Mg K-edge XAFS analysis of biogenic aragonite

Abstract We determined the local structure of magnesium in biogenic aragonite using X-ray absorption fine-structure spectroscopy. Using adequate standard material, it was revealed for the first time that the local structure of magnesium in biogenic aragonite is identical to that in synthesized aragonite. The incorporated magnesium is six-fold coordinated and does not isomorphously substitute for the nine-fold calcium ion in aragonite. This suggests that magnesium either adopts a distorted coordination in the aragonite or is incorporated into an amorphous calcium carbonate.