Canfieldite
A rare silver-tin sulfide that commonly swaps in germanium for tin and tellurium for sulfur.
Intro adapted from Wikipedia (CC BY-SA).
Canfieldite is an IMA-recognized mineral species in the sulfide class, with the chemical formula Ag₈SnS₆.
It crystallizes in the cubic crystal system (space group F-43m). It is a member of the Argyrodite structural group.
Key properties: Mohs hardness 2.5; specific gravity 6.2–6.3; Gray-black, somewhat shining streak; Metallic. R: (400) 33.0, (420) 30.8, (440) 28.9, (460) 28.0, (480) 27.2, (500) 26.5, (520) 25.9, (540) 25.5 luster.
IMA symbol Cfi, grandfathered status — known before the IMA’s founding, named in 1894.
Found in polymetallic veins, formed very late in the paragenetic sequence.
It is found associated with Argyrodite, pyrargyrite, stephanite, acanthite, polybasite, freibergite, stannite, stannoidite, cassiterite, arsenopyrite, jordanite, marcasite, pyrrhotite.
The mineral was named to honor Frederick Alexander Canfield (1849–1926), American mining engineer and mineral collector of Dover, New Jersey, USA.