Tschermigite Locality: Cermniky (Tschermig), Kadaň (Kaaden), Ústí Region, Bohemia (Böhmen; Boehmen), Czech Republic Colourless columnar massive Tschermigite from the TL at Tschermig (now Cermniky). With a typed Freiberg label. Specimen size 4x5cm. Specimen and photo Leon Hupperichs. — Photo: Leon Hupperichs · CC BY-SA 3.0
Tschermigite
Natural ammonium alum — a water-soluble mineral of burning coal seams and fumaroles.
Intro adapted from Wikipedia (CC BY-SA).
Tschermigite is an IMA-recognized mineral species in the sulfate class, with the chemical formula (NH₄)Al(SO₄)₂·12H₂O.
It crystallizes in the cubic crystal system (space group Pa3). It is a member of the Alum structural group.
Key properties: Mohs hardness 1.5; specific gravity 1.645; Vitreous, silky if fibrous luster; refractive index 1.458; optically isotropic.
IMA symbol Tmi, grandfathered status — known before the IMA’s founding, named in 1853.
Occurs as an uncommon secondary mineral in lignite and brown coal deposits and bituminous shales and on burning coal seams or waste heaps; as efflorescences around solfataras or geothermal gas vents and fumaroles.
It is found associated with Gypsum, ammoniojarosite, epsomite, rostite, alunogen (shales and coals); boussingaultite, mascagnite, voltaite (The Geysers, California, USA).
The name is derived from the locality near the former Tschermig, Czech Republic.