A lot of black single crystal aggregates of the extremely rare selenium mineral stilleite from the famous deposit of Shinkolobwe (Shinkolobwe Mine, Shinkolobwe, Kambove, Haut-Katanga, DR Congo), that it is the type locality. Stilleite is the selenium analog of sphalerite. Ex Vandenbroucke Museum collection specimen, from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Stilleite
Zinc selenide — known only as microscopic gray inclusions inside linnaeite.
Intro adapted from Wikipedia (CC BY-SA).
Stilleite is an IMA-recognized mineral species in the sulfide class, with the chemical formula ZnSe.
It crystallizes in the cubic crystal system (space group F-43m). It is a member of the Sphalerite structural group.
Key properties: Mohs hardness 5; specific gravity 5.42.
IMA symbol Sll, grandfathered status — known before the IMA’s founding, named in 1956.
Included in linnaeite (Shinkolobwe, Congo); intermixed with other selenides (Santa Brigida mine, Argentina).
It is found associated with Pyrite, linnaeite, clausthalite, selenian vaesite, molybdenite, dolomite (Shinkolobwe, Congo); tiemannite, clausthalite, eucairite, umangite.
The mineral was named to honor Hans Stille (1876–1966), German geologist.