Stangersite
Stangersite is an IMA-recognized mineral species in the sulfide class, with the chemical formula SnGeS₃.
It crystallizes in the monoclinic crystal system (space group P2_1/c).
Key properties: Mohs hardness 2; specific gravity 3.98; Very light yellowish brown streak; Vitreous to adamantine luster.
IMA symbol Sgs, IMA status: approved, named in 2020.
On rock fragments and on crumbly black ash in the central part of a spontaneously burning coal mine dump. Formed under reducing conditions by direct crystallization from hot gasses (250-350 flC) containing Cl and F.
It is found associated with Greenockite, herzenbergite, unnamed GeS2 and GeAsS (crystals); members of Bi-Sb, Bi2S3-Sb2S3 and Bi2S3-Bi2Se3 solid solutions, Bi3S2.
The name refers to the essential chemical elements: Sn (stannum), Ge (germanium) and S (sulphur).