Fluorapatite

Fluorapatite, often with the alternate spelling of fluoroapatite, is a mineral with the formula Ca₅(PO₄)₃F (calcium fluorophosphate). Fluorapatite 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. Fluorapatite crystallizes in a hexagonal crystal system. It is often combined as a solid solution with hydroxylapatite (Ca₅(PO₄)₃OH) in biological matrices. Chlorapatite (Ca₅(PO₄)₃Cl) is another related structure. Industrially, the mineral is an important source of both phosphoric and hydrofluoric acids.