Sylvanite

Sylvanite is a telluride mineral that represents a solid solution between gold telluride and silver telluride, commonly written with the approximate formula (Au, Ag)Te2. It occurs in hydrothermal ore veins and is often found together with other tellurides such as calaverite (AuTe2) and krennerite, as well as with native gold. The mineral forms metallic, brass- to silvery-brass masses, and crystals are rare and typically small, tabular or prismatic. It crystallizes in the monoclinic system and has a metallic luster.

In hand sample sylvanite is dense and lustrous, with a hardness on the Mohs scale around 2.5–3. Its specific gravity is generally high, typically in the range of about 7.8–8.3. The color is usually a brassy gold or pale gray metallic hue, and it may tarnish in air.

Sylvanite has historical and ongoing importance as an ore of gold in certain mining districts. Extraction typically involves froth flotation to produce a telluride concentrate, followed by roasting to oxidize the telluride and liberate the gold, and then cyanidation or smelting to recover the metal. Because telluride minerals can be refractory, processing often requires careful treatment to maximize gold recovery. Sylvanite remains a characteristic constituent of some high-grade telluride ore assemblages and helps to indicate the geological conditions of hydrothermal gold mineralization.