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Tschermigite

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Tschermigite
Tschermigite from Tschermig, Bohemia.
General
CategorySulfate mineral
Formula
(repeating unit)
NH4Al(SO4)2·12(H2O)
Strunz classification7.CC.20
Crystal systemIsometric
Crystal classDiploidal (m3)
H-M symbol: (2/m 3)
Space groupPa3m3
Unit cella = 12.215 Å; Z = 4
Identification
ColorColorless, white; colorless in transmitted light
Crystal habitOctahedral crystals; fibrous columnar; powdery
CleavagePerfect on {100}
FractureConchoidal
Mohs scale hardness1+12 - 2
LusterVitreous, silky
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity1.645
Optical propertiesIsotropic
Refractive index1.458
BirefringenceAnomalously birefringent
SolubilityDeliquescent
References[1][2][3]

Tschermigite is a mineral form of ammonium alum, formula NH4Al(SO4)2·12(H2O). It is found in burning coal seams, bituminous shale and fumaroles. Because of its extreme water solubility it is unlikely to persist except in the dryest of conditions. Discovered in 1852 at Cermiky, also known as Tschermig in Bohemia. It is colorless and named for where it was discovered.

References