Acanthite
Image: <bdi><a href="https://www.wikidata.org/wiki/Q56247090" class="extiw" title="d:Q56247090"><span title="mineral collector and dealer">Robert M. Lavinsky</span></a></bdi> (CC BY-SA 3.0)
Mineral NameAcanthite
Chemical FormulaAg₂S
Mohs Hardness2
Crystal Systemmonoclinic
Lustermetallic
Streak Colorblack, shiny
Cleavageindistinct/poor
Fractureconchoidal to uneven
Specific Gravity7.2
Colorslead-gray, black
Transparencyopaque
Type LocalityJáchymov (St Joachimsthal), Krušné Hory Mts, Karlovy Vary Region, Bohemia
Mineral GroupSulfides
Usessilver ore, collector
Associated Mineralsnative silver, proustite, pyrargyrite, galena, sphalerite, calcite, quartz
Rarityuncommon
Description
This specimen displays acanthite as a dark, greenish-gray to black botryoidal or granular crust covering a lighter matrix. The surface has a dull metallic to earthy appearance.
Geological Context
Acanthite is a primary silver sulfide mineral typically found in low-temperature hydrothermal veins, often associated with native silver and other silver-bearing minerals. It forms from the alteration of argentite at temperatures below 173°C.
