Mineral Species: Acanthite

Chemical Formula: Ag2S

Chemical Name: Silver Sulphide

Mineral Class: Sulphide

Mineral Notes: Acanthite is the second most important source after argentiferous Galena. It occurs in low-temperature sulfide veins and in zones of secondary enrichment. It has the same chemical content as Argentite but a different crystal structure. The two minerals are therefore known as polymorphs. The crystals are often distorted and group together into intricate arborescent (branching) structures.

Description: Two clusters of Acanthite crystals on Quartz matrix. Individual crystals are well-formed, black-grey and have a distinct metallic luster. Below the Quartz is a dense layer of further granular Acanthite. In plces this shows a strong purple irridescence. Possibly because of the presence of some copper in the ore. A very good specimen from a classic location.

Location: Zacatecas, Mexico.