Steel grey crystal aggregates of the very rare mineral Cu-Ni sulphide mineral fletcherite from the type locality in Fletcher mine (Fletcher Mine, West Fork, Reynolds County, Missouri, United States of America). Ex Vandenbroucke Museum collection from Waregem, Belgium — Photo: David Hospital · CC BY 4.0
Fletcherite
A rare steel-gray copper-nickel-cobalt thiospinel of the linnaeite group.
Intro adapted from Wikipedia (CC BY-SA).
Fletcherite is an IMA-recognized mineral species in the sulfide class, with the chemical formula CuNi₂S₄.
It crystallizes in the cubic crystal system (space group Fd3m). It is a member of the Spinel structural group.
Key properties: specific gravity 4.76; Metallic. R: (420) 36.4, (460) 40.9, (500) 42.5, (546) 43.4, (589) 45.3, (640) 43.8 luster.
IMA symbol Ftc, IMA status: approved, named in 1976.
Disseminated in copper sulfides, in copper-rich pods replacing dolostone (Fletcher mine, Missouri, USA); in black slates (Kalgoorlie, Australia).
It is found associated with Vaesite, pyrite, covellite, chalcopyrite, bornite, digenite (Fletcher mine, Missouri, USA); pyrrhotite (Kalgoorlie, Australia).
The name refers to the Fletcher mine in Missouri, USA.