Vaterite analysis

Secondary mineralization at Mount Keith produces hydromagnesite, while mineralization at Diavik includes carbonates of Mg, Ca and Na nesquehonite, calcite, vaterite, natrite, thermonatrite, natron, trona, gaylussite and northupite. The rate of carbon mineralization at the two mine sites was assessed using quantitative powder X-ray diffraction analysis and the Rietveld... 

This method of analysis is particularly valuable when chemical methods are inadequate or inapplicable. For instance, for complex mixtures where the different elements or ions may be associated in many different ways, all compatible with the analytical figures or for mixtures of polymorphous forms of the same substance, such as the three crystalline forms of CaC03 (calcite, aragonite, and vaterite) or the three crystalline forms of FeO(OH) (goethite, lepidocrocite, and P FeO(OH)—see Bunn, 1941)—mixtures for which chemical analytical methods are irrelevant. 

On a relative basis, i.e. residues per 1000, there is virtually no one species like the other. In contrast, different shell samples from the same species and obtained from the same natural habitat yield identical amino acid patterns. It is of interest that (1) the structure of carbonates (aragonite-calcite-vaterite), (2) the content in trace elements, and (3) the stable isotope distribution are markedly effected by fluctuations in salinity, water temperature, Eh/pH conditions, and some anthropogenic factors. The same environmental parameters determine to a certain degree the chemical composition of the shell organic matrix. This feature suggests a cause-effect relationship between mineralogy and organic chemistry of a shell. In the final analysis, however, it is simply a reflection of the environmentally-controlled dynamics of the cell. 

XRD analysis has revealed the presence of several different types of carbonate minerals in liquefaction residues from a number of coals. Minerals identified included vaterite and calcite (two polymorphs of CaCO,) dolomite (CaMg[C03]2) and in the residue from a high sulfur coal (2.26 db), anhydrite (CaSO,) was identified. The types of mineral deposits formed depend not only on the coal but also on the reaction conditions. Our data indicates that whilst vaterite forms at low temperatures (380°C), as the temperature increases, the vaterite becomes progressively converted to calcite, the more stable form. After further increases in temperature, particularly at long reaction times, dolomite begins to form. 

X-ray diffraction analysis of the films showed calcite, vaterite, and a broad amorphous region due to the organic material and/or amorphous calcium carbonate. 

Much more attention was paid to the transformation process of vaterite to calcite. Upon heating at 730 K, vaterite irreversibly transforms into calcite. This transformation in aqueous solution at ambient conditions was a solution-mediated process [42]. All of the experimental results and the data analysis indicated that the transformation took place through dissolution of vaterite, followed by the crystallization of calcite. 

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