Nagyágite

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Nagyágite
Nagyagite-163939.jpg
Nagyágite from Nagyág (Săcărâmb), Romania (image width: 1.5 mm)
General
Category Sulfosalt mineral
Formula
(repeating unit)
Pb5Au(Te,Sb)4S5-8[1] or AuPb(Sb,Bi)Te2-3S6[2] or (Te, Au)Pb(Pb, Sb)S2[3]
Strunz classification 2.HB.20a
Dana classification 02.11.10.01
Crystal system Monoclinic
Prismatic class
Identification
Colour Blackish lead-grey; pale grey in polished section
Crystal habit Tabular crystals (often bent), also massive granular, pseudotetragonal
Crystal symmetry Monoclinic
H-M symbol: (2/m)
Space group: P21/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
Lustre Metallic, bright on fresh cleavage
Streak Blackish lead-grey
Diaphaneity Opaque
Specific gravity 7.35–7.49
Pleochroism Weak
References [1][2][3]

Nagyágite (Pb5Au(Te,Sb)4S5-8) 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.[1][2]

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.[3]

References[edit]