Formula: FeAsS
Oxidation states: Fe2+As1-S1- (AM 87.1692-1698)
Specific gravity: 5.9 - 6.2
Hardness: 5½ - 6
Streak: Black
Colour: Tin white to steel white
Solubility: Arsenopyrite is moderately soluble in nitric acid but insoluble in hydrochloric and sulphuric acids

Pegmatites (sparingly)
Metamorphic environments
Hydrothermal environments

Arsenopyrite is the most common arsenic-containing mineral. It occurs with tin and tungsten ores in high-temperature hydrothermal deposits, associated with silver and copper ores, galena, sphalerite, pyrite and chalcopyrite. It is frequently associated with gold. It is found in contact metamorphic deposits, and disseminated in limestone.


At the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, arsenopyrite may occur in crystals to 2 mm coating löllingite masses. The Emmons pegmatite is an example of a highly evolved boron-lithium-cesium-tantalum enriched pegmatite (R&M 94.6.503).


chalcopyrite, arsenopyrite, CO2 and O2 to Fe-tennantite, siderite and sulphur
10CuFeS2 + 4FeAsS + 4CO2 + 8O2 = Cu10Fe2As4S13 + 4Fe(CO3) + 11/2S2
(CM 28.725-738)

chalcopyrite, arsenopyrite and pyrite to Fe-tennantite and troilite
10CuFeS2 + 4FeAsS + FeS2 = Cu10Fe2As4S13 + 13FeS
(CM 28.725-738)

chalcopyrite, arsenopyrite and sulphur to Fe-tennantite and pyrite
10CuFeS2 + 4FeAsS + 13/2S2 = Cu10Fe2As4S13 + 12FeS2
This reaction occurs at a comparatively low temperature (CM 28.725-738).

chalcopyrite, arsenopyrite and sulphur to Fe-tennantite and troilite
l0CuFeS2 + 4FeAsS + l/2S2 = Cu10Fe2As4S13 + l2FeS
(CM 28.725-738)

Common impurities: Ag,Au,Co,Sn,Ni,Sb,Bi,Cu,Pb

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