Nagyágite

Nagyágite
240px Nagyágite from Nagyág (Săcărâmb), Romania (image width: 1.5 mm)
General
Category	Sulfosalt mineral
Formula (repeating unit)	Pb5Au(Te,Sb)4S5-8 or AuPb(Sb,Bi)Te2-3S6 or (Te, Au)Pb(Pb, Sb)S2
Strunz classification	02.HB.20a
Dana classification	02.11.10.01
Identification
Colour	Blackish lead-grey; pale grey in polished section
Crystal habit	Tabular crystals (often bent), also massive granular
Crystal system	Monoclinic, pseudotetragonal. Point Group: 2/m.
Twinning	Crossed twin lamellae observed on (001) sections
Cleavage	Perfect on {010}, excellent on {101}
Fracture	Hackly
Tenacity	Flexible, slightly malleable
Mohs scale hardness	1.5
Luster	Metallic, bright on fresh cleavage
Streak	Blackish lead-grey
Diaphaneity	Opaque
Specific gravity	7.35–7.49
Pleochroism	Weak
References

Nagyágite (Pb₅Au(Te,Sb)₄S_5-8) is a rare sulfide mineral with known occurrence associated with gold ores. Nagyágite crystals are opaque, monoclinic and dark grey to black coloured.

It was first described in 1845 for an occurrence at the type locality of the Nagyág mine, Săcărâmb, Hunedoara County, Romania.

It occurs in gold–tellurium epithermal hydrothermal veins. Minerals associated with nagyágite include: altaite, petzite, stutzite, sylvanite, tellurantimony, coloradoite, krennerite, native arsenic, native gold, proustite, rhodochrosite, arsenopyrite, sphalerite, tetrahedrite, calaverite, tellurobismuthite, galena and pyrite.