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Formula: (NH4)Al(SO4)2.12H2O
Hydrated sulphate, alum group
Crystal System: Isometric
Specific gravity: 1.645 measured, 1.641 calculated
Hardness: 1½ to 2
Streak: White
Colour: Colourless, white; colourless in transmitted light
Luminescence: Nonfluorescent under UV
Environments
Tschermigite is an uncommon secondary mineral in
lignite and brown coal deposits and bituminous
shales and on burning coal seams or waste heaps, also as efflorescences
around solfataras or geothermal gas vents and fumaroles. Associated minerals on
shales and coals include gypsum,
ammoniojarosite, epsomite,
rostite and alunogen
(HOM).
Localities
At the Huangbaici coal field, Wuda Coal mining area, Wuda District, Wuhai, Inner Mongolia, China, mineral assemblages
that include the sulphates millosevichite,
alunogen, anhydrite,
tschermigite, coquimbite,
voltaite and godovikovite, as
well as the halide salammoniac and an unidentified phase, have been found
as encrustations on quartzofeldspathic sand and
sandstone adjacent to coal-fire gas vents associated with underground
coal fires.
The tschermigite formed by the reaction of coal-fire gas with
quartzofeldspathic rock or by hydrothermal alteration of this rock and
crystallisation from an acid-rich aqueous solution
(AM 90.1729–1739).
The type locality is Cermniky, Březno, Chomutov District, Ústí nad Labem Region, Czech Republic.
At the Geysers, West Mayacmas Mining District, Sonoma county, California, USA, tschermigite is associated with
boussingaultite, mascagnite
and voltaite
(HOM).
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