changes. The composition variations in groundwater subsequently influenced uranium mobility and discharge rates into the river in a complex fashion. The results implied that calcite distribution and concentration are important variables that need to be quantified for accurate reactive transport predictions of uranium, especially in dynamic groundwate-river mixing zones.

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

2014-01-01

308

Seed Treatment. Bulletin 760.  

ERIC Educational Resources Information Center

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)

Lowery, Harvey C.

309

Infrared spectroscopy and density functional theory investigation of calcite, chalk, and coccoliths-do we observe the mineral surface?  

PubMed

We have measured infrared spectra from several types of calcite: chalk, freshly cultured coccoliths produced by three species of algae, natural calcite (Iceland Spar), and two types of synthetic calcite. The most intense infrared band, the asymmetric carbonate stretch vibration, is clearly asymmetric for the coccoliths and the synthetic calcite prepared using the carbonation method. It can be very well fitted by two peaks: a narrow Lorenzian at lower frequency and a broader Gaussian at higher frequency. These two samples both have a high specific surface area. Density functional theory for bulk calcite and several calcite surface systems allows for assignment of the infrared bands. The two peaks that make up the asymmetric carbonate stretch band come from the bulk (narrow Lorenzian) and from a combination of two effects (broad Gaussian): the surface or near surface of calcite and line broadening from macroscopic dielectric effects. We detect water adsorbed on the high surface area synthetic calcite, which permits observation of the chemistry of thin liquid films on calcite using transmission infrared spectroscopy. The combination of infrared spectroscopy and density functional theory also allowed us to quantify the amount of polysaccharides associated with the coccoliths. The amount of polysaccharides left in chalk, demonstrated to be present in other work, is below the IR detection limit, which is 0.5% by mass. PMID:25318063

Andersson, M P; Hem, C P; Schultz, L N; Nielsen, J W; Pedersen, C S; Sand, K K; Okhrimenko, D V; Johnsson, A; Stipp, S L S

2014-11-13

310

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.

311

Method of controlling defect orientation in silicon crystal ribbon growth  

NASA Technical Reports Server (NTRS)

The orientation of twinning and other effects in silicon crystal ribbon growth is controlled by use of a starting seed crystal having a specific (110) crystallographic plane and (112) crystallographic growth direction.

Leipold, M. H. (inventor)

1978-01-01

312

Interpretation of speleothem calcite ?13C variations: Evidence from monitoring soil CO2, drip water, and modern speleothem calcite in central Texas  

NASA Astrophysics Data System (ADS)

We studied the sources and transport of carbon in two active karst systems in central Texas, Inner Space Cavern (IS) and Natural Bridge North and South Caverns (NB), to provide new insights into the interpretation of speleothem (cave calcite deposit) carbon isotope compositions. We have determined the ?13C values of soil CO2 (?13Cs) in grassland and savanna above these caves with ?13C values of cave drip water (?13CHCO3-) and modern speleothem calcite grown on artificial substrates (?13Ccc). We compare ?13CHCO3- values from direct drip sites, where water was sampled immediately upon discharging from the cave ceiling, to values from indirect sites, where water was sampled after flowing along a prolonged path within the cave that allowed for longer CO2 degassing and have found that direct drip sites yield consistently lower ?13CHCO3- values. The ?13CHCO3- values of direct drip water below savanna (-10.6 0.5 and -12.6 0.2, in NB and IS, respectively) are indistinguishable from (IS) or similar to (NB) calculated ?13CHCO3- values in equilibrium with measured soil CO2 beneath trees (-13.5 to -11.3 for juniper trees above NB, and -13.6 to -12.6 for mixed oak and elm trees above IS, respectively). At IS, the ?13CHCO3- values of direct drip water are higher below grassland (-9.7 0.3) than below savanna (12.6 0.2). These results suggest that the ?13CHCO3- values of drip waters that initially enter the caves are controlled by deep-rooted plants, where present, and are minimally influenced by host-rock dissolution and/or prior calcite precipitation (PCP). The ?13CHCO3- values of indirect drip water vary seasonally with relatively low values during the summer (-10.8 0.8 and -9.2 0.4 under juniper savanna at NB and under grassland at IS, respectively) that are similar to the direct drip ?13CHCO3- values (-10.6 0.5 and -9.7 0.3 under savanna at NB and under grassland at IS, respectively). The relatively high ?13CHCO3- values of indirect drip sites during the winter (?13CHCO3- = -8.6 0.8 at NB and 8.0 0.1 at IS) result from CO2 degassing of water along in-cave flow paths. We also present decade-long records of modern calcite ?13C values from direct and indirect drip sites at IS. The ?13Ccc values vary seasonally with lower values during the summer and higher values during the winter, and with smaller amplitude variations at the direct drip site. Such seasonal variations can be used as a geochronological tool in some speleothems that do not contain visible lamina. The summer ?13Ccc values of direct drip calcite are similar to ?13Ccc values predicted from soil CO2 collected beneath trees above that drip site. The occurrence of highest ?13Ccc values during the winter, when cave CO2 concentrations are low, highlights the significance of ventilation-driven changes in cave-air pCO2. Modern calcite ?13C values are also negatively correlated with drip rate, which suggests that ?13Ccc variations are controlled by kinetic effects during degassing and calcite precipitation associated with the drip water exposure time to a low-pCO2 environment. In all, at the caves we investigated, variability in speleothem ?13Ccc values primarily reflect presence/absence of deep-rooted vegetation and kinetic isotope effects. We therefore infer that increased aridity may result in higher ?13C values of vegetation, lower drip rates and more drip water degassing, and thus higher ?13Ccc values of speleothem calcite.

Meyer, Kyle W.; Feng, Weimin; Breecker, Daniel O.; Banner, Jay L.; Guilfoyle, Amber

2014-10-01

313

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

NASA Astrophysics Data System (ADS)

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.

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

2005-04-01

314

Uranium in foraminiferal calcite as a recorder of seawater uranium concentrations  

SciTech Connect

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 calida) foraminifera show that the U/Ca ratio of cleaned calcite tests is proportional to the concentration of uranium in solution. After correcting results for the presence of initial calcite, the apparent distribution coefficient D = (U/Ca[sub calcite])/(U/Ca)[sub solution] = 10.6 [+-] 0.3 (x10[sup [minus]3]) for A. lobifera and D = 7.9 [+-] 0.1 (x10[sup [minus]3]) for G. calida. U/Ca ratios in planktonic foraminifera from core tops collected above 3900 m in the equatorial Atlantic and above 2100 m in the Pacific Ocean show no significant difference among the species analyzed. D estimated form core top samples ranges from 7.6 [+-] 0.4 (x10[sup [minus]3]) for O. universa to 8.4 [+-] 0.5 (x10[sup [minus]3]) for G. ruber. In benthic species C. wuellerstorfi, D = 7.0 [+-] 0.8 (x10[sup [minus]3]). U/Ca and Mg/Ca in G. tumida and G. sacculifer from core tops taken near and below the regional lysocline decrease with water depth. Smaller decreases in U/Ca and Mg/Ca with depth were observed in C. wuellerstorfi. In the planktonic species, the authors believe that U/CA and Mg/Ca are lower in the more dissolution-resistant fraction of calcite, leading to lower U/Ca in more highly dissolved samples.

Russell, A.D.; Emerson, S.; Nelson, B.K. (Univ. of Washington, Seattle, WA (United States)); Erez, J. (Univ. of Jerusalem, (Israel)); Lea, D.W. (Univ. of California, Santa Barbara, CA (United States))

1994-01-01

315

Uranium in foraminiferal calcite as a recorder of seawater uranium concentrations  

NASA Astrophysics Data System (ADS)

We 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 ( Globigerinella calida) foraminifera show that the U/Ca ratio of cleaned calcite tests is proportional to the concentration of uranium in solution. After correcting results for the presence of initial calcite, the apparent distribution coefficient D = ( U/Ca) calciteU/Ca) solution = 10.6 0.3 (10 -3) for A. lobifera and D = 7.9 0.1 (10 -3) for G. calida. U/Ca ratios in planktonic foraminifera from core tops collected above 3900 m in the equatorial Atlantic and above 2100 m in the Pacific Ocean show no significant difference among the species analyzed. D estimated from core top samples ranges from 7.6 0.4 ( 10 -3) for O. universa to 8.4 0.5 (10 -3) for G. ruber. In benthic species C. wuellerstorfi, D = 7.0 0.8 (10 -3). U/Ca and Mg/Ca in G. tumida and G. sacculifer from core tops taken near and below the regional lysocline decrease with water depth. Smaller decreases in U/Ca and Mg/Ca with depth were observed in C. wuellerstorfi. In the planktonic species, we believe that U/Ca and Mg/Ca are lower in the more dissolution-resistant fraction of calcite, leading to lower U/Ca in more highly dissolved samples.

Russell, Ann D.; Emerson, Steven; Nelson, Bruce K.; Erez, Jonathan; Lea, David W.

1994-01-01

316

Seeded directional growth of superconducting bulk Y123  

NASA Astrophysics Data System (ADS)

We report a fabrication process of textured YBCO grown by seeded directional solidification using a MgO crystal as a seed, which alignes YBCO grains along c-axis with a texturing degree reduction as the distance from the seed increases. Measurements of magnetic hysteresis cycles were performed by means of vibrating sample magnetometry and the critical current density was estimated using Bean's critical state model.

Boffa, M.; Boutet, M.; Di Trolio, A.; Pace, S.; Sparvieri, N.; Testa, A. M.; Vecchione, A.

1997-08-01

317

The analysis of thermoluminescent glow peaks of natural calcite after beta irradiation.  

PubMed

In this study, the thermoluminescence properties of natural calcite samples were examined in detail. The glow curve of the sample irradiated with beta radiation shows two main peaks, P1 (at 115 C) and P4 (at 254 C). The additive dose, variable heating rate, computer glow curve deconvolution, peak shape and three point methods have been used to evaluate the trapping parameters, namely the order of kinetics (b), activation energy (E) and the frequency factor (s) associated with the dosimetric thermoluminescent glow peaks (P1 and P4) of natural calcite after different dose levels with beta irradiation. PMID:22355170

Yildirim, R Gler; Kafadar, V Emir; Yazici, A Necmeddin; Gn, Esen

2012-09-01

318

Bean Seed Imbibition.  

ERIC Educational Resources Information Center

Enables students to examine the time course for seed imbibition and the pressure generated by imbibing seeds. Provides background information, detailed procedures, and ideas for further investigation. (DDR)

Hershey, David R.

1998-01-01

319

Microstructural and textural development of calcite marbles during polyphase deformation of Penninic units within the Tauern Window (Eastern Alps)  

Microsoft Academic Search

The evolution of calcite microstructures and crystallographic preferred orientations (CPOs) is well understood due to well constrained experimental studies. However, the interpretation of naturally deformed calcite marbles is more difficult because of less constrained strain paths, a multiphase deformation history, and variable PT conditions. The Penninic units within the Tauern Window (Eastern Alps) have been affected by several deformation events

W. Kurz; F. Neubauer; W. Unzog; J. Genser; X. Wang

2000-01-01

320

Experiment Study on the Removal of Phosphorus in Eutrophic Water Bodies by the Utilization of Mineral Calcite  

Microsoft Academic Search

For seeking a new method to solve the problem of eutrophication, we have made the experiments of removing phosphorus in eutropic water by use of mineral calcite. The results indicate that the mineral calcite can remove phosphorus from the solution, and that the initial phosphorus concentration may influence the efficiency of phosphorus removal. The dephosphorization rate is high when the

Hong XU; Jing ZHANG; Yiming GAO

2008-01-01

321

New insights to cloud seeding for enhancing precipitation and hail suppression  

E-print Network

1 New insights to cloud seeding for enhancing precipitation and hail suppression Daniel Rosenfeld The modern era of cloud seeding began with the discovery of when Vincent Schaefer that dry ice or crystals to the real world and seeded supercooled layer clouds with apparent success of glaciating the cloud drops

Daniel, Rosenfeld

322

Chemistry of the calcite/water interface: Influence of sulfate ions and consequences in terms of cohesion forces  

SciTech Connect

Calcite suspensions are used to mimic the behavior of more complex cementitious systems. Therefore the characterization of calcitewater interface in strong alkaline conditions, through ionic adsorption, electrokinetic measurements, static rheology and atomic force microscopy is a prerequisite. Calcium, a potential determining ion for calcite, adsorbs specifically onto the weakly positively charged calcite surface in water. This leads to an increase of the repulsive electric double layer force and thus weakens the particle cohesion. Sulfate adsorption, made at constant calcium concentration and ionic strength, significantly increases the attractive interactions between the calcite particles despite its very low adsorption. This is attributed to a lowering of the electrostatic repulsion in connection with the evolution of the zeta potential. The linear relationship found between the yield stress and ?{sup 2} proves that the classical DLVO theory applies for these systems, contrary to what was previously observed with CSH particles under the same conditions.

Pourchet, Sylvie, E-mail: sylvie.pourchet@u-bourgogne.fr; Pochard, Isabelle; Brunel, Fabrice; Perrey, Danile

2013-10-15

323

Atomic-Scale Study of Calcite Nucleation in Calcium Oxide Rmy Besson*  

E-print Network

Atomic-Scale Study of Calcite Nucleation in Calcium Oxide Rémy Besson* Groupe de MétallurgieO-CaCO3 system appears as a good candidate in order to get better insight into these issues. Calcium oxideO. This surprising deficiency may be explained by the complex crystallography of the phase transition, which raises

Paris-Sud XI, Université de

324

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

SciTech Connect

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.

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

1995-03-15

325

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

Microsoft Academic Search

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

H.-H. STABEL

1986-01-01

326

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

SciTech Connect

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.

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

1994-03-01

327

Clast-cortex aggregates in experimental and natural calcite-bearing fault zones  

NASA Astrophysics Data System (ADS)

We investigated the formation mechanisms of rounded clast-cortex aggregates, a composite grain found in the slipping zones of faults hosted in calcite- and clay-rich rocks. The natural aggregates contain a central clast commonly made of host-rock fragments or reworked cataclasite from the slipping zone. The central clasts are surrounded by an outer cortex of calcite or clay grains a few ?m or less in size. In laboratory experiments on calcite gouges using two rotary-shear apparatus we investigated the dependence of clast-cortex aggregate formation on the applied slip rate, normal stress, total displacement and ambient humidity. Clast-cortex aggregates formed at all investigated slip rates (100?m/s to 1m/s) but only at relatively low normal stresses (?5MPa). The aggregates were better developed with increasing displacement (up to 5m) and did not form in experiments with water-dampened gouges. In the experiments, aggregates formed in low-strain regions within the gouge layers, adjacent to the highest-strain slip zones. We propose that clast-cortex aggregates in calcite-bearing slip zones form in the shallow portions of faults during shearing in relatively dry conditions, but our experiments suggest that they cannot be used as indicators of seismic slip. Formation involves clast rotation due to granular flow accompanied by accretion of fine matrix material possibly facilitated by electrostatic forces.

Rempe, Marieke; Smith, Steven A. F.; Ferri, Fabio; Mitchell, Thomas M.; Di Toro, Giulio

2014-11-01

328

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

Microsoft Academic Search

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 (19.529.5

Dirk Nrnberg; Jelle Bijma; Christoph Hemleben

1996-01-01

329

Thermally-induced grain growth of calcite marbles on Naxos Island, Greece  

Microsoft Academic Search

The island of Naxos is composed of an elliptically shaped structural and thermal dome of Miocene age. Peak metamorphic temperatures within the central migmatite complex exceeded 700 C, decreasing to about 300 C at the most distant exposures on the island. Equigranular calcite marbles which outcrop together with metapelites and metabasites over the whole island show a systematic pattern of

S. J. Covey-Crump; E. H. Rutter

1989-01-01

330

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

E-print Network

. This precipitation can lead to changes in the overall behavior of the system, such as flow alternation and soilH and alkalinity during subsurface remediation or geotechnical engineering activities. In some cases, calcite; Fujita et al., 2004] and (2) to improve soil strength for engineering purposes [DeJong et al., 2006

Hubbard, Susan

331

Dissolution of calcite in deep-sea sediments: pH and O 2 microelectrode results  

Microsoft Academic Search

We present microelectrode profiles of oxygen, pH, and porosity measured at in situ depth across the sediment-water interface from stations above and below the calcite saturation horizon in the equatorial Atlantic. Resistivity electrode data indicate that the diffusion coefficient for solutes is attenuated by nearly a factor of two within the top centimeter of the sediment lattice. Oxygen and porosity

David Archer; Steven Emerson; Clare Reimers

1989-01-01

332

Response of eleven forage species to treatment of acid soil with calcitic and dolomitic lime  

Microsoft Academic Search

The cost and difficulty of applying lime on hilly pastures or small forage fields makes it appropriate to devote attention to efficiency of lime utilization. This study evaluated effects of calcitic and dolomitic lime on yield and mineral composition of 11 forage species grown on soil with a low base status of 0.46 cmolc as Ca and 0.18 cmolc as

A. L. Pires; J. L. Ahirichs; C. L. Rhykerd

1992-01-01

333

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

Microsoft Academic Search

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,

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

2000-01-01

334

Histochemical and ultrastructural studies on Salix alba and S. matsudana seeds  

Microsoft Academic Search

Mature seeds of Salix alba L. and Salix matsudana Koidz. are exendospermous and consist of an embryo and a seed coat. Ultrastructural studies show the presence of protein bodies, lipid bodies, chloroplasts, and a nucleus in the cells of most of the embryo tissues. Protein bodies always contain two or more globoid crystals. Energy-dispersive X-ray analysis of globoid crystals revealed

Horacio Maroder; Imelda Prego; Sara Maldonado

2003-01-01

335

New insights into the carbon isotope composition of speleothem calcite from vegetation, soil, and subsurface processes  

NASA Astrophysics Data System (ADS)

The purpose of this study was to provide new insights into the interpretation of speleothem (cave calcite deposit) ?13C values. We studied two caves in central Texas, which have been actively monitored for over 12 years. We compared ?13C values of soil CO2 (?13Cs), cave drip water (?13CDIC), and modern cave calcite (?13Ccc). Measured average ?13C values of soil CO2 were -13.9 1.4 under mixed, shallowly-rooted C3-C4 grasses and were -18.3 0.7 under deeply-rooted ashe juniper trees (C3). The ?13CDIC value of minimally-degassed drip water in Natural Bridge Caverns was -10.7 0.3. The carbon isotope composition of CO2 in equilibrium with this measured drip water is -18.1 0.3. The agreement between juniper soil CO2 and drip water (within ~0.2) suggests that the ?13C value of drip water (?13CDIC) that initially enters the cave is controlled by deeply-rooted plants and may be minimally influenced by host-rock dissolution and/or prior calcite precipitation (PCP). At Inner Space Caverns, ?13CDIC values varied with vegetation above the drip site, distance from the cave entrance, and distance along in-cave flow paths. Whereas CO2 derived from deeply-rooted plants defines the baseline for drip water ?13CDIC entering the caves, kinetic effects associated with the degassing of CO2 and simultaneous precipitation of calcite account for seasonal variability in ?13CDIC and ?13Ccc. We documented increases in ?13CDIC at a rate of up to 0.47/hour during the season of peak degassing (winter), suggesting that ?13CDIC variations may be controlled by total elapsed time of CO2 degassing from drip water (exposure time, Texp). We also observed seasonal shifts in the ?13C values of modern calcite grown on glass substrates that are correlated with shifts in drip water ?13CDIC values and drip-rate. We evaluated a 10-year record of modern calcite samples and contrasted the magnitude of variability between calcite precipitated under varying pCO2 conditions and comparative length of the drip water flow paths. We propose that large variability (>2) in speleothem ?13Ccc values dominantly reflect major vegetation changes, and/or increasing Texp by slowing drip-rates under low-pCO2 conditions.

Meyer, K.; FENG, W.; Breecker, D. O.; Banner, J. L.; Guilfoyle, A.

2012-12-01

336

Modulation of calcium oxalate monohydrate crystallization kinetics in vitro  

Microsoft Academic Search

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,

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

1988-01-01

337

A model for microbially induced precipitation of vadose-zone calcites in fractures at LOS Alamos, New Mexico, USA  

NASA Astrophysics Data System (ADS)

Fractures are unique environments that can concentrate the flow of water, nutrients, and contaminants. As such, fractures play an important role in controlling the flux of various substances into and through the vadose zone. Calcite fracture fillings are present in the near surface in the Bandelier Tuff Formation at Los Alamos, New Mexico, and provide a record of the geochemical and hydrologic processes that have occurred in fractures. The objective of this study was to examine calcite fracture fills in order to improve understanding of processes within fractures, and in particular those that lead to precipitation of calcite. Samples of calcite fillings were collected from vertical and horizontal fractures exposed in a shallow waste-burial pit. Scanning electron microscopy show morphologies which suggest that plants, fungi, and bacteria were important in the precipitation process. Quadrupole mass spectrometric analyses of fluid inclusion gases show predominantly methane (17-99%) and little to no oxygen (0-8%), suggesting the development of anaerobic conditions in the fractures. Ester-linked phospholipid biomarkers are evidence for a diverse microbial community in the fractures, and the presence of di-ether lipids indicate that the methane was generated by anaerobic bacteria. The calcite fillings apparently resulted from multiple biological and chemical processes in which plant roots in the fractures were converted to calcite. Roots grew into the fractures, eventually died, and were decomposed by bacteria and fungi. Anaerobic gases were generated from encapsulated organic material within the calcite via microbial decomposition, or were generated by microbes simultaneously with calcite precipitation. It is likely that the biological controls on calcite formation that occurred in the Los Alamos fractures also occurs in soils, and may explain the occurrence of other types of pedogenic calcites.

Newman, Brent D.; Campbell, Andrew R.; Norman, David I.; Ringelberg, David B.

1997-05-01

338

Red peach and seed  

NSDL National Science Digital Library

This peach has only one large seed, as compared to the pomegranate that has many seeds. The peach is like an apple in the way that its seed is surrounded by the entire fruit. The fruit can be eaten by humans, but it is actually there as nourishment and food for the peach seed to grow.

Jack Dykinga (USDA;ARS)

1997-08-01

339

How Seeds Travel  

NSDL National Science Digital Library

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 ...

Liston, Mrs

2009-11-09

340

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

NASA Astrophysics Data System (ADS)

Field studies have suggested that calcite saturation states (mega) 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 (mega = 3, TA=2380 ?eq kg-1), two seawater reservoirs were titrated with HCl to lower their calcite saturation states (mega = 2, TA = 1910 ?eq kg-1; mega = 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 mega. This research was funded by National Science Foundation grants OCE-0351029 and OCE-0437366.

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

2006-12-01

341

Seed crystal Our Alamogordo was the biocontainment  

E-print Network

to classy restaurants and, eventually, McDonalds. Angelina Jolie became our spokesperson, and farmers burnt where to sever my brain to allow the hemispheres to rest alternately. My productivity doubled. I toyed

Loss, Daniel

342

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

343

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

NASA Astrophysics Data System (ADS)

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.

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

2008-10-01

344

Effects of increased pCO2 and geographic origin on purple sea urchin (Strongylocentrotus purpuratus) calcite elemental composition  

NASA Astrophysics Data System (ADS)

Ocean acidification will likely have negative impacts on invertebrates producing skeletons composed of calcium carbonate. Skeletal solubility is partly controlled by the incorporation of "foreign" ions (such as Mg and Sr) into the crystal lattice of these skeletal structures, a process that is sensitive to a variety of biological and environmental factors. Here we explore the effects of life stage, oceanographic region of origin, and changes in the partial pressure of carbon dioxide in seawater (pCO2) on trace elemental composition in the purple sea urchin (Strongylocentrotus purpuratus). We show that, similar to other urchin taxa, adult purple sea urchins have the ability to precipitate skeleton composed of a range of biominerals spanning low to high magnesium calcites. Mg/Ca and Sr/Ca ratios were substantially lower in adult spines compared to adult tests. On the other hand, trace elemental composition was invariant among adults collected from four oceanographically distinct regions along the US west coast (Oregon, Northern California, Central California, and Southern California). Skeletons of newly settled juvenile urchins that originated from adults from the four regions exhibited intermediate Mg/Ca and Sr/Ca between adult spine and test endmembers, indicating that skeleton precipitated during early life stages is more soluble than adult spines and less soluble than adult tests. Mean skeletal Mg/Ca or Sr/Ca of juvenile skeleton did not vary with source region when larvae were reared under present-day, global-average seawater carbonate conditions (400 ppm; pH = 8.02 0.03 1 SD; ?calcite = 3.3 0.2 1 SD). However, when reared under elevated CO2 (900 ppm; pH = 7.72 0.03; ?calcite = 1.8 0.1), skeletal Sr/Ca in juveniles exhibited increased variance across the four regions. Although larvae from the northern populations (Oregon, Northern California, Central California) did not exhibit differences in Mg or Sr incorporation under elevated CO2 (Sr/Ca = 2.09 0.06 mmol mol-1; Mg/Ca = 66.9 4.1 mmol mol-1), juveniles of Southern California origin partitioned ∼ 8% more Sr into their skeletons when exposed to higher CO2 (Sr/Ca = 2.26 0.05 vs. 2.10 0.03 mmol mol-1 1 SD). Together these results suggest that the diversity of carbonate minerologies present across different skeletal structures and life stages in purple sea urchins does not translate into an equivalent plasticity of response associated with geographic variation or temporal shifts in seawater properties. Rather, composition of S. purpuratus skeleton precipitated during both early and adult life history stages appears relatively robust to spatial gradients and predicted changes in seawater carbonate chemistry for 2100. An exception to this trend may arise during early life stages, where certain populations of purple sea urchins may alter skeletal mineral precipitation rates and composition beyond a given CO2 threshold. The degree to which this latter geochemical plasticity might affect mineral stability and solubility in a future, altered ocean requires additional study.

LaVigne, M.; Hill, T. M.; Sanford, E.; Gaylord, B.; Russell, A. D.; Lenz, E. A.; Hosfelt, J. D.; Young, M. K.

2012-12-01

345

Crystal growth by solvent evaporation and characterization of metronidazole  

NASA Astrophysics Data System (ADS)

Single crystals of metronidazole were crystallized by the slow solvent evaporation method and used as seeds to grow bulk crystals of size 8.06.52.0 mm3 using top-seeded submerged solution growth. The crystals were characterized using single crystal X-ray diffraction. Fourier transform infrared spectral analysis was made for the absorption bands of various functional groups present in the crystal. UV-vis absorption spectrum was used to identify the presence of nitroimidazole in metronidazole. Morphology study revealed that the growth is prominent along the c-axis and the prominent face is {010}. Thermal stability and thermal decomposition were analyzed using thermo calorimetry.

Ramukutty, S.; Ramachandran, E.

2012-07-01

346

CaCO3-III and CaCO3-VI, high-pressure polymorphs of calcite: Possible host structures for carbon in the Earth's mantle  

NASA Astrophysics Data System (ADS)

Calcite, CaCO3, undergoes several high pressure phase transitions. We report here the crystal structure determination of the CaCO3-III and CaCO3-VI high-pressure polymorphs obtained by single-crystal synchrotron X-ray diffraction. This new technical development at synchrotron beamlines currently affords the possibility of collecting single-crystal data suitable for structure determination in-situ at non-ambient conditions, even after multiphase transitions. CaCO3-III, observed in the pressure range 2.5-15 GPa, is triclinic, and it presents two closely related structural modifications, one, CaCO3-III, with 50 atoms in the unit cell [a=6.281(1) , b=7.507(2) , c=12.516(3) , ?=93.76(2), ?=98.95(2), ?=106.49(2), V=555.26(20) 3 at 2.8 GPa], the second, CaCO3-IIIb, with 20 atoms [a=6.144(3) , b=6.3715(14) , c=6.3759(15) , ?= 93.84(2), ?=107.34(3), ?=107.16(3), V=224.33(13) 3 at 3.1 GPa]. Different pressure-time experimental paths can stabilise one or the other polymorph. Both structures are characterised by the presence of non-coplanar CO3 groups. The densities of CaCO3-III (2.99 g/cm3 at 2.8 GPa) and CaCO3-IIIb (2.96 g/cm3 at 3.1 GPa) are lower than aragonite, in agreement with the currently accepted view of aragonite as the thermodynamically stable Ca-carbonate phase at these pressures. The presence of different cation sites, with variable volume and coordination number (7-9), suggests however that these structures have the potential to accommodate cations with different sizes without introducing major structural strain. Indeed, this structure can be adopted by natural Ca-rich carbonates, which often exhibit compositions deviating from pure calcite. Mg-calcites are found both in nature (Frezzotti et al., 2011) and in experimental syntheses at conditions corresponding to deep subduction environments (Poli et al., 2009). At these conditions, the low pressure rhombohedral calcite structure is most unlikely to be stable, and, at the same time, Mg and Fe solubility in aragonite is hindered energetically in the 9-fold coordination site. Above 15 GPa, and up to the maximum pressure investigated (40 GPa), we observe the high-pressure polymorph CaCO3-VI, triclinic [a=3.3187(12) , b=4.8828(14) , c=5.5904(14) , ?=103.30(2), ?=94.73(2), ?=89.21(2), V=87.86(20) 3 at 30.4 GPa] with 10 atoms in the unit cell. It is characterised by coplanar CO3 groups but the structure is no longer layered, as in the lower pressure polymorphs. The density of the CaCO3-VI structure (3.78 g/cm3 at 30.4 GPa) is higher than aragonite. For this reason it could be supposed that a region may exist where this polymorph replaces aragonite in the Earth's intermediate mantle. The lower coordination number for the Ca site [7+2] instead of [9] in aragonite suggests that this structure could be easily adopted by an extended solid-solution range from calcite towards the dolomite [CaMg(CO3)2]-ankerite [CaFe(CO3)2] compositional join. The transitions from calcite to CaCO3-III, CaCO3-IIIb and CaCO3-VI are perfectly reversible and after pressure release we always observe the calcite structure, with the sample recovered as a single-crystal. Indeed, it is highly unlikely that these structures can be observed in samples recovered from high-pressure environments.

Merlini, M.; Hanfland, M.; Crichton, W. A.

2012-06-01

347

Stress and Temperature Dependence of Calcite Twinning: New Experimental and Field Constraints  

NASA Astrophysics Data System (ADS)

In low-grade metamorphic terrains at temperatures < 300 C e-twinning of calcite is common. The width and density of e-twins have been suggested to indicate stress and temperature representing robust paleopiezometers and geothermometers. To evaluate the stress- and temperature dependence of e-twins in calcite we have performed a series of deformation experiments on specimens of Carrara marble. 14 experiments were performed at 100-400 MPa confining pressure and T < 350 C in a Paterson-type gas deformation apparatus. Seven samples were deformed in axial compression test at strain rates from 10-4 -10-6s-1. Seven samples were deformed in torsion tests to shear strains ? < 1.8. After testing, thin sections of all samples were prepared for optical inspection of twin density and twin width. Twin density varied between 10 and 500 [twins/mm] at stresses up to 280 MPa. At given conditions and with increasing strain twin density increased significantly. No clear dependence of twin density on temperatures up to 300 C was found in experiments. The experimentally deformed samples were compared to naturally-deformed low-grade calcite rocks from different fault zones. From optical thin sections of 20 samples deformation temperatures were estimated based on twin width and fluid inclusion data. These samples were subsequently used for optical measurements of twin density. Twin density varied between 10 and 100 [twins/mm] up to temperatures of 300 C. Using published calcite piezometers (Rowe and Rutter 1990) we estimated paleostresses. From our experiments and field data we did not observe a clear relation between twin width and temperature up to 250 C. Above 250 C, temperatures estimated from calcite twin widths in naturally deformed calcite samples do correspond to temperatures estimated using other methods (e.g. fluid inclusion analysis, vitrinite reflection, conodont colour alteration index). Using the existing paleopiezometres, differential stresses inferred from twin density in the experimentally deformed samples are commonly overestimated by up to a factor of 2 at low stress. Towards higher stresses > 150 MPa predicted and experimental values converge for samples deformed to similar strains. The experimental data clearly shows a strong dependence of twin density on strain for all tested temperatures.

Rybacki, E.; Janssen, C.; Dresen, G.

2008-12-01

348

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

USGS Publications Warehouse

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.

Coplen, T.B.

2007-01-01

349

Method of making single crystal fibers  

NASA Technical Reports Server (NTRS)

Single crystal fibers are made from miniature extruded ceramic feed rods. A decomposable binder is mixed with powders to inform a slurry which is extruded into a small rod which may be sintered, either in air or in vacuum, or it may be used in the extruded and dried condition. A pair of laser beams focuses onto the tip of the rod to melt it thereby forming a liquid portion. A single crystal seed fiber of the same material as the feed rod contacts this liquid portion to establish a zone of liquid material between the feed rod and the single crystal seed fiber. The feed rod and the single crystal feed fiber are moved at a predetermined speed to solidify the molten zone onto the seed fiber while simultaneously melting additional feed rod. In this manner a single crystal fiber is formed from the liquid portion.

Westfall, Leonard J. (inventor)

1990-01-01

350

An AFM investigation of the interaction of chiral amino acids with the {l_brace}104{r_brace} face of calcite  

SciTech Connect

In biomineralized tissue, Nature often uses a single crystal system to form tools with widely varied form and functionality. To accomplish this, organisms have developed methods to deterministically modify and control crystal habit, commonly creating shapes with lower symmetry than is possessed by the pure crystal. In this paper we use atomic force microscopy to investigate the effect of chiral amino acids on calcite growth. We show that the atomic steps and resultant macroscopic shape exhibit a lower symmetry that reflects the chirality of the amino acid. We use this result to constrain the possible stereospecific binding sites. We argue that the change in morphology is not due to the incorporation of the amino acid, but rather that it acts like a surfactant changing the energetics of the interface. These results suggest that the conventional paradigm for understanding the geometrical and chemical aspects of biomineralization in terms of stereochemical recognition should be expanded to capture the energetic controls that determine the mechanisms of mineral modification by biomolecules.

Orme, C A; Noy, A; McBride, M T; DeYoreo, J J

2000-10-01

351

Substrate templating guides the photoinduced reaction of C60 on calcite.  

PubMed

A substrate-guided photochemical reaction of C60 fullerenes on calcite, a bulk insulator, investigated by non-contact atomic force microscopy is presented. The success of the covalent linkage is evident from a shortening of the intermolecular distances, which is clearly expressed by the disappearance of the moir pattern. Furthermore, UV/Vis spectroscopy and mass spectrometry measurements carried out on thick films demonstrate the ability of our setup for initiating the photoinduced reaction. The irradiation of C60 results in well-oriented covalently linked domains. The orientation of these domains is dictated by the lattice dimensions of the underlying calcite substrate. Using the lattice mismatch to deliberately steer the direction of the chemical reaction is expected to constitute a general design principle for on-surface synthesis. This work thus provides a strategy for controlled fabrication of oriented, covalent networks on bulk insulators. PMID:24692299

Lindner, Robert; Rahe, Philipp; Kittelmann, Markus; Gourdon, Andr; Bechstein, Ralf; Khnle, Angelika

2014-07-21

352

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

E-print Network

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.

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

2006-01-01

353

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

USGS Publications Warehouse

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.

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

1992-01-01

354

Uranium immobilization by sulfate-reducing biofilms grown on hematite, dolomite, and calcite.  

SciTech Connect

Biofilms of sulfate-reducing bacteria Desulfovibrio desulfuricans G20 wereused to reduce dissolved U(VI)and subsequently immobilize U(IV) in the presence of uranium-complexing carbonates. The biofilms were grown in three identically operated fixed bed reactors, filled with three types of minerals: one noncarbonate-bearing mineral(hematite) and two carbonate-bearing minerals (calcite and dolomite). The source of carbonates in the reactors filled with calcite and dolomite were the minerals, while in the reactor filled with hematite it was a 10 mM carbonate buffer, pH 7.2, which we added to the growth medium. Our five-month study demonstrated that the sulfate-reducing biofilms grown in all reactors were able to immobilize/reduce uranium efficiently, despite the presence of uranium-complexing carbonates.

Marsili, E.; Beyenal, Haluk; Di Palma, L.; Merli, C.; Dohnalkova, Alice; Amonette, James E.; Lewandowski, Zbigniew

2007-12-15

355

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

USGS Publications Warehouse

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.

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

1981-01-01

356

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

SciTech Connect

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.

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

2011-01-01

357

Oxygen isotopes in meteoric calcite cements as indicators of continental paleoclimate  

SciTech Connect

Because meteoric water {delta}{sup 18}O (dO) values decrease with decreasing ambient temperature and increasing latitude, dO values of meteoric calcite cement should exhibit a similar relation with paleolatitude and be an indicator of continental paleotemperatures. To test this, the authors compiled isotopic and paleolatitude data for 20 meteoric cements and nine speleothems ranging in age from Devonian to modern and in paleolatitude from 3.5{degree} to 83{degree}. The dO vs. latitude trend for these carbonates is almost identical to that predicted for modern inland environments, but differs from the trend for coastal environments. It is assumed that the modern meteoric water dO vs. temperature relation is valid for the past and that insignificant evaporation occurred prior to carbonate precipitation, then coastal and inland paleotemperatures can be calculated from the dO values of meteoric calcite (dO{sub mcl}) and seawater (dO{sub sw}) by using the equations T{sub coastal} = 13.3 {plus minus} 32.6({minus}0.231 {minus} 0.0613(dO{sub mcl} + dO{sub sw})){sup 1/2} and T{sub inland} = 17.8 {plus minus} 16.2({minus}0.572 {minus} 0.1233(dO{sub mcl} + dO{sub sw})){sup 1/2}, where T is temperature {degree}C. Calcite precipitated from coastal meteoric water at temperatures between 0 and 25{degree}C will exhibit a narrow range in dO ({minus}6% to {minus}4%, where dO{sub sw} = 0%). The dO of calcite precipitated from inland meteoric water will be sensitive to paleotemperature, ranging from {minus}14% to {minus}5% (where dO{sub sw} = 0%) for temperatures of 0 to 25{degree}C.

Hays, P.D.; Grossman, E.L. (Texas A and M Univ., College Station (USA))

1991-05-01

358

Strontium isotope geochemistry of anhydrites and calcite pseudomorphs after anhydrite from Palaeozoic formations in Belgium  

Microsoft Academic Search

Anhydrite and calcite pseudomorphs after anhydrite from Palaeozoic formations in Belgium have been analysed for their Sr isotope compositions. All Givetian (3 samples: ?0.7080) and Visean (6 samples: ?0.7076) anhydrites have 87Sr\\/86Sr ratios close to the seawater value at their deposition time which implies a marine origin for the Sr. In contrast, Frasnian anhydrite from Soumagne has a significantly higher

Lon Dejonghe; Daniel Demaiffe; Dominique Weis

1998-01-01

359

Oxygen isotope evolution of biogenic calcite and apatite during the Middle and Late Devonian  

Microsoft Academic Search

Oxygen isotope ratios of well-preserved brachiopod calcite and conodont apatite were used to reconstruct the palaeotemperature history of the Middle and Late Devonian. By assuming an oxygen isotopic composition of ?1 V-SMOW for Devonian seawater, the oxygen isotope values of Eifelian and early Givetian brachiopods and conodonts give average palaeotemperatures ranging from 22 to 25C. Late Givetian and Frasnian palaeotemperatures

M. M. Joachimski; R. van Geldern; S. Breisig; W. Buggisch; J. Day

2004-01-01

360

Kinetic parameters, bleaching and radiation response of thermoluminescence glow peaks separated by deconvolution on Korean calcite  

NASA Astrophysics Data System (ADS)

Calcite has been of particular interest in studies of thermoluminescence (TL) because of its geological and archeological importance. Although extensive research on the TL glow curves of calcite has been conducted, most previous works have been based on the TL intensity integrated over a particular temperature range on the glow curve, without any separation of peaks. In this paper, the physical characteristics of the overlapping peaks in the TL glow curves of a calcite sample are investigated. These properties can provide useful information for determining the radiation dose absorbed to the sample in radiation dosimetry and luminescence dating research. The Tm-Tstop method is employed to identify the number of hidden glow peaks, and the kinetic parameters of each separated glow peak, including the thermal activation energy, kinetic order, and frequency factor, are evaluated using a computerized glow curve deconvolution (CGCD) method. The Tm-Tstop method indicates that the glow curve of calcite is the superposition of at least four components (P1 - P4) in the temperature range between room temperature and 450 C. A bleaching experiment for two separated glow peaks (P3 and P4) using a solar simulator revealed that the bleaching rates of peak P3 show two exponential decays, and after bleaching, the TL intensity of peak P3 is reduced to approximately 4% of the initial value. In contrast, peak P4 is bleached exponentially to approximately 30% of the initial TL intensity and thereafter shows no detectable change in intensity. In addition, in a study of the radiation dose response of the two peaks, both peaks have a similar pattern, exhibiting a linear increment up to the maximum dose investigated, 520 Gy.

Kim, Ki-Bum; Hong, Duk-Geun

2014-10-01

361

Oxygen isotopes in meteoric calcite cements as indicators of continental paleoclimate  

Microsoft Academic Search

Because meteoric water δ¹⁸O (dO) values decrease with decreasing ambient temperature and increasing latitude, dO values of meteoric calcite cement should exhibit a similar relation with paleolatitude and be an indicator of continental paleotemperatures. To test this, the authors compiled isotopic and paleolatitude data for 20 meteoric cements and nine speleothems ranging in age from Devonian to modern and in

Phillip D. Hays; Ethan L. Grossman

1991-01-01

362

Monitoring Crystal Growth From Solution  

NASA Technical Reports Server (NTRS)

Experimental system for monitoring growth of triglycine sulfate (TGS) crystals from solution is being studied. System consists of outer cell containing distilled water heated and stirred to maintain constant temperature to within plus or minus 0.1 degrees C, inner (growth) cell containing supersaturated solution of TGS, and seed crystal mounted in plastic-covered stainless-steel sting equiped with controlled cooling mechanism and temperature sensors.

Lal, R. B.

1982-01-01

363

Biomimetic synthesis of coexistence of vaterite-calcite phases controlled by histidine-grafted-chitosan  

NASA Astrophysics Data System (ADS)

Biomimetic synthesis vaterite is promising in improving the application of calcium carbonate and providing a novel method for controlling synthesis other biomaterials. For the first time, the histidine-grafted-chitosan (NHCS) is used as an organic matrix to biomimetic synthesis of calcium carbonate. Effect of the pH value on the morphology and polymorph is investigated. The products are characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and field-emission scanning electron microscope (FESEM). The results show that the sole rhombohedral calcite phase can form in absence of NHCS, whereas the coexistence of vaterite-calcite phases is gained in the presence of NHCS. At pH=8.0, the content of vaterite reaches 93.7 wt%, but it drops to 62.2 wt% at pH 6.5. In addition, a possible mechanism is proposed to explain the formation of coexistence of vaterite-calcite phases in the study. The result indicates that NHCS is an effective template and pH responsive for biomimetic synthesis of vaterite, and offers a novel method for controlling synthesis of other biomaterials.

Chen, Zhangxu; Xin, Meihua; Li, Mingchun; Xu, Jianpeng; Li, Xianxue; Chen, Xiaodong

2014-10-01

364

An atomic force microscopy study of the dissolution of calcite in the presence of phosphate ions  

NASA Astrophysics Data System (ADS)

Dissolution of calcite in the presence of phosphate solutions was studied in situ by Atomic Force Microscopy. Results of experiments in slightly alkaline (NH4)2HPO4 solutions showed that dissolution, measured from etch pit spreading, is significantly reduced compared to that observed in pure deionized water, confirming an inhibitory effect of (NH4)2HPO4 on calcite dissolution. However, rates measured in the presence of Na-phosphate solutions at the same pH remained close to that in pure water. This would indicate that the inhibitory effect could be caused by the presence of the NH4+ group. Moreover, for phosphate solution concentrations >5 mM, the precipitation of a calcium phosphate phase occurred simultaneously while calcite was dissolving, despite the continuous flow of the reaction solution. Such reactions may play an important role in phosphorus recovery from P-bearing solutions. Importantly this study gives insights into the mechanism of interface-coupled dissolution-precipitation reactions occurring during the interaction of phosphate-bearing solutions with calcium carbonate minerals and emphasizes the importance of performing direct observations when determining the kinetics of dissolution reactions, as they can be significantly affected by the precipitation of secondary phases that could alter dissolution rates determined from measurements of bulk solution composition.

Klasa, J.; Ruiz-Agudo, E.; Wang, L. J.; Putnis, C. V.; Valsami-Jones, E.; Menneken, M.; Putnis, A.

2013-09-01

365

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

NASA Astrophysics Data System (ADS)

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.

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

2003-08-01

366

Intermediate-scale tests of sodium interactions with calcite and dolomite aggregate concretes. [LMFBR  

SciTech Connect

Two intermediate-scale tests were performed to compare the behavior of calcite and dolomite aggregate concretes when attacked by molten sodium. The tests were performed as part of an interlaboratory comparison between Sandia National Laboratories and Hanford Engineering Development Laboratories. Results of the tests at Sandia National Laboratories are reported here. The results show that both concretes exhibit similar exothermic reactions with molten sodium. The large difference in reaction vigor suggested by thermodynamic considerations of CO/sub 2/ release from calcite and dolomite was not realized. Penetration rates of 1.4 to 1.7 mm/min were observed for short periods of time with reaction zone temperatures in excess of 800/sup 0/C during the energetic attack. The penetration was not uniform over the entire sodium-concrete contact area. Rapid attack may be localized due to inhomogeneities in the concrete. The chemical reaction zone is less then one cm thick for the calcite concrete but is about seven cm thick for the dolomite concrete.

Randich, E.; Acton, R.U.

1983-09-01

367

Numerical Simulations of Urea Hydrolysis and Calcite Precipitation in Porous Media Using STOMP  

SciTech Connect

Subsurface radionuclide and trace metal contaminants throughout the U.S. Department of Energy (DOE) complex pose one of DOEs greatest challenges for long-term stewardship. One promising in situ immobilization approach of these contaminants is engineered mineral (co)precipitation of calcite driven by urea hydrolysis that is catalyzed by enzyme urease. The tight nonlinear coupling among flow, transport, reaction and reaction-induced property changes of media of this approach was studied by reactive transport simulations with systematically increasing level of complexities of reaction network and physical/chemical heterogeneities using a numerical simulator named STOMP. Sensitivity studies on the reaction rates of both urea hydrolysis and calcite precipitation are performed via controlling urease enzyme concentration and precipitation rate constant according to the rate models employed. We have found that the rate of ureolysis is a dominating factor in the amount of precipitated mineral; however, the spatial distribution of the precipitates depends on both rates of ureolysis and calcite precipitation. A maximum 5% reduction in the porosity was observed within the simulation time period of 6 pore volumes in our 1-dimensional (1D) column simulations. When a low permeability inclusion is considered in the 2D simulations, the altered flow fields redistribute mineral forming constituents, leading to a distorted precipitation reaction front. The simulations also indicate that mineral precipitation occurs along the boundary of the low permeability zone, which implies that contaminants in the low permeability zone could be encapsulated and isolated from the flow paths.

Luanjing Guo; Hai Huang; Bill X. Hu

2010-11-01

368

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

PubMed

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

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

2013-12-01

369

Pore-scale controls on calcite dissolution rates from flow-through laboratory and numerical experiments.  

PubMed

A combination of experimental, imaging, and modeling techniques were applied to investigate the pore-scale transport and surface reaction controls on calcite dissolution under elevated pCO2 conditions. The laboratory experiment consisted of the injection of a solution at 4 bar pCO2 into a capillary tube packed with crushed calcite. A high resolution pore-scale numerical model was used to simulate the experiment based on a computational domain consisting of reactive calcite, pore space, and the capillary wall constructed from volumetric X-ray microtomography images. Simulated pore-scale effluent concentrations were higher than those measured by a factor of 1.8, with the largest component of the discrepancy related to uncertainties in the reaction rate model and its parameters. However, part of the discrepancy was apparently due to mass transport limitations to reactive surfaces, which were most pronounced near the inlet where larger diffusive boundary layers formed around grains and in slow-flowing pore spaces that exchanged mass by diffusion with fast flow paths. Although minor, the difference between pore- and continuum-scale results due to transport controls was discernible with the highly accurate methods employed and is expected to be more significant where heterogeneity is greater, as in natural subsurface materials. PMID:24865463

Molins, Sergi; Trebotich, David; Yang, Li; Ajo-Franklin, Jonathan B; Ligocki, Terry J; Shen, Chaopeng; Steefel, Carl I

2014-07-01

370

Inside a Seed  

NSDL National Science Digital Library

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.

2007-12-12

371

Inside a Seed  

NSDL National Science Digital Library

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 embryo's primary root, cotyledon, and embryonic leaves.

Foundation, Wgbh E.

2003-09-26

372

Evaluating Cotton Seed Quality  

E-print Network

, treated and bagged for planting the following season. Producers who plan to save seed from conventional varieties are advised to evaluatr seed quality before the planting season, using procedures such as the free fatty acid test, germination tests...

Boman, Randy

2005-10-05

373

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

E-print Network

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...

Piper, Jennifer

2012-02-14

374

Stable isotopes in benthic foraminiferal calcite from a river-influenced Arctic marine environment, Kara and Pechora Seas  

E-print Network

Stable isotopes in benthic foraminiferal calcite from a river-influenced Arctic marine environment, USA Vladimir Stanovoy Arctic and Antarctic Research Institute, St. Petersburg, Russia David J in sedimentation. INDEX TERMS: 4207 Oceanography: General: Arctic and Antarctic oceanography; 4219 Oceanography

Howat, Ian M.

375

Needs of Seeds  

ERIC Educational Resources Information Center

The "Needs of Seeds" formative assessment probe can be used to find out whether students recognize that seeds have needs both similar to and different from plants and other living organisms (Keeley, Eberle, and Tugel 2007). The probe reveals whether students overgeneralize the needs of seeds by assuming they have the same needs as the adult plants

Keeley, Page

2011-01-01

376

SEED Database Requirements  

Microsoft Academic Search

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

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

377

Life on the margin: implications of ocean acidification on Mg-calcite, high latitude and cold-water marine calcifiers  

Microsoft Academic Search

Future anthropogenic emissions of CO2 and the resulting ocean acidification may have severe consequences for marine calcifying organisms and ecosystems. Marine calcifiers depositing calcitic hard parts that contain significant concentrations of magnesium, i.e. Mg-calcite, and calcify- ing organisms living in high latitude and\\/or cold-water environments are at immediate risk to ocean acidification and decreasing seawater carbonate saturation because they are

Andreas J. Andersson; Fred T. Mackenzie; Nicholas R. Bates

2008-01-01

378

Quartz crystal growth  

DOEpatents

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.

Baughman, Richard J. (Albuquerque, NM)

1992-01-01

379

The Dependence of Secondary Structure in X-Ray Absorption on Crystal Form  

Microsoft Academic Search

An examination of the Ca K absorption edge in the x-ray absorption spectra of different compounds shows clearly that the secondary structure is not the same in different compounds, and is not even the same in the two crystals calcite and aragonite, which are the same chemically, but of different crystalline form. These facts are in accord with Kronig's theory

Vola P. Barton; Geo A. Lindsay

1934-01-01

380

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

SciTech Connect

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.

Warburton, J.A.

1990-10-01

381

Fluid inclusions in quartz crystals from South-West Africa.  

NASA Technical Reports Server (NTRS)

Quartz crystals from calcite veins of unknown age in Precambrian metasedimentary rocks at Geiaus No. 6 and Aukam farms in South-West Africa contain both primary and secondary inclusions filled with one substance or a combination of substances. These substances include organic liquid, moderately saline aqueous liquid, dark-colored solid, and a vapor. Analysis of these materials by microscopy and by gas chromatography and mass spectrometry shows the presence of constituents of both low and high molecular weights.

Kvenvolden, K. A.; Roedder, E.

1971-01-01

382

7 CFR 201.15 - Weed seeds.  

Code of Federal Regulations, 2010 CFR

...Labeling Agricultural Seeds 201.15 Weed seeds. The percentage of weed seeds shall include seeds of plants considered weeds in the State into which the seed...transported and shall include noxious weed seeds. [5 FR 31, Jan. 4,...

2010-01-01

383

The nature of groundwater flow in fractured rock: Evidence from the isotopic and chemical evolution of recrystallized fracture calcites from the Canadian Precambrian Shield  

NASA Astrophysics Data System (ADS)

The isotope geochemistry of fracture calcites in three Precambrian plutons on the Canadian Shield has been investigated in order to understand the paleohydrogeological conditions in fractured crystalline rock. Fracture calcites of ancient hydrothermal origins in the Chalk River and East Bull Lake plutons exhibit 18O enrichment and 13C depletion trends resulting from recent low-temperature calcite recrystallization under open-system conditions for oxygen, but semiclosed for carbon, and under extremely variable time-integrated, water/rock (calcite) ratios. This process causes recycling of elements with calcite distribution coefficients > 1 (rare earths, manganese, and possibly iron) from the precursor calcite to younger calcites as well as calcite control over the 87Sr /86Sr ratio of the groundwater within the Chalk River pluton. The large but variable water/rock (calcite) mole ratios calculated from the shifts in the stable isotopic compositions of fracture calcites are compatible with fracture flow models that invoke flow channeling within single fractures that also contain regions of immobile porosity. Quantification of isotopic shifts resulting from recrystallization requires that the initial isotopic composition of the precursor hydrothermal calcite be well constrained. Unlike the Chalk River and East Bull Lake plutons, hydrothermal fracture calcites in the White Lake pluton, which intrudes marble-rich country rocks of the Grenville Supergroup, have highly variable ? 13C and ? 18O values. This is attributed to mixing of carbon from magmatic and sedimentary reservoirs, and to oxygen isotopic exchange between hydrothermal fluids and carbonate country rocks at the time of intrusion. Convective circulation of meteoric groundwater from the surrounding 13C-rich carbonate rocks (up to 6.6%.) resulted in ? 13C values as heavy as 3.0%. for the fracture calcites in the pluton.

Bottomley, Dennis J.; Veizer, Jn

1992-01-01

384

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

Microsoft Academic Search

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 2070 ?m. Particular attention was paid to the

Iwao Hachiya; Tetsuo Koyano; Kiyotaka Sato

1989-01-01

385

Imaging crystal orientations in multicrystalline silicon wafers via photoluminescence  

E-print Network

Imaging crystal orientations in multicrystalline silicon wafers via photoluminescence H. C. Sio, Z-mediated nonclassical crystal growth of sodium fluorosilicate nanowires and nanoplates AIP Advances 1, 042165 (2011) Crystal phase and growth orientation dependence of GaAs nanowires on NixGay seeds via vapor

386