Minerals acanthite

Another important metal-excess sulfide with a complex structure is AgjS as the mineral acanthite, half of the silver atoms occur in a twofold,... 

Silver(I) sulfide occurs naturally as the minerals acanthite and argentitde, from which they can be extracted by grinding, crushing, and washing the mineral ore. The compound can also be prepared synthetically by passing hydrogen sulfide (H2S) gas through an aqueous solution of silver nitrate. 

Mineral Acanthite/Argentite, The." Amethyst Galleries. http //mineral.galleries.com/minerals/sulfides/acanthit/ acanthit.htm (accessed on November 5, 2005). 

The vein is composed of rhythmic banding of quartz layers and fine-grained sulfides such as argentite, acanthite, sphalerite, galena, pyrite and chalcopyrite, and elec-trum. The principal gangue minerals are quartz, calcite, adularia and interstratified chlorite/smectite. Minor minerals are inesite, johansenite, xonotlite and sericite. These gangue minerals except for quartz, adularia, calcite and sericite are not found in the wall rocks. 

Main opaque minerals are chalcopyrite, pyrite, pyrrhotite, sphalerite and bornite (Table 2.22). These minerals commonly occur in massive, banded and disseminated ores and are usually metamorphosed. Hematite occurs in red chert which is composed of fine grained hematite and aluminosilicates (chlorite, stilpnomelane, amphibole, quartz) and carbonates. The massive sulfide ore bodies are overlain by a thin layer of red ferruginous rock in the Okuki (Watanabe et al., 1970). Minor opaque minerals are cobalt minerals (cobaltite, cobalt pentlandite, cobalt mackinawite, carrollite), tetrahedrite-tennantite, native gold, native silver, chalcocite, acanthite, hessite, silver-rich electrum, cubanite, valleriite , and mawsonite or stannoidite (Table 2.22). 

Argentite is probably die most important primary silver mineral. However, it maintains its cubic (isometric) characteristic only above 179 C (354°F). Upon cooling, the inward structure inverts to a noil-isometric form, usually orthorhombic, yet retaining its original outward form. It is, therefore, a paramorph after argentite, known as acanthite. 

Mexico, the leading silver producer, obtains about half of its output from mines in which silver is the principal ore metal. Many of the mines are epithermal fissure veins, and most host a polymetallic assemblage whose exploitation is economically dependent on the high silver values. Although acanthite [Ag2S] and native silver predominate in some veins, in others much of the silver occurs in silver sulfosalts and as silver substitutions in tetrahedrite [(Cu,Fe,Ag)i2Sb4Si3] and other minerals. 

---