Apatite

apatite

hydroxylapatite

fluorapatite

turquoise

Images

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.

Varieties

Collophane is a carbonate-rich variety of apatite

Properties

Specific gravity: 3.1 to 3.25
Hardness: 5
Streak: White
Colour: Colourless to white, grey, also green, blue, pink, yellow, brown, violet, purple, red
Common impurities: OH,Cl,transition elements,La,Ce,Pr,Nd,Sm,Eu,Gd,Dy,Y,Er,Mn
Environments

Plutonic igneous environments
Pegmatites
Carbonatites
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 hydrothermal alteration zones (AofA).

Apatite is a common constituent of marble, skarn and magnetite deposits.
It may also be found in quartzolite, granite, syenite, diorite, rhyolite, trachyte, andesite and basalt.

Apatite crystallises in the hexagonal system, point group 6/m. Crystals are common, tabular parallel to {0001} or short to long prismatic with {1010}, {1011} and minor {0001}, sometimes together with other prisms and bipyramids (OJ).

Localities

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 Nacozari, Mexico, turquoise pseudomorphs after apatite have been found (KL p211).

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