Acanthite
ID: 63
Acanthite
Chemical Formula
Ag₂S
Hardness (Mohs)
2-2.5
Crystal System
Monoclinic
Streak
Shining black
Luster
Metallic
Diaphaneity
Opaque
Color
Iron-black
Crystal Habit / Mode of Occurrence
Often occurs as pseudocubic or pseudo-octahedral crystals, also dendritic or massive.
Fun Facts
Acanthite is the low-temperature monoclinic polymorph of argentite. Argentite is the isometric form, stable above 177°C. Most "argentite" specimens are actually acanthite paramorphs after argentite.