Brushite

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Brushite
Bat Guano 2.tif
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]

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.

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).[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[edit]

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