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Tschermigit (Ammonalaun) - Tschermig, Böhmen.jpg
Tschermigite from Tschermig, Bohemia.
Category Sulfate mineral
(repeating unit)
Strunz classification 7.CC.20
Crystal system Isometric
Crystal class Diploidal (m3)
H-M symbol: (2/m 3)
Space group Pa3m3
Unit cell a = 12.215 Å; Z = 4
Color Colorless, white; colorless in transmitted light
Crystal habit Octahedral crystals; fibrous columnar; powdery
Cleavage Perfect on {100}
Fracture Conchoidal
Mohs scale hardness 1½ - 2
Luster Vitreous, silky
Streak White
Diaphaneity Transparent to translucent
Specific gravity 1.645
Optical properties Isotropic
Refractive index 1.458
Birefringence Anomalously birefringent
Solubility Deliquescent
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.