Arsenopyrite is the most common arsenic mineral and gets its name from the combination of its former name: aresenical pyrites. Its color is silver-white to steel-gray on freshly broken surfaces. It yields a garlic odor when heated and the fumes can be toxic. It may tarnish to form an iridescent layer. Although arsenic has a reputation for being poisonous to humans, complex compounds are actually used in the treatment of disease caused by microorganisms.