apatite

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Common calcium phosphate mineral, Ca₅(PO₄)₃(F,OH,Cl). Apatite has a hexagonal structure and occurs widely in igneous rocks, such as pegmatite, and in contact metamorphic rocks, such as marbles. It is used in the manufacture of fertilizer and as a source of phosphorus. Carbonate hydroxylapatite, Ca₅(PO₄,CO₃)₃(OH)₂, is the chief constituent of tooth enamel and, together with other related phosphate minerals, is the inorganic constituent of bone. Apatite ranks 5 on the Mohs scale of hardness.

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