Aragonite is a polymorph of calcium carbonate (CaCO3) encountered mainly in deposits in Spain, Slovenia, the United States, and in sandy deposits on the ocean floor in the Bahamas. It’s found in mollusk shells, where its purpose is mainly structurall1 as lamellae and prismatic columns, cemented to protein matrixes. In mollusk shells, the mineral component and the protein matrix form a composite material (mineral + polymer) called nacre (mother of pearl).
Its presence in biomineralized structures is associated with geochemical composition changes in the oceans. The presence of free Ca2+ and Mg2+ and the relation between their molar concentrations defines the calcium carbonate polymorph (CaCO3) – calcite or aragonite – to be deposited on the seabed. Different geological eras intertwined aragonite and calcite seas, affected by numerous factors, like hydrothermal activities associated with the expansion of the ocean floor and glaciation2 . The cost of metabolics reflect the physical-chemical state of the environment, and thus the cost-benefit can vary as a function of the environmental history of the planet.
