Brushite

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.[2][4] It is the phosphate analogue of the arsenate pharmacolite and the sulfate gypsum.

Brushite
Possible Brushite crystals (not confirmed) found in bat guano in Jamaica
General
CategoryPhosphate mineral
Formula
(repeating unit)		CaHPO4·2H2O
Strunz classification8.CJ.50
Crystal systemMonoclinic
Crystal classDomatic (m)
(same H-M symbol)
Space groupAa
Unit cella = 6.265 Å, b = 15.19 Å,
c = 5.814 Å; β = 116.47°; Z = 4
Identification
ColorColorless to pale or ivory-yellow
Crystal habitPrismatic to tabular acicular crystals; typically powdery or earthy
CleavagePerfect on {010} and {001}
TenacityBrittle
Mohs scale hardness2.5
LusterVitreous, pearly on cleavages
DiaphaneityTransparent to translucent
Specific gravity2.328
Optical propertiesBiaxial (+)
Refractive indexnα = 1.539 - 1.540 nβ = 1.544 - 1.546 nγ = 1.551 - 1.552
Birefringenceδ = 0.012
2V angleMeasured: 59 to 87°
SolubilityReadily in HCl
Other characteristicsPiezoelectric
References[1][2][3][4]

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).[3] 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.[3] Associated minerals include tanarakite, ardealite, hydroxylapatite, variscite and gypsum.[2]

Brushite is the original precipitating material in calcium phosphate kidney stones.[5] It is also one of the minerals present in dental calculi.

References
  1. Mineralienatlas
  2. Brushite in the Handbook of Mineralogy
  3. Brushite on Mindat.org
  4. Webmineral data
  5. "Brushite". Virtual Museum of Molecules and Minerals. Retrieved 22 December 2017.
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