Phase transformation-induced Mg isotope fractionation in Mg-mediated CaCO3 mineralization

The biomineralization of CaCO3 often involves the transformation of amorphous precursors into crystalline phases, which is regulated by various proteins and inorganic ions such as Mg2+ ions. While the effects of Mg2+ ions on the polymorph and shape of the crystalline CaCO3 have been observed and studied, the interplay between Mg2+ ions and CaCO3 during the mineralization remains unclear. This work focuses on the mechanism of Mg2+ ion-regulated mineralization of CaCO3. By tracing the Mg isotope fractionation, the different mineralization pathways of CaCO3 under different Mg2+ ion concentrations had been clarified. Detailed regulatory role of Mg2+ ions at the different stages of mineralization had been proposed through combining the fractionation data with the analyses of the CaCO3 polymorph and shape evolution. These results provide a clear view of the Mg-mediated crystallization process of amorphous CaCO3, which can be used to finely control the phase of the crystalline products according to different needs.