ARGENTITE is a cubic, high temperature from of silver sulfide (>173oC). Below this temperature, Argentite changes to Acanthite. Acanthite is the stable form.
The
dark, iron black mineral is the common massive form of Acanthite.
This is a
close-up view.
Crystals of
Argentite
CHEMISTRY Ag2S Silver sulfide
CRYSTALLOGRAPHY Monoclinic (pseudo orthorhombic)
CRYSTAL GROWTH AND HABITS Acanthite typically forms long prismatic crystals and is also massive.
COLOR AND OTHER OPTICAL PROPERTIES Iron black, opaque
HARDNESS 2 - 2.5
SPECIFIC GRAVITY 7.2 - 7.3
LUSTER Metallic
STREAK Black
BREAKABILITY Acanthite has uneven fracture and is somewhat sectile.
OCCURRENCE Acanthite is found in low temperature hydrothermal veins and in zones of secondary enrichment.
ASSOCIATED MINERALS Silver, Pyragyrite, Proustite, Galena, Sphalerite, Chalcopyrite, Quartz, Calcite