Fluorapatite, often with the alternate spelling of fluoroapatite, is a phosphate mineral with the formula Ca5(PO4)3F (calcium fluorophosphate). Fluorapatite is a hard crystalline solid. Although samples can have various color (green, brown, blue, yellow, violet, or colorless), the pure mineral is colorless, as expected for a material lacking transition metals. Along with hydroxylapatite, it can be a component of tooth enamel, but for industrial use both minerals are mined in the form of phosphate rock, whose usual mineral composition is primarily fluorapatite but often with significant amounts of the other.
Fluorapatite (pink) on top of muscovite (green)
Fluorapatite grains in carbonate groundmass. Photomicrographs of thin section from Siilinjärvi apatite ore.
Fluorapatite. São Geraldo do Baixio, Doce valley, Minas Gerais, Brazil.
Phosphate minerals contain the tetrahedrally coordinated phosphate (PO43−) anion, sometimes with arsenate (AsO43−) and vanadate (VO43−) substitutions, along with chloride (Cl−), fluoride (F−), and hydroxide (OH−) anions, that also fit into the crystal structure.
Apatite
Thin section of apatite-rich carbonate in cross polarized transmitted light.