Argentite, a mineral which belongs to the galena group, is cubic silver sulfide (Ag2S). It is occasionally found as uneven cubes and octahedra, but more often as dendritic or earthy masses, with a blackish lead-grey color and metallic lustre. The cubic cleavage, which is so prominent a feature in galena, here present only in traces. The mineral is perfectly sectile and has a shining streak; hardness 2.5, specific gravity 7.3. It occurs in mineral veins, and when found in large masses, as in is Mexico and in the Comstock Lode in Nevada, it forms an important ore of silver. The mineral was mentioned 1529 by G. Agricola, but the name argentite (from the Lat. argentum, silver) was not used till 1845 and is due to W. Haidinger. Old names for the species are Glaserz, silver-glance and vitreous silver. A cupriferous variety, from Jalpa in Mexico, is known as jalpaite.
Acanthite, also Ag2S, crystallizes in the monoclinic system and is the stable form below 177oC. As argentite cools below that temperature its cubic form is distorted to the monclinic form of acanthite.