Nagyágite [Pb5Au(Te, Sb)4S5-8] is a rare sulfide mineral with a known occurrence associated with gold ores. It is a mineral that is a sulfide of lead, gold, tellurium, and antimony. It is a monoclinic (pseudotetragonal) telluride, antimonide, and sulfide of lead and gold, occurring as dark grey tabular crystals.
It was first described in 1845 for an occurrence at the type locality of the Nagyág mine, Săcărâmb, Hunedoara County, Romania. This mineral gets its name from the type locality at Sacarîmb, also called Nagyág, in Romania.
General Information
- Category: Sulfosalt mineral
- Formula: (repeating unit) [Pb5Au(Te,Sb)4S5-8]
- Crystal system: Monoclinic
- Crystal class: Prismatic (2/m) (same H-M symbol)
- Colour: Blackish lead-grey; pale grey in polished section.
Properties
Nagyágite crystals are opaque, monoclinic and dark grey to black coloured. It is a mineral of blackish lead-gray color and metallic luster, generally of a foliated massive structure; foliated tellurium. It has a hardness of 1.5 on the Mohs scale with thin flexible lamellae much like Molybdenite.
- Crystal habit: Tabular crystals (often bent), also massive granular, pseudotetragonal
- 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
Occurrences
Nagyagite is an uncommon mineral that occurs in epithermal hydrothermal gold and tellurium bearing deposits. It occurs in gold–tellurium epithermal hydrothermal veins. It can be found in, additionally, the Czech Republic, Kazakhstan, Armenia, Zimbabwe, the United States, Canada, Argentina, Australia, New Zealand, Japan, and Fiji among others.
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.
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