Crystalline and Amorphous Precursors to Aragonite but Not Calcite Biomineral Formation

Analyzing 200 million spectra with Myriad Mapping (MM) of nanoscale mineral phases we found expected and unexpected precursors on the surface of forming coral skeleton and nacre, but not on sea urchin spines. The expected phases, found on all biominerals (1-11), were amorphous calcium carbonate hydrated (ACCH₂O) and anhydrous (ACC). The unexpected crystalline precursors were calcium carbonate hemihydrate (CaCO₃-½H₂O, CCHH) and monohydrocalcite (CaCO₃-1H₂O, MHC)(12). CCHH, in particular, had been synthesized I the lab (13) and fully characterized, but had never been observed as a natural mineral of biomineral. The observation of crystalline precursors demonstrates that biomineralization pathways are more complex and diverse than previously understood, opening new avenues for the synthesis of self-assembled materials via multiple metastable precursor phases, amorphous and crystalline.<br/><br/>1. E Beniash, . . . S Weiner 1997 DOI: https://doi.org/10.1098/rspb.1997.0066<br/>2. M Najman, . . . GD Stasio 2004<br/>3. Y Politi, . . . L Addadi 2004 DOI: 10.1126/science.110228<br/>4. Y Politi, . . . PUPA Gilbert 2008 DOI: https://doi.org/10.1073/pnas.0806604105<br/>5. YUT Gong, . . . PUPA Gilbert 2012 DOI: https://doi.org/10.1073/pnas.1118085109<br/>6. RT DeVol, . . . PUPA Gilbert 2015 DOI: https://doi.org/10.1021/jacs.5b07931<br/>7. MA Marcus, . . . PUPA Gilbert 2017 DOI: https://doi.org/10.1021/acsnano.7b05044<br/>8. T Mass, . . . PUPA Gilbert 2017 DOI: https://doi.org/10.1073/pnas.1707890114<br/>9. C-Y Sun, . . . PUPA Gilbert 2017 DOI: https://doi.org/10.1021/acsnano.7b00127<br/>10. C-Y Sun, . . . PUPA Gilbert 2020 DOI: https://doi.org/10.1073/pnas.2012025117<br/>11. CA Stifler, . . . PUPA Gilbert 2021 DOI: https://doi.org/10.1021/acs.cgd.1c00865<br/>12. CA Schmidt, . . . PUPA Gilbert 2024 DOI: https://doi.org/10.1038/s41467-024-46117-x<br/>13. Z Zou, . . . P Fratzl 2019 DOI: 10.1126/science.aav021