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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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