Iron arsenide

Eisenarsenik, n. iron arsenide, specif. (Min.) Idllingite or leuocopyrite. 

Ferric arsenite is reduced to a slight extent when heated in an inert atmosphere 1 if heated in hydrogen under pressure it decomposes, forming iron arsenide, iron oxide and arsenious oxide.2... 

As is a metal found in the earth s crust, most commonly in the form of iron arsenide sulfide (FeAsS). Arsenic can also he found in the atmosphere as arsenic trioxide dusts, a by-product of industrial smelting operations (http //chemwiki.ucdavis.edu). Through erosion and dissolution, As can enter natural ground and surface waters. Once dissolved, it can take many forms, both organic and inorganic. 

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