Formula: Ag2S sulphide
Specific gravity: 7.3
Hardness: 2
Streak: Black
Colour: Lead grey
Solubility: Acanthite is slightly soluble in hydrochloric acid and sulphuric acid.
Common impurities: Se

Hydrothermal environments

Acanthite is a primary silver mineral that occurs in epithermal (low temperature) hydrothermal silver ore veins. It may also be of secondary origin. At atmospheric pressure, acanthite is stable below 173°C. Above 173°C the structure changes to produce crystals of twinned acanthite known as argentite. Argentite is unstable below 173°C, and if the temperature drops below this level it will change back to acanthite.


At the Mount Lyell Mines, Queenstown district, West Coast municipality, Tasmania, Australia, acanthite pseudomorphs after argentite have been found in a vein of chalcocite, bornite and tetrahedrite between massive pyrite and hematite bodies (AJM 21.2.21).

At the Old Hope of God pit, Freiberg, Saxony, Germany, acanthite pseudomorphs after galena have been found with proustite and baryte (KL p126).

At the San Juan de Rayas mine, Guanajuato, Mexico, acanthite forms paramorphs after argentite. At the same locality acanthite-chalcopyrite forms pseudomorphs after polybasite (KL p123-124)>.

At the Santa Catarina mine, Guanajuato, Mexico, acanthite forms pseudomorphs after pyrargyrite (KL p125)>.

Back to Minerals