Resolving a controversy of vaterite calcium carbonate, its structure, orientational order-disordering….

One of my articles is highlighted on the website of Mineralogical Society of America:
http://www.minsocam.org/pr20.html

Vaterite calcium carbonate is an important precursor in a number of carbonate-forming processes. Although it is a rare mineral in geological settings because of its meta-stability, it occurs in many biological settings. For a long time, the vaterite crystal structure has been controversial, especially on the CO3 ion orientation and ordering.

Wang et al.* discuss their first principles calculations and molecular dynamics simulations of vaterite. The results demonstrate that the previously accepted structure with fully disordered CO3 ions is only metastable, and a more stable superstructure with fully ordered carbonate ions is found. This ordered structure can be used to best describe CO3 orientational ordering in the structure and to explain some of experimentally observed properties of vaterite such as the changes in enthalpy during the transformation to calcite, and the negative volume change by heat treatment. Introducing the superstructure can be beneficial for atomic-scale descriptions of vaterite, since partial occupancy is difficult to implement explicitly in molecular models. Biomolecules, such as aspartic acid, can change the stability of vaterite. It remains to be seen, the interplay among the order-disorder transitions of the CO3 ions, biomolecules, and the stability of vaterite at biological interfaces. Answering these questions would provide fundamental understanding of the stability, properties, and functionalities of biogenic vaterite.

*Source:
American Mineralogist, Volume 94, pages 380–386, 2009

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