apatites

Apatites are a group of phosphate minerals with the general formula Ca5(PO4)3X, where X represents a halogen or hydroxyl group (F, Cl, or OH). The most common end-members are fluorapatite Ca5(PO4)3F, chlorapatite Ca5(PO4)3Cl, and hydroxyapatite Ca5(PO4)3(OH). They share a similar crystal structure and typically form hexagonal crystals that range from prismatic to tabular in habit. Color is variable, often colorless or white, with impurities producing pink, yellow, green, or brown hues.

Apatite is widespread in the Earth's crust and occurs as an accessory mineral in igneous and metamorphic rocks, and as the dominant phosphate phase in sedimentary phosphorite deposits. It forms in diverse environments, from magmatic crystallization to biomineralization, where hydroxyapatite is the mineral component of bone and tooth enamel in vertebrates.

Economic importance centers on phosphorus supply. The apatite group constitutes the principal source of phosphorus for fertilizers; phosphate rock containing apatite is processed to produce phosphoric acid and various phosphate-based fertilizers. In addition to its industrial role, apatite can occur as a gemstone, particularly blue varieties, though it is less common in jewelry due to its relative softness and occurrence.

Name and etymology trace to the Greek apate, meaning deception, reflecting historical confusion with similar-looking minerals. The term apatite therefore denotes a mineral group rather than a single pure compound, highlighting both its compositional variability and its pervasive presence in geological and biological systems.