1. Generic name for a class of minerals with compositions that are variants of the formula D5T3M, where D is a divalent cation, T is a trivalent tetrahedral compound ion, and M is a monovalent anion; calcium phosphate apatite’s are important mineral constituents of bones and teeth. See: hydroxyapatite.
2. Ca5(PO4)3(OH,F,Cl).