Ca10PO46F2

Ca10(PO4)6F2, commonly known as fluorapatite, is a mineral in the apatite group with the formula Ca10(PO4)6F2. It consists of calcium phosphate with fluoride ions occupying structural channels. Fluorapatite is the fluoride-substituted analogue of hydroxyapatite (Ca10(PO4)6(OH)2) and forms an important part of biological and geological phosphate minerals. In biology, fluoride incorporation into hydroxyapatite can lead to fluorapatite formation in tooth enamel and bone, increasing resistance to acid dissolution.

Structure and properties: Fluorapatite crystallizes in a hexagonal apatite lattice. The phosphate groups (PO4) form a network linked by calcium-oxygen polyhedra. Two fluoride ions reside in channels along the c-axis, replacing hydroxyl groups found in hydroxyapatite. This substitution generally reduces solubility and enhances chemical stability in acidic environments, contributing to greater acid resistance in enamel.

Occurrence: Naturally, fluorapatite occurs as a phosphate mineral in igneous and sedimentary rocks and as a component of biological apatite in bone and tooth enamel. In environments with elevated fluoride, the apatite structure readily accommodates fluoride, forming fluorapatite crystals that can be a significant fluoride reservoir in the crust.

Synthesis and applications: Fluorapatite can be synthesized by precipitation from calcium, phosphate, and fluoride sources or by converting hydroxyapatite through fluoride ion exchange. It is used in dental materials and coatings, and as a biocompatible component in bone substitutes due to its similarity to natural mineral and its lower solubility relative to hydroxyapatite. Safety considerations center on controlled fluoride release to avoid overexposure.

See also: Apatite, Hydroxyapatite, Chlorapatite, Fluoride.