[B-PT03] Biocalcification and the Geochemistry of Proxies -Field ecology, Laboratory culture and Paleo

[BPT03-14] Inorganic precipitation mechanism of calcium carbonate polymorphs and their precursors

*Jun KAWANO¹ (1.Creative Research Institution, Hokkaido University)

Calcium carbonate, CaCO₃, occurs in six different forms: three crystalline polymorphs (calcite, aragonite, and vaterite), two hydrate phases, and amorphous calcium carbonate (ACC). These polymorphs are important both in life and material sciences, especially the occurrence of CaCO₃ in living organisms has received considerable attention. As a basis for understanding biomineralization, inorganic precipitation mechamism of these polymorphs has been extensively investigated for over a hundred years. Recently, crystallization pathway through non-classical mechanism such as stable prenucletaion cluster aggregation has been proposed, which give a new picture of the early stages of calcium carbonate growth. However our knowledge of formation process of CaCO₃, especially that of the mechanism of polymorph selection, is far from complete.
We have investigated experimentally and theoretically the metastable formation of CaCO₃ polymorphs and their precursors. In particular, the effect of Mg²⁺ on the nucleation and growth of CaCO₃ polymorphs has been focused and the quantum chemical calculations of Mg-containing CaCO₃ surfaces and clusters appearing in the early stages of CaCO₃ formation have been performed. As a result, Mg²⁺ substituted for Ca²⁺ affects the structure of surfaces and clusters, and may have significant effect on the polymorph selection of CaCO₃. In this presentation, we will report our results in detail based on the recent progress in this field.