ARGENTITE  , a

mineral which belongs to the galena group, and is cubic silver sulphide (Ag2S) . It is occasionally found as uneven cubes and octahedra, but more often as dendritic or earthy masses, with a blackish lead-grey colour and metallic lustre . The cubic cleavage, which is so prominent a feature in galena, is 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 Mexico and in the Comstock lode in Nevada, it forms an important ore of silver . The mineral was mentioned so long ago as 1529 by G . Agricola, but the name argentite (from the Lat. argentum, " silver ") was not used till 2845 and is due to W. von Haidinger . Old names for the species are Glaserz, silver-glance and vitreous silver . A cupriferous variety, from Jalpa in Tabasco, Mexico, is known as jalpaite . Acanthite is a supposed dimorphous form, crystallizing in the orthorhombic system, but it is probable that the crystals are really distorted crystals of argentite . (L . J .