Calcium carbonate biominerals are frequently analysed in materials science due to their abundance, diversity and unique material properties. Aragonite nacre is intensively studied, but less information is available about the material properties of biogenic calcite, despite its occurrence in a wide range of structures in different organisms. In particular, there is insufficient knowledge about h...

The majority of invertebrate skeletal tissues are composed of the most stable crystalline polymorphs of CaCO(3), calcite, and/or aragonite. Here we describe a composite skeletal tissue from an ascidian in which amorphous and crystalline calcium carbonate coexist in well-defined domains separated by an organic sheath. Each biogenic mineral phase has a characteristic Mg content (5.9 and 1.7 mol %...

Amorphous calcium carbonate (ACC) is a metastable phase often observed during low temperature inorganic synthesis and biomineralization. ACC transforms with aging or heating into a less hydrated form, and with time crystallizes to calcite or aragonite. The energetics of transformation and crystallization of synthetic and biogenic (extracted from California purple sea urchin larval spicules, Str...

Each of two calcitic stalagmites from Grotte de Clamouse, Herault, southern France, displays a discrete aragonite layer dated at around 1100 yr BP. The layer of fanning aragonite ray crystals is immediately preceded by calcite with Mg and Sr compositions that are uniquely high for the past 3 kyr. Trace element compositions close to the boundary between original aragonite and calcite are consist...

CaCO3 can crystallize as calcite, aragonite and vaterite. Calcite and aragonite are the most common biologically formed CaCO3 polymorphs, and vaterite is transformed into calcite via a solvent mediated process. Calcium carbonate makes an attractive model mineral for studies, since the morphology of CaCO3 has been the subject to control in biomineralization processes. And control of vaterite als...

Fluorite, barite and calcite are important industry minerals. However, they often co-exist, presenting difficulty in selectively separating them due to their similar surface properties. In this study, valonea extract and sodium fluosilicate were used as depressants to selectively separate them by flotation, with sodium oleate as the collector. The single mineral flotation results showed that va...

Dickinson and McGrath (2001, The Analyst 126, 1118–1121) used the ratio of integrated peak areas (not heights) of the calcite 104 and aragonite 221 peaks to develop a quantitative relationship for ratio of aragonite to calcite. That approach yields good quantitative results, if with the somewhat unsettling proviso that a 50-50 mixture of the two ploymorphs has a 104/221 intensity ratio much gre...

The role of soluble proteins from shell of the crayfish, Thenus Orientalis, was studied under different concentrations at an ambient temperature of 4°C in biomineralization. The composition and morphology of calcite and magnesium calcite crystals precipitated were investigated using Infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Figure 1. Crayfish ...

et al. (2) present a long, continuous, highresolution climate record extracted from a calcite vein in Devils Hole, Nevada. If their dating is accurate, the record appears to contradict the Milankovitch hypothesis (3). Dating of subsamples of the vein was done with the use of well-established principles of 230Th dating (4) and with recently developed techniques for precise measurement of 230Th a...

The thermophilic Geobacillus bacterium catalyzed the formation of 100-μm hexagonal crystals at 60°C in a hydrogel containing sodium acetate, calcium chloride, and magnesium sulfate. Under fluorescence microscopy, crystals fluoresced upon excitation at 365 ± 5, 480 ± 20, or 545 ± 15 nm. X-ray diffraction indicated that the crystals were magnesium-calcite in calcite-type calcium carbonate.