Mg coordination in biogenic carbonates constrained by theoretical and experimental XANES

Toshihiro Yoshimura, Yusuke Tamenori, Osamu Takahashi, Luan T. Nguyen, Hiroshi Hasegawa, Nozomu Iwasaki, Azumi Kuroyanagi, Atsushi Suzuki, Hodaka Kawahata

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)


Incorporation of magnesium into biogenic calcium carbonate is widely used to infer the conditions of mineral growth. From a mineralogical perspective, the dominant chemical environment of Mg and whether Mg replaces calcium by ideal substitution in biogenic CaCO3 are still debated, however. Here we show that energy positions and resonance features in experimental and theoretical XANES spectra can be used to identify the dominant molecular host site. In all biogenic calcite, which is produced by foraminifera, corals, bivalves, and brachiopods, the local environment of Mg indicated that it is incorporated primarily as a structural substitute for calcium in the crystal lattice, but in aragonitic coral and bivalves a pronounced effect of the organic fraction or disordered phases was observed. These differences among CaCO3 polymorphs suggest that physicochemical parameters affect the final composition of biogenic calcite, but in aragonite-secreting organisms, there may be physiological controls on Mg concentrations in biogenic aragonite.

Original languageEnglish
Pages (from-to)68-74
Number of pages7
JournalEarth and Planetary Science Letters
Publication statusPublished - 2015 Jul 1


  • Aragonite
  • Calcite
  • Coordination
  • Magnesium


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