Calcite, Aragonite and Vaterite


The three stable modifications of calcium carbonate (calcite, aragonite und vaterite) have different biological roles, which can be derived in part from their different structures.

Although vaterite, the modification with the lowest thermodynamic stability, only plays a secondary role as a structural matrix for a few marine animals (gastropodes, i.e. snails) and for the storage of calcium in leaves, many different roles are known for calcite and aragonite.

Calcite (hexagonal)

Aragonite (orthorhombic)

Known functions:
  • Exoskeleton in coccolithophores,
    foraminopheres, molluscs
  • crabs' claws
  • egg shells
Known functions:
  • Exoskeleton in clam shells
  • Gravitation receptors

Often, both CaCO3 modifications are found together. One example for the functional cooperation of calcite and aragonite is the composition of clam shells. Here, organic components play a decisive role along with the inorganic components.