Crystal structure model of apatite, 1981.
© Science Museum / Science & Society Picture Library
A model built by built by Arnold Beevers. Apatite is a phosphate of calcium, which also contains fluoride, chloride, hydroxyl or carbonate ions, according to the variety. It is a major constituent of sedimentary phosphate rocks, of the bones and teeth of vertebrate animals, and it is usually present as an accesory mineral in igneous rocks.