ARSENOPYRITE, arsenical pyrite (from the words "arsenicum" (the Latin name for arsenic) and pyrite * EN: arsenopyrite, arsenical pyrite, mispickel, white pyrite, white mundic; DE: Arsenopyrit, Arsenkies, Mißpickel, Giftkies; FR: arsénopyrite, arsénosidérite, mispickel; ES: arsenopirita, mispiquel; RU: арсенопирит), is the mineral of the class of sulphides, FeAsS. The actual content of As is 40-49%. The impurities are: Co, Ni, Mn, Zn, Sb, Se. There exists the isomorphic series: from arsenopyrite (up to 3% of CoO), to danaite (3-12% of CoO), to glaucodot (more than 12% of CoO, the ratio Co:Fe is ~ 1:1). It often contains the tiniest inclusions of the native gold (auriferous arsenopyrite). It crystallizes into the monoclinic or triclinic crystal system. The crystal structure is of the coordinative type, there is within its base the densest packing of the AsS3- radicals. It forms the long, less often short, prismatic, with characteristical rhombic cross-section, crystals, stellate intergrouths, columnar and granular aggregates. The colour is tin-white, and steel-gray at the fracture. Often there is observed the yellow iridescence. The lustre is metallic. The hardness is 5.5-6.0, it is brittle. The density is 6100±100 kilograms per cubic metre.

Arsenopyrite is the typical mineral of the high-temperature and medium-temperature hydrothermal deposits, including the ones which often contain the gold ore. Arsenopyrite is the main source for the obtainment of arsenic and its compounds (see the "Arsenic ores" article), they extract cobalt from the cobalt-containing arsenopyrite. The auriferous arsenopyrite belongs to the list of the gold ores. The major method of beneficiation is flotation. The sorbents are the xanthates within the acidic environment; the regulators of the environment are the soda, sulfuric acid, lime; the activators are the cations of copper; the depressors are the oxidants (calcium hypochlorite, permanganate, chromate, oxygen from the air, pyrolusite, lime with the salts of ammonium, cyanide). The selection from pyrite is achieved during the activation of arsenopyrite with ions of copper, and during the flotation within the calcareous environment.