CONTROL OF ARAGONITE OR CALCITE POLYMORPHISM BY MOLLUSK SHELL MACROMOLECULES

Many mineralizing organisms selectively form either calcite or aragoni te, two polymorphs of calcium carbonate with very similar crystalline structures. Understanding how these organisms achieve this control has represented a major challenge in the field of biomineralization. Macr omolecules extracted from the aragonitic shell layers of some mollusks induced aragonite formation in vitro when preadsorbed on a substrate of beta-chitin and silk fibroin. Macromolecules from calcitic shell la yers induced mainly calcite formation under the same conditions, The r esults suggest that these macromolecules are responsible for the preci pitation of either aragonite or calcite in vivo.