Oyonite occurs as black subhedral to anhedral crystals, up to 100 μm in length. Streak is black, and the luster is metallic. Andorite-like minerals occurring with orpiment on calcite. The crystals are not a single phase but a mixture of mainly different andorite-group minerals (i.e., oyonite, menchettiite, …). The width is 1 mm. Photo by Christian Rewitzer. — Photo: Christian Rewitzer · CC BY 4.0
Oyonite
Oyonite is an IMA-recognized mineral species in the sulfosalt class, with the chemical formula Ag₃Mn₂Pb₄Sb₇As₄S₂₄.
It crystallizes in the monoclinic crystal system (space group P2_1/n). It is a member of the Lillianite structural group.
Key properties: Mohs hardness 3–3.5; specific gravity 5.275; Black streak; Metallic luster.
IMA symbol Oyo, IMA status: approved, named in 2018.
Found in a hydrothermal vein, lead-zinc-silver deposit of sulfide and sulfosalt minerals, and abundant alabandite and manganese calcium silicates in carbonate rock.
It is found associated with Orpiment, tennantite-tetrahedrite, menchettiite, other minerals of the system Pb-Ag-Sb- Mn-As-S, calcite.
The name refers to the region that produced the first specimen, Oyon district, Peru.