Fluoroapatite

Fluoroapatite, often with the alternate spelling of fluorapatite, is a mineral with the formula Ca5(PO4)3F (calcium halophosphate). Fluoroapatite is a hard crystalline solid. Although samples can have various color (green, brown, blue, violet, or colorless), the pure mineral is colorless as expected for a material lacking transition metals. It is an important constituent of tooth enamel.

Fluoroapatite crystallizes in a hexagonal crystal system. It is often combined as a solid solution with hydroxylapatite (Ca5(PO4)3OH) in biological matrices. Chloroapatite (Ca5(PO4)3Cl) is another related structure.

Fluoroapatite can be synthesized in a two step process. First, calcium phosphate is generated by combining calcium and phosphate salts at neutral pH.This material then reacts further with fluoride sources (often sodium monofluorophosphate or calcium fluoride (CaF2)) to give the mineral. This reaction is integral in the global phosphorus cycle.


 * 3Ca2+ + 2PO43- &rarr;  Ca3(PO4)2


 * 3 Ca3(PO4)2 + CaF2 &rarr;  2 Ca5(PO4)3F

Fluoroapatite can also be used as a precursor for the production of phosphorus. The mineral can be reduced by carbon in the presence of quartz, ultimately generating white phosphorus, P4:
 * Ca5(PO4)3F + 3SiO2 + 5C &rarr;  3CaSiO3 + 5CO + P2

2P2 →  P4 after cooling