Chrysothallite
A rare potassium-copper-thallium chloride — only the second known mineral with essential trivalent thallium, after avicennite.
Intro adapted from Wikipedia (CC BY-SA).
Chrysothallite is an IMA-recognized mineral species in the halide class, with the chemical formula K₆Cu₆Tl³⁺Cl₁₇(OH)₄·H₂O.
It crystallizes in the tetragonal crystal system (space group I4/mmm).
Key properties: Mohs hardness 3; specific gravity 2.95; Yellow streak; Vitreous luster; optically uniaxial.
IMA symbol Cry, IMA status: approved, named in 2013.
Formed by the interactions among high-temperature sublimate minerals, fumarolic gas and atmospheric water vapor at temperatures not higher than 150 flC.
It is found associated with Belloite, avdoninite, chlorothionite, sanguite, eriochalcite, mitscherlichite, sylvite, carnallite, kainite (Glavnaya Tenoritovaya fumarole); belloite.
The name refers to its bright golden-yellow color (from the Greek χρυσόϛ for gold) and the presence of thallium as a species-defining constituent.