Brushite

Brushite

Possible Brushite crystals (not confirmed) found in bat guano in Jamaica
General
Category Phosphate mineral
Formula
(repeating unit)
CaHPO4·2H2O
Strunz classification 08.CJ.50
Crystal symmetry Monoclinic prismatic
H-M symbol: (2/m)
Space group: I2/a
Unit cell a = 6.265 Å, b = 15.19 Å, c = 5.814 Å; β = 116.47°; Z=4
Identification
Color Colorless to pale or ivory-yellow
Crystal habit Prismatic to tabular acicular crystals; typically powdery or earthy
Crystal system Monoclinic
Cleavage Perfect on {010} and {001}
Tenacity Brittle
Mohs scale hardness 2.5
Luster Vitreous, pearly on cleavages
Diaphaneity Transparent to translucent
Specific gravity 2.328
Optical properties Biaxial (+)
Refractive index nα = 1.539 - 1.540 nβ = 1.544 - 1.546 nγ = 1.551 - 1.552
Birefringence δ = 0.012
2V angle Measured: 59 to 87°
Solubility Readily in HCl
Other characteristics Piezoelectric
References [1][2][3]

Brushite is a phosphate mineral with the chemical formula CaHPO4·2H2O. It forms colorless to pale yellow monoclinic prismatic crystals and as powdery or earthy masses.[1][3] It is the phosphate analogue of the arsenate pharmacolite and the sulfate gypsum.

Discovery and occurrence

Brushite was first described in 1865 for an occurrence on Aves Island, Nueva Esparta, Venezuela, and named for the American mineralogist George Jarvis Brush (1831–1912).[2] It is believed to be a precursor of apatite and is found in guano-rich caves, formed by the interaction of guano with calcite and clay at a low pH. It occurs in phosphorite deposits and forms encrustations on old bones. It may result from runoff of fields which have received heavy fertilizer applications.[2] Associated minerals include tanarakite, ardealite, hydroxylapatite, variscite and gypsum.[1]

Brushite is the original precipitating material in calcium phosphate kidney stones.

References

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