The apatite group comprises three minerals:
Fluorapatite: Ca5(PO4)3F
Hydroxylapatite: Ca5(PO4)3(OH)
Chlorapatite: Ca5(PO4)3Cl
All of these are anhydrous phosphates containing hydroxyl or halogen
Fluorapatite is the commonest mineral in the apatite group.
Properties of fluorapatite:
Specific gravity: 3.1 to 3.25
Hardness: 5
Streak: White
Colour: Colourless, yellow, green, blue and purple. Manganoan varieties are dark green and blue-green.
Solubility: Apatite is slightly soluble in sulphuric acid and moderately soluble in hydrochloric and nitric acid

Plutonic igneous environments
Sedimentary environments
Metamorphic environments
Hydrothermal environments

Apatite is a primary and secondary mineral, widely distributed with important concentrations in carbonatites. It is the most common rock-forming phosphate and a major mineral in lithified phosphate-rich sediments. It occurs the oxidation zone of hypothermal (high temperature) veins and in Alpine cleft-type veins.
It is a common secondary mineral in high-temperature alteration zones (AofA).
Apatite is a common constituent of marble, skarn and magnetite deposits.
Apatite may also be found in quartzolite, granite, syenite, diorite, rhyolite, trachyte, andesite and basalt.

In the pegmatite at the Sapo mine, Minas Gerais, Brazil, apatite crystals are zoned, with a core of fluorapatite and an outer overgrowth of hydroxylapatite. They are associated with microcline, albite variety cleavelandite, quartz and muscovite (Min Rec 40.4.279-288).

At the Yates Prospect, Otter Lake, Quebec, Canada, it appears that fluorapatite is a primary mineral that crystallised from a carbonate melt (R&M 94.3.274-275).

Common impurities: OH,Cl,transition elements,La,Ce,Pr,Nd,Sm,Eu,Gd,Dy,Y,Er,Mn

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