Outstanding grey crystals of the very rare mineral duranusite from the type locality (L'Eguisse Mine, Duranus, Provence-Alpes-Cote d'Azur, France), associated to realgar. Duranusite is a arsenic sulphide of rare composition As4S. — Photo: David Hospital · CC BY-SA 4.0
Duranusite
Duranusite is an IMA-recognized mineral species in the sulfide class, with the chemical formula As₄S.
It crystallizes in the orthorhombic crystal system.
Key properties: specific gravity 4.5; Metallic. R1 –R2: (400) 39.0–42.0, (420) 36.8–39.4, (440) 34.6–36.8, (460) 33.0–34.8, (480) 32.1–33.6, (500) 31.4–32.7 luster.
IMA symbol Du, IMA status: approved, named in 1973.
Found in calcite veinlets in marls and siliceous limestones (Duranus, France).
It is found associated with Arsenic, realgar, orpiment, stibnite, sphalerite, rhodochrosite, quartz, calcite.
The name is derived from the locality at Duranus, France.