Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8910662 | Geochimica et Cosmochimica Acta | 2018 | 10 Pages |
Abstract
The incorporation of iodine into each of the three polymorphs of CaCO3 - calcite, aragonite and vaterite, is compared using first-principles computational simulation. In each case iodine is most easily accommodated as iodate (IO3â) onto the carbonate site. Local strain fields around the iodate solute atom are revealed in the pair distribution functions for the relaxed structures, which indicate that aragonite displays the greatest degree of local structural distortion while vaterite is relatively unaffected. The energy penalty for iodate incorporation is least significant in vaterite, and greatest in aragonite, with the implication that iodine will display significant partitioning between calcium carbonate polymorphs in the order vateriteâ¯>â¯calciteâ¯>â¯aragonite. Furthermore, we find that trace iodine incorporation into vaterite confers improved mechanical strength to vaterite crystals. Our results support the supposition that iodine is incorporated as iodate within biogenic carbonates, important in the application of I/Ca data in palaeoproxy studies of ocean oxygenation. Our observation that iodate is most easily accommodated into vaterite implies that the presence of vaterite in any biocalcification process, be it as an end-product or a precursor, should be taken into account when applying the I/Ca geochemical proxy.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geochemistry and Petrology
Authors
Xiaolei Feng, Simon A.T. Redfern,