ABSTRACT
Apatite in the natural world comprises a major group of minerals which occurs in all geological environments. All the minerals of the group are hexagonal or monoclinic and based on a crystal structure which is hexagonal, a = 9.368Å, c = 6.844Å. Crystal chemical substitutions lead to a large variety of species in the group. Six species of calcium phosphate apatites are recognized.
Apatites occur in all geological environments usually as accessory minerals (<5%), but concentrations sufficient for economic interest other than gemstones are formed as sedimentary rocks and rarely as igneous segregations. Phosphate-rich deposits are exploited primarily for fertilizer. Museum quality specimens of fluorapatite are primarily from pegmatites, but unusually large crystals are found in skarn.
The closest apatite to bone apatite, carbonate- hydroxylapatite, is formed in very restricted environments usually by replacement of pre-existing organic matter or in guano deposits.
