The Argentite reference article from the English Wikipedia on 24-Apr-2004
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Argentite

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Argentite, a mineral which belongs to the galena group, is cubic silver sulphide (Ag1S). It is occasionally found as unen cubes and octahedra, but more often as dendritic or earthy isses, 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 d has a shining streak; hardness 25, specific gravity 7.3. It :urs in mineral veins, and when found in large masses, as in is exico and in the Comstock lode in Nevada, it forms an imrtant ore of silver. The mineral was mentioned 1529 by G. Agricola, but the name argentite (from the Lat. Ientum, 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 is a supposed ???norphous form, crystallizing in the orthorhombic system, it is probable that the crystals are really distorted crystals of argentite.

This article incorporates text from the public domain 1911 Encyclopædia Britannica.