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 the Inder lake, Atyrau Province, Kazakhstan. Hydroboracite is a minor borate ore mineral.

Hydroboracite
General
CategoryInoborates
Formula
(repeating unit)
CaMgB6O8(OH)6·3H2O
IMA symbolHbo[1]
Strunz classification6.CB.15
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP2/c
Unit cella = 11.76, b = 6.68
c = 8.23 [Å]; β = 102.59°; Z = 2
Identification
ColourColourless, white
Mohs scale hardness2
LusterVitreous, silky
DiaphaneityTransparent
Optical propertiesBiaxial (+)
Refractive indexnα = 1.520 – 1.523 nβ = 1.534 – 1.535 nγ = 1.569 – 1.571
Birefringenceδ = 0.049
2V angleMeasured: 60° to 66°, calculated: 62° to 66°
DispersionRelatively weak
SolubilityVery poorly soluble in cold water. Partially dissolved by prolonged submersion in boiling water.
References[2][3]

References

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  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Webmineral data
  3. ^ Mindat