Apatite is a group of minerals, usually referring to: hydroxylapatite , fluorapatite, and chlorapatite, named for high concentrations of OH-, F-, or Cl- ions, respectively, in the crystal lattice. The formula of the admixture of the three most common species is Ca5(PO4)3(OH, F, Cl).
Apatite is one of very few minerals which are produced and used by biological systems. Hydroxyapatite is the major component of tooth enamel, and a large component of bone material. Fluorapatite is slightly stronger than hydroxyapatite; thus, fluoridated water, which will allow exchange in the teeth of hydroxyl ions for fluoride ions, slightly strengthens the teeth.
Fission tracks in apatite are commonly used to estimate the thermal history of sediments in sedimentary basins.
Phosphorite is the name given to impure, massive apatite.