THE MINERAL NAGYAGITE

Chemistry: AuPb(Sb, Bi)Te_{2 - 3}S₆, Gold Lead Antimony Bismuth Iron Tellurium Sulfide
Class: Sulfides
Subclass: Sulfosalts and Tellurides
Uses: As a very minor ore of gold and as mineral specimens.
Specimens

Nagyagite's chemistry is golden! Nagyagite is one of only a few minerals that are composed of gold. Gold does not often combine with other elements and seems to prefer an existance as elemental, native gold. But there are a few gold minerals and most of those are tellurides, like nagyagite. The two most common and better known gold tellurides are calaverite and sylvanite.

All three minerals are found in relative abundance at a classic gold locality; Sacaramb, Transylvania, Romania. This is the type locality for nagyagite (from where it was first described). Sacaramb was formerly named Nagyag, hence the name for nagyagite. The Sacaramb gold mines are the type localities for several rare and classic gold and silver tellurium minerals such as krennerite, muthmannite, petzite and stutzite. Nagyagite is found here and at other localities in hydrothermal veins where it forms with gold, calaverite, sylvanite and other tellurides. Nagyagite is sometimes referred to as "foliated telluride" because of its foliated crystal habits. Another name for nagyagite is "black tellurium" for its color and tellurium content.

PHYSICAL CHARACTERISTICS:

Color is a dark lead gray to black.
Luster is metallic.
Transparency: Crystals are opaque.
Crystal System: Orthorhombic (pseudotetragonal).
Crystal Habits include platy to tabular crystals as well as foliated to micaceous masses.
Cleavage: perfect in one direction (basal).
Fracture: hackly.
Hardness is 1 - 1.5
Specific Gravity is 7.4 - 7.6 (much heavier than average for metallic minerals)
Streak is dark gray.
Associated Minerals include quartz, krennerite, hessite, native gold calaverite and sylvanite.
Notable Occurrences include the type locality of Sacaramb (formerly Nagyag, hence the name), Transylvania, Romania as well as Kalgoorlie, Western Australia; Washburn Mine, Sunshine and Gold Hill, Boulder County, Colorado; Dorleska Mine, Trinity County and in Shasta and Calaveras Counties, California and Kings Mountain Mine, Gaston County, North Carolina, USA.
Best Field Indicators are crystal habit, color, softness, locality, associations and density.