Structural Order of Mg-Stabilized Amorphous Calcium Carbonate and Its Associated Phase Transformation

28 January 2025, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Biominerals formed by marine organisms exhibit intricate structures and support a remarkable range of functionalities. Recent advances in our understanding of biomineralization highlight the pivotal role of magnesium-stabilized amorphous calcium carbonate (Mg-ACC) as a transient precursor in the formation of calcareous biominerals. This feature article summarizes recent in vitro studies of Mg-ACC, illustrating the concepts of particle attachment, secondary nucleation, domain segregation, and mesocrystal formation. Some conceptual issues associated with the ongoing debate between classical nucleation theory and non-classical nucleation theory are discussed. We suggest that solid-state NMR measurements of the van Vleck second moment provide a stringent test for any proposed atomic model of Mg-ACC. The coordination environment of Mg2+ ions and the significance of bicarbonate ions in Mg-ACC are discussed. The diffusion of Mg2+ ions within the calcitic lattice of high-Mg calcite offers a mechanistic insight into the 'dolomite problem'. The fusion of neighboring high-Mg calcite spherulites highlights their potential role as versatile building blocks for calcareous biomineral skeletal frameworks.

Keywords

Mg-Stabilized Amorphous Calcium Carbonate (Mg-ACC)

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