Rollandite
Hydrated copper arsenate — a blue-green secondary mineral.
Intro adapted from Wikipedia (CC BY-SA).
Rollandite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Cu₃(AsO₄)₂·4H₂O.
It crystallizes in the orthorhombic crystal system (space group Pnma).
Key properties: Mohs hardness 4–4.5; specific gravity 3.9; Light green streak; Vitreous luster; optically biaxial.
IMA symbol Rol, IMA status: approved, named in 1998.
Found as a secondary mineral in small geodes.
It is found associated with Olivenite, conichalcite, clinotyrolite, cornubite, kolfanite, pharmacosiderite, gerhardtite, atacamite, gilmarite, wallkilldellite-Fe, cuprite, domeykite.
The mineral was named to honor Pierre Rolland (b. 1940), who collected the material studied.