Stable amorphous calcium carbonate is the main component of the calcium storage structures of the crustacean Orchestia cavimana

Amorphous calcium carbonate (ACC) is the least stable form of the six known phases of calcium carbonate. It is, however, produced and stabilized by a variety of organisms. In this study we examined calcium storage structures from the terrestrial crustacean Orchestia cavimana, in order to better understand their formation mode and function. By using X-ray diffraction, infrared and Raman spectroscopy, thermal analysis and elemental analysis, we determined that the mineral comprising these storage structures is amorphous calcium carbonate with small amounts of amorphous calcium phosphate (5%). We suggest that the use of amorphous calcium carbonate might be advantageous for these storage structures, which function as reservoirs of ions during the animal molting period. Its high solubility is beneficial for temporary storage of calcium carbonate ions that are subsequently dissolved and used elsewhere. Stabilization of these amorphous minerals is probably due to macromolecular constituents of the organic matrix, and to the magnesium and phosphate present in the mineral phase.