Acanthite
Image: <a href="//commons.wikimedia.org/wiki/User:Iifar" title="User:Iifar">Ivar Leidus</a> (CC BY-SA 4.0)
Mineral NameAcanthite
Chemical FormulaAg₂S
Mohs Hardness2.5
Crystal Systemmonoclinic
Lustermetallic
Streak Colorblack
Cleavageindistinct on {010}
Fractureconchoidal
Specific Gravity7.2
Colorsdark gray, black, bluish-green (patina)
Transparencyopaque
Type LocalityImiter mine, Jbel Saghro, Tinghir, Drâa-Tafilalet, Morocco
Mineral GroupSulfides
Usessilver ore, collector
Associated Mineralsnative silver, proustite, pyrargyrite, galena, quartz
Rarityuncommon
Description
This specimen displays crystallized acanthite with a complex, spiky, and somewhat arborescent habit, exhibiting a dark gray to black metallic luster with subtle hints of bluish-green patina.
Geological Context
Acanthite is a common low-temperature silver sulfide mineral, often forming in hydrothermal veins and as a secondary mineral in silver deposits. It is the stable form of Ag₂S below 173°C, frequently pseudomorphing the high-temperature cubic argentite.
