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Bat Guano 2.tif
Possible Brushite crystals (not confirmed) found in bat guano in Jamaica
Category Phosphate mineral
(repeating unit)
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
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[edit]

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.[citation needed]