Apatite is the chief phosphate mineral (calcium phosphate associated with fluoride, chloride, or hydroxyl ions), large deposits of which are found in the Kola peninsula, Russia, North Africa, and Montana and Florida. It is found in igneous rocks and sedimentary deposits. It is mined for fertilizer and is the major ore of phosphorus.
The chemical composition of apatite is Ca5(PO4)3X, where X = F (fluorapatite, the most common), Cl (chlorapatite), OH (hydroxyapatite), or a mixture of all three; it forms prismatic or tabular hexagonal crystals, and also occurs as granular aggregates or in massive crusts. It is usually too soft for cutting and polishing, though there are two gem varieties. Hardness 5, specific gravity 3.1–3.4.