The Apatite reference article from the English Wikipedia on 24-Jul-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Apatite

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).

Mohs hardness is 5. Refractive index is 1.632-1.646. Specific gravity is 3.17-3.23. Birefringence is .002-.004. Crystal structure is hexagonal.

Apatite is one of very few minerals which are produced and used by biological systems. Hydroxylapatite 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.

See also: list of minerals, thermal history modelling.

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