common phosphate mineral, a calcium fluoride phosphate, Ca₅(PO₄)₃F. It occurs as minute, often green, glassy crystals in many igneous rocks, and also in magnetite deposits, high-temperature hydrothermal veins, and metamorphic rocks; it also occurs as collophane in marine deposits. For detailed physical properties, see phosphate mineral (table).

The fluoride ion is often replaced in the crystal structure by chloride or a hydroxide group; in nature there are complete chemical variations, called solid-solution (solid solution) series, between fluorapatite and chlorapatite and between fluorapatite and hydroxylapatite. Manganese can replace up to 10 percent of the calcium in fluorapatite derived from granite pegmatites.