apatite A widely distributed phosphate mineral, with the formula Ca₅(PO₄)₃(F,Cl,OH); sp. gr. 3.1–3.3; hardness 5; hexagonal; usually a shade of green or grey-green, but may also be white, brown, yellow, bluish, or red; white streak; vitreous lustre; crystals commonly hexagonal prisms, and often tabular, also occurs massive, and granular; cleavage, basal {0001}, imperfect prismatic {1010}; found as an accessory mineral in igneous rock, in pegmatites and high-temperature hydrothermal veins, and in metamorphic rocks. It is the principal constituent of fossil bones (see also COLLOPHANE). Apatite is widely used as a phosphate fertilizer, and for the production of phosphoric acid and various other chemicals.

apatite A complex mineral form of the salt calcium phosphate, Ca₅(PO₄)₃(OH,F,Cl), that is the main constituent of the enamel of teeth.