APATITE STRUCTURES

Apatites have the formula, Ca10(PO4)6X2, with X commonly OH, F or Cl. The apatite lattice is very tolerant of substitutions and vacancies, for example Ca can be replaced by Sr, Pb and Na, and PO4 by AsO4 and VO4. Apatites are widely distributed as accessory minerals in igneous rocks and in small quantities in most metamorphic rocks. Rock phosphates (microcrystalline apatite) of biological origin are the starting material for phosphate fertilizer manufacture; synthetic apatites are used as phosphors in fluorescent light tubes; and impure microcrystalline hydroxyapatite (HAP) forms the mineral (bioapatite) of bones and teeth.