Fluorapatite
General
Category	Phosphate mineral
Chemical formula	Ca5(PO4)3F
Identification
Color	Sea-green, violet, purple, blue, pink, yellow, brown, white, colorless, may be zoned
Crystal habit	Massive to prismatic cyrstaliine
Crystal system	Hexagonal - dipyramidal
Twinning	Contact twins rare
Cleavage	Indistinct
Fracture	Brittle to conchoidal
Mohs scale hardness	5
Luster	Vitreous, resinous to dull
Streak	White
Diaphaneity	Transparent to Opaque
Specific gravity	3.1 to 3.2
Optical properties	Uniaxial (-)
Refractive index	nω = 1.631 - 1.650 nε = 1.633 - 1.646
Birefringence	δ = 0.002
Ultraviolet fluorescence	Fluorescent and phosphorescent.
References	[1][2][3]

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.^[4]

Fluorapatite crystallizes in a hexagonal crystal system. It is often combined as a solid solution with hydroxylapatite (Ca₅(PO₄)₃OH) in biological matrices. Chlorapatite (Ca₅(PO₄)₃Cl) is another related structure.^[4]

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.^[1]

[edit] Synthesis

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.^[5]

3 Ca²⁺ + 2 PO3−4 → Ca₃(PO₄)₂

3 Ca₃(PO₄)₂ + CaF₂ → 2 Ca₅(PO₄)₃F

[edit] Applications

Fluorapatite can be used as a precursor for the production of phosphorus. It can be reduced by carbon in the presence of quartz:

4 Ca₅(PO₄)₃F + 21 SiO₂ + 30 C → 20 CaSiO₃ + 30 CO + SiF₄ + 6 P₂

Upon cooling, white phosphorus (P₄) is generated:

2 P₂ → P₄

[edit] References