The effluent from the tailings from the mining of sulfidic minerals has been described as "the largest environmental liability of the mining industry". These tailings contain large amounts of pyrite (FeS) and Iron(II) sulfide (FeS), which are rejected from the sought-after ores of copper and nickel, as well as coal. Although harmless underground, these minerals are reactive toward air in the presence of microorganisms, which if not properly managed lead to acid mine drainage.