Apatite ball hand-ground from Madagascar 40mm.

Apatite is a mineral, or actually the name for a mineral group, because the composition of apatite can vary. The general chemical formula of the chlorine and fluorine-containing calcium phosphate is Ca5(PO4)3(F,Cl,OH). The apatite series is divided into: Fluorapatite: Ca5(PO4)3F Chlorapatite: Ca5(PO4)3Cl Hydroxyapatite: Ca5(PO4)3OH Complete mixing occurs between the chemical end members. Fluorapatite is by far the most common, which is why apatite is also used as a synonym for fluorapatite. Apatite can also contain a quantity of carbonate. Furthermore, it usually contains small quantities of certain metals, including iron, manganese, magnesium and uranium. Apatite is mainly formed in pegmatites, pneumatolites, under hydrothermal conditions and in alluvial deposits. The mineral is very common and occurs in Burma in the Mogok area (light blue, green or colourless specimens), sometimes with cat's eye effect. Similar apatites are found in Sri Lanka, these are blue and show cat's eye effect, others are green and yellow. Green stones with cat's eye effect are found in India. Beautiful red apatites have been discovered in Pakistan, in the Nasart area. Important occurrences of gemstone apatites are also known from Brazil, the stones are blue and green there, rarely light pink as in Morro Velho. Blue crystals up to 10 cm large occur in Urupuca, bluish fluorapatites come from Virgen da Plata and olive green from Campo Linda. In the USA apatites occur in Maine (violet-coloured crystals up to 25 cm in size; the stones cut from them weigh up to 170 ct). Animal bone tissue consists of 70% hydroxylapatite.