Stilleite is a selenide mineral, zinc selenide, with the formula ZnSe. It has been found only as microscopic gray crystals occurring as inclusions in linnaeite associated with other selenide and sulfides. It was originally discovered in Katanga Province, Zaire in 1956 and is named for the German geologist, Hans Stille (1876–1966).^[4]

Stilleite
Single crystal aggregates of stilleite from the Shinkolobwe deposit
General
Category	Selenide mineral
Formula (repeating unit)	ZnSe
IMA symbol	Sll[1]
Strunz classification	2.CB.05a
Crystal system	Cubic
Crystal class	Hextetrahedral (43m) H-M symbol: (4 3m)
Space group	F43m
Unit cell	a = 5.667 Å; Z = 4
Structure
Jmol (3D)	Interactive image
Identification
Color	Gray
Mohs scale hardness	5
Luster	Metallic
Diaphaneity	Opaque to translucent
Specific gravity	5.42
Optical properties	Isotropic
Refractive index	About 2.5
References	[2][3]

It has been reported from the Santa Brigida mine, La Rioja Province, Argentina and from Tilkerode (Abberode) in the Harz Mountains, Germany.^[2] Associated minerals include pyrite, linnaeite, clausthalite, selenian vaesite, molybdenite and dolomite in the Shinkolobwe region of the Congo); and with tiemannite, clausthalite, eucairite, umangite, klockmannite in the Santa Brigida mine, Argentina.^[2]