Changchengite
Changchengite is an IMA-recognized mineral species in the sulfosalt class, with the chemical formula IrBiS.
It crystallizes in the cubic crystal system (space group P2_13). It is a member of the Ullmannite structural group.
Key properties: Mohs hardness 3.7; specific gravity 11.96; Black streak; Metallic. R: (400) 41.3, (420) 45.2, (440) 45.5, (460) 46.0, (480) 46.4, (500) 46.6, (520) 46.9, (540) 47.1 luster.
IMA symbol Ccg, IMA status: approved, named in 1995.
Of hydrothermal origin in chromite bodies in dunites and placers derived therefrom.
It is found associated with Iridium, ferrian platinum, laurite, sperrylite, cooperite, irarsite, shuangfenite, mayingite, chromite, gold.
The name comes from the Chinese word for the Great Wall, situated nearby the occurrence.