Although lead is seldom found uncombined in nature, its compounds are widely distributed throughout the world, principally in the ores galena, cerussite, and anglesite. Australia, the United States, Canada, and Russia are among the chief producers of lead. In the United States galena (a lead sulfide ore) is mined in southern Missouri, with some ore coming from the western states. The ore is concentrated by the flotation process and is then refined by electrolysis or by smelting. About one third of the lead used in the United States is so-called secondary lead, i.e., lead and lead alloys reclaimed chiefly from automobile batteries.