ACANTHITE (from the Greek word "akantha", which means "thorn, needle"; is named after the form of the crystals * EN: acanthite; DE: Akanthit; FR: acanthite; ES: acantita; RU: акантит) is the mineral of the class of the sulfides, the polymorph modification of Ag2S, which is stable below 173 degrees Celsius (argentite is stable above this temperature). It contains 87% of Ag, and Cu, Fe, Zn, Sb impurities. It crystallizes in the monoclinic system; the crystalline structure is coordinated. It forms the films, earthy aggregates ("Silver Black"), solid masses, less often fine crystals. There are characteristic the lamellar twins, which often are polysynthetic (the result of the transition of the argentite into the acanthite). It also occurs in the form of the paramorphs by argentite, which are having the form of the dendrites, skeletal, mesh-like, wire-like, spiciform crystals, and incorrect isolations. The colour is iron-black, to lead-gray. The shine is metallic, dims in the light. The hardness is 2-2.5; it is malleable. The density is 7300 ± 100 kilograms per cubic metre. Acanthite is the low-temperature hydrothermal or supergene mineral (is is formed in the zone of the secondary sulfide benefication of the silver and polymetallic deposits).

Acanthite is the valuable silver ore. It is beneficiated mainly by the flotation. The collectors are: the ethyl xanthate, the cresyl dithiophosphate in the alkaline medium, the mixture of the dithiophosphates, etc.; the foam forming agents are: the pine oil, cresol, etc.; the regulators of the medium are: CaO, Na2CO3; the depressors are: cyanides, Na2S, tannin, quebracho (during the high levels of consumption).