Fluorine incorporation into calcite, aragonite and vaterite CaCO3: Computational chemistry insights and geochemistry implications
| Autor: | Zvi Steiner, Simon A. T. Redfern, Xiaolei Feng |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2021 |
| Předmět: |
Calcite
010504 meteorology & atmospheric sciences Aragonite Inorganic chemistry chemistry.chemical_element engineering.material Calcium 010502 geochemistry & geophysics 01 natural sciences Ion chemistry.chemical_compound Calcium carbonate chemistry Geochemistry and Petrology Vaterite engineering Fluorine Carbonate 14. Life underwater 0105 earth and related environmental sciences |
| Popis: | The abundant occurrence of calcium carbonate minerals in marine sediments and their high fluorine content suggests that fluorine is a good candidate for reconstructing paleoceanographic parameters. However, the potential of fluorine as a paleoproxy had hardly been explored, and fundamental insights into the behaviour of fluorine in biogenic carbonates and marine sediments is required. A first-principles modelling approach is used here to analyse the incorporation mechanisms of fluorine into crystalline calcium carbonates. We compute F incorporation into the CaCO3 lattice via a number of mechanisms, but concentrate on comparison of the energetics of the two easiest substitution mechanisms: replacing one oxygen atom within the carbonate group to form a (CO2F)− group as against a substitution involving replacement of the CO3 group by two fluorine ions to form a CaF2 defect. These incorporation mechanisms are fundamentally different from that of iodine into calcium carbonates, where a carbon atom is replaced. Our simulations suggest that the substitution of CO 3 2 - by F 2 2 - is the most favoured and that fluorine is preferentially incorporated into the three naturally-occurring polymorphs of calcium carbonate in the order vaterite ⪆ aragonite ≫ calcite. These results explain the previously-reported preponderance of fluorine in aragonite corals, and lend support to the use of F/Ca as a proxy for ocean pCO2. |
| Databáze: | OpenAIRE |
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