apatit

Apatite is a group of phosphate minerals with a common structural framework and a general chemical formula of Ca5(PO4)3(X), where X represents fluorine (F), chlorine (Cl), or hydroxyl (OH). The mineral typically crystallizes in the hexagonal system and forms prismatic to tabular crystals in a range of colors, including colorless, green, blue, and brown. It is widely distributed in igneous, metamorphic, and sedimentary rocks and is also the primary source of phosphorus for fertilizers. In biology, hydroxyapatite is the mineral component of bone and tooth enamel.

Major varieties in the apatite group include fluorapatite Ca5(PO4)3F, chlorapatite Ca5(PO4)3Cl, and hydroxyapatite Ca5(PO4)3(OH). The minerals are often transparent to translucent, and some specimens display fluorescence under ultraviolet light. Although relatively soft compared with many gemstones, apatite can be cut into cabochons or facets for collector pieces, particularly for rare blue and green crystals. Its Mohs hardness is about 5.

Geologically, apatite forms in a variety of settings. It is common in phosphorus-rich igneous rocks such as carbonatites and granitic pegmatites, and it occurs in sedimentary rocks as phosphorite nodules. It also appears in hydrothermal veins and as an accessory mineral in many rock types, frequently associated with fluorite, zircon, and other phosphate minerals.

The name apatite is traditionally thought to derive from Greek apatas, meaning deception or mislead, reflecting how the mineral can be mistaken for other minerals in hand specimens. Economically, its most significant role is as a source of phosphorus for fertilizers, underpinning global agricultural productivity.