Eleomelanite
Eleomelanite is an IMA-recognized mineral species in the sulfate class, with the chemical formula (K₂Pb)Cu₄O₂(SO₄)₄.
It crystallizes in the monoclinic crystal system (space group P2_1/n).
Key properties: Mohs hardness 3; specific gravity 3.79; Dark green streak; Oleaginous on crystal faces, vitreous on cleavage surfaces luster; optically biaxial.
IMA symbol Elm, IMA status: approved, named in 2015.
Forms as a sublimate at an active volcanic fumarole.
It is found associated with Euchlorine, fedotovite, wulffite, chalcocyanite, dolerophanite, dravertite, hermannjahnite, alumoklyuchevskite, klyuchevskite, piypite, cryptochalcite.
Its name comes from the Greek eleon for ‘oil’, and melas for ‘black’, for its black color and oleaginous luster on crystal faces that is uncommon for sulfate minerals.