Johillerite Locality: Second scoria cone, Northern Breakthrough (North Breach), Great Fissure eruption (Main Fracture), Tolbachik volcano, Kamchatka Oblast', Far-Eastern Region, Russia Field of view 4 mm. — Photo: Leon Hupperichs · CC BY-SA 3.0
Johillerite
Johillerite is an IMA-recognized mineral species in the arsenate class, with the chemical formula NaCuMgMg₂(AsO₄)₃.
It crystallizes in the monoclinic crystal system (space group C2/c). It is a member of the Alluaudite structural group.
Key properties: Mohs hardness 3; specific gravity 4.15; White to very pale violet streak; Vitreous luster; optically biaxial.
IMA symbol Jhl, IMA status: approved, named in 1980.
Found as a very rare secondary mineral in oxidized copper ore.
It is found associated with Cuprian adamite, conichalcite, chalcocite, tennantite.
The mineral was named to honor Professor Johannes-Erich Hiller (1911–1972), mineralogist, University of Stuttgart, Stuttgart, Germany.