Fluorapatite

Infobox mineral
name = Fluorapatite
category = Phosphate mineral
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formula = Ca₅(PO₄)₃F
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color = Sea-green, violet, purple, blue, pink, yellow, brown, white, colorless, may be zoned
habit = Massive to prismatic cyrstaliine
system = Hexagonal - dipyramidal
twinning = Contact twins rare
cleavage = Indistinct
fracture = Brittle to conchoidal
tenacity =
mohs = 5
luster = Vitreous, resinous to dull
polish =
refractive = nω = 1.631 - 1.650 nε = 1.633 - 1.646
opticalprop = Uniaxial (-)
birefringence = δ = 0.002
dispersion =
pleochroism =
fluorescence= Fluorescent and phosphorescent.
absorption =
streak = White
gravity = 3.1 to 3.2
density =
melt =
fusibility =
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solubility =
diaphaneity = Transparent to Opaque
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references =http://rruff.geo.arizona.edu/doclib/hom/fluorapatite.pdf Mineral Handbook] [http://webmineral.com/data/Fluorapatite.shtml Webmineral] [http://www.mindat.org/min-1572.html Mindat]

Fluorapatite, often with the alternate spelling of fluoroapatite, is a mineral with the formula Ca₅(PO₄)₃F (calcium halophosphate). Fluorapatite is a hard crystalline solid. Although samples can have various color (green, brown, blue, violet, or colorless), the pure mineral is colorless as expected for a material lacking transition metals. It is an important constituent of tooth enamel.Hurlbert and Klein. "Manual of Mineralogy, 19th Edition". 1977. ISBN 0471251771]

Fluorapatite crystallizes in a hexagonal crystal system. It is often combined as a solid solution with hydroxylapatite (Ca₅(PO₄)₃OH) in biological matrices. Chloroapatite (Ca₅(PO₄)₃Cl) is another related structure.

Fluorapatite is the most common phosphate mineral. It occurs widely as an accessory mineral in igneous rocks and in calcium rich metamorphic rocks. It commonly occurs as a detrital or diagenic mineral in sedimentary rocks and is an essential component of phosphorite ore deposits. It occurs as a residual mineral in lateritic soils.

ynthesis

Fluorapatite can be synthesized in a two step process. First, calcium phosphate is generated by combining calcium and phosphate salts at neutral pH.This material then reacts further with fluoride sources (often sodium monofluorophosphate or calcium fluoride (CaF₂)) to give the mineral. This reaction is integral in the global phosphorus cycle. [Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.]

:3Ca²⁺ + 2PO₄^3- → Ca₃(PO₄)₂

:3 Ca₃(PO₄)₂ + CaF₂ → 2 Ca₅(PO₄)₃F

Fluorapatite can also be used as a precursor for the production of phosphorus. The mineral can be reduced by carbon in the presence of quartz, ultimately generating white phosphorus, P₄::Ca₅(PO₄)₃F + 3SiO₂ + 5C → 3CaSiO₃ + 5CO + P₂2P₂ → P₄ after cooling.

References