Arsenic, Native

a mineral of the class of native elements; chemical symbol As. It usually contains admixtures of antimony, sulfur, iron, silver, nickel, and—less frequently—bismuth and vanadium. Native arsenic contains up to 98 percent As. It crystallizes in the trigonal system. Crystals, which are small rhombohedrons of pseudocubic habit, are very rare; solid granular masses in the form of botryoidal sinters and crusts are more common. Native arsenic has a tin-white color on fresh fracture; weathered surfaces of the mineral are black. Its hardness on Mohs’ scale is 3.0–3.5; the density is 5, 630–5, 800 kg/m³. The mineral is brittle.

Native arsenic is usually formed from hot aqueous solutions and is found in association with silver, cobalt, and nickel minerals, as well as with galena, pyrite, and antimonite. It oxidizes upon weathering and is subsequently converted into arsenolite, As₂O₃. Native arsenic usually does not form large deposits.