Influence of the Organic Matrix on Crystal Type in Molluscs

THE calcium carbonate of mollusc shells occurs as calcite in some species, as aragonite in others, and certain species deposit calcite in one portion of the shell and aragonite in another portion. Various explanations have been suggested for the formation of aragonite, which is significantly less stable. Participation of the enzyme carbonic anhydrase and the influence of the protein matrix on which the crystals are deposited have both been suggested 1 . We have investigated the capacity of pieces of decalcified matrix to induce aragonite formation when inserted into a mollusc which normally forms only calcite, and also under in vitro conditions in which calcium carbonate is normally precipitated as calcite.