Nagyágite
A rare dark 'black tellurium' sulfosalt of lead, gold, tellurium and antimony — associated with gold ores.
Intro adapted from Wikipedia (CC BY-SA).
Nagyágite is an IMA-recognized mineral species in the sulfosalt class, with the chemical formula [Pb₃(Pb,Sb)₃S₆](Au,Te)₃.
It crystallizes in the monoclinic crystal system (space group P2_1/m).
Key properties: Mohs hardness 1.5; specific gravity 7.35–7.49; Blackish lead-gray streak; Metallic, bright on fresh cleavage luster.
IMA symbol Ngy, grandfathered status — known before the IMA’s founding, named in 1845.
Found in Au–Te-bearing epithermal hydrothermal veins.
It is found associated with Altaite, petzite, stutzite, sylvanite, tellurantimony, coloradoite, krennerite, arsenic, gold, proustite, rhodochrosite, arsenopyrite, sphalerite.
The name refers to the Săcărı̂mb (Nagyág), Romania locality.