An opaque mineral, Ag2S; density 7.2–7.4 g/cm3; hardness 2–2.5; monoclinic; lead grey or black; lead grey streak; metallic lustre; crystals pseudo-cubic, pseudo-octahedral, or monoclinic; no cleavage; fracture sub-conchoidal; widely distributed in silver deposits and zones of secondary enrichment. It is the low-temperature modification of silver sulphide, and all natural silver sulphide at room temperature is acanthite.