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Showing 1 to 20 of 95 for “"aragonite"”.
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Biochemical approaches to investigate biomineralization of magnesium calcite and aragonite
… three anhydrous polymorphs, namely, the calcite, aragonite and vaterite. Of these, marine organisms generally employ either calcite (usually with small amounts of magnesium ions replacing Ca2+ ions in the lattice) or aragonite form of the mineral. This thesis is focused on understanding the …
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Calcite Cementation of Sixty-Five-Year-Old Aragonite Sand Dredge Pile
… 1942 produced four dredge piles of cross-bedded aragonite skeletal sand. The spoils piles are on the leeward (western) shore of the island, where they are subject to minimal wave energy. Collectively they are 350 x 50 m in plan view and 2 m high. The surface is very well cemented, which requires …
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An examination of trace element concentrations across calcite/aragonite transitions in a Madagascan stalagmite
Calcite and aragonite speleothems have been used for the past few decades to provide paleoclimate information, but in speleothems of mixed mineralogy the signal of mineral changes can complicate understanding of climate signals also present. This mineral signal must therefore be examined and …
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Variations in coral reef net community calcification and aragonite saturation state on local and global scales
… (NCC) to ocean acidification (OA) and declining aragonite saturation state (Ωa) requires a thorough understanding of controls on NCC. The diurnal control of light and net community production (NCP) on NCC confounds the underlying control of Ωa on NCC and must be averaged out in order to predict …
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Variations in coral reef net community calcification and aragonite saturation state on local and global scales
… (NCC) to ocean acidification OA and declining aragonite saturation state [Omega]a requires a thorough understanding of controls on NCC. The diurnal control of light and net community production (NCP) on NCC confounds the underlying control of [Omega]a on NCC and must be averaged out in order to …
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The aqueous aragonite to calcite transformation: rate, mechanisms, and its role in the development of neomorphic fabrics
The rate of the aqueous transformation of aragonite to calcite was measured at 50°, 77°, and 101°C. The observed mole fraction calcite versus time relationship can be fit by the integrated rate model: t = [(3/C₂)(1-X)2/3 + (3/C₁)(X2/3)/[K₂-K₁] The constants C₁ and C₂ combine geometric factors, …
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The Combined Effect of Ocean Acidification and Euthrophication on water pH and Aragonite Saturation State in the Northern Gulf of Mexico
… 2011 Mississippi River flood on coastal pH and aragonite saturation states. Data from a model simulation using data collected from the northern Gulf of Mexico indicates that eutrophication is contributing to acidification of subsurface waters and plays a larger role than acidification from …
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The mineralogy and chemistry of modern shallow-water and deep-sea corals
… of coral skeletons built from the mineral aragonite (CaCO3). Coral reefs are currently being threatened by ocean acidification (OA), which may lower calcification rates, reduce skeletal density, and increase aragonite dissolution. Crystallography and chemistry are what govern the materials …
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Hierarchical Assembly Strategy and Multiscale Structural Origin of Exceptional Mechanical Performance In Nacre
… nacre is assembled via epitaxial growth and the aragonite platelets are pure single-crystals. Our results challenge this conclusion and propose that nacre's individual aragonite platelets are constructed with highly-aligned aragonite nanoparticles mediated by screw dislocation and amorphous …
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The mineralogy and chemistry of modern shallow-water and deep-sea corals
… of coral skeletons built from the mineral aragonite (CaCO3). Coral reefs are currently being threatened by ocean acidification (OA), which may lower calcification rates, reduce skeletal density, and increase aragonite dissolution. Crystallography and chemistry are what govern the materials …
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Mechanical behavior of ultrastructural biocomposites
… mollusks, and consists of an inorganic phase of aragonite tablets 5-8jim in planar dimension and 0.5-1gm in thickness direction and an organic phase of biomacromolecules. High resolution microscopy imaging was employed to investigate the microscale features of seashell nacre to reveal the …
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Modeling Departures From Abiotic Expectations During the Calcium Carbonate Precipitation Process
… the carbon and oxygen isotopic composition of aragonite and coexisting spring water; and modeling these experimental results to establish whether precipitation and isotopic fractionation are consistent with abiotic CaCO3 mineralization or better explained via alternative processes. At an …
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Environmental controls on the skeletal mineralogy of marine calcifiers
… CaCO3 polymorphs used by marine calcifiers are aragonite and calcite. In the abiotic precipitation of CaCO3, the Mg/Ca ratio and the temperature are established controls of polymorph formation, but the importance of other factors, for example salinity, remains uncertain. The first objective of …
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Coral skeleton density banding: biotic response to changes in sea surface temperature
Density bands in the CaCO3 (aragonite) skeleton of scleractinian corals are commonly used as chronometers, where crystalline couplets of high and low density bands represent the span of one year. Isotopic analysis of these density bands provides a sensitive reconstructive tool for paleoclimatology …
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Uncovering the role of biomineralisation in otolith trace element uptake by microstructural and microchemical analysis
… elemental incorporation, the orientation of aragonite and the organic matrix in otoliths of four marine species were investigated in conjunction with the otolith growth patterns and the distribution of trace and minor elemental composition. Results for otoliths of Platycephalus bassensis, …
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GEOCHEMISTRY AND PETROGRAPHY OF SPELEOTHEMS FROM TURKEY AND IRAN: PALAEOCLIMATE AND DIAGENESIS
… In this study, U/Pb methods were used to date an aragonite layer in a speleothem from Iran, following the use of autoradiography to select samples with appropriately high uranium. Aragonite is metastable at earth surface conditions, and is therefore prone to recrystallisation as calcite if it …
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Fracture of the interlayer junction of the shell from a deep-sea hydrothermal vent gastropod
… The multilayer was composed of an inner, aragonite-like layer and a middle, compliant layer with a gradient layer between the two exhibiting a non-uniform composition and structure. It was found that the hardness of the middle, compliant layer was 0.186±0.007 GPa, while the inner, …
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Seasonal and interannual variability of the marine carbonate system at the ice shelf in the eastern Weddell Gyre and its sensitivity to future ocean acidification
… resulting in possible surface water wintertime aragonite (the more soluble form of calcium carbonate) undersaturation (Ωarag< 1) south of the Antarctic Polar Front by the year 2030 (McNeil and Matear, 2008). An Ocean Acidification study was conducted to determine the seasonal and interannual …
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Basic studies for the incorporation of uranium in sediments
… were carried out with lake sediment and aragonite samples. All experiments were conducted using the uranium isotope 232U under ambient pressure and room temperature at different pH. Sediment samples were obtained from an artificial lake (Willersinnweiher, SW Germany). This lake has …
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