Hydroboracite

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Hydroboracite
Hydroboracite.jpg
Hydroboracite, California(?)
General
Category Inoborates
Formula
(repeating unit)
CaMgB6O8(OH)6·3H2O
Strunz classification 6.CB.15
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group P2/c
Unit cell a = 11.76, b = 6.68
c = 8.23 [Å]; β = 102.59°; Z = 2
Identification
Colour Colourless, white
Mohs scale hardness 2
Luster Vitreous, silky
Diaphaneity Transparent
Optical properties Biaxial (+)
Refractive index nα = 1.520 - 1.523 nβ = 1.534 - 1.535 nγ = 1.569 - 1.571
Birefringence δ = 0.049
2V angle Measured: 60° to 66°, calculated: 62° to 66°
Dispersion Relatively weak
Solubility Very poorly soluble in cold water. Partially dissolved by prolonged submersion in boiling water.

Hydroboracite is a hydrated borate mineral (hence the name) of calcium and magnesium, whose chemical composition is CaMgB6O8(OH)6·3H2O. It was discovered in 1834 in Atyrau Province, Kazakhstan. Hydroboracite is a minor borate ore mineral.

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