Ore is a mineral or rock that contains enough metal to make it worth mining. Ore deposits often occur in cracks of rocks called veins and in layers known as beds. Ore spread thinly in rock is disseminated ore. Worthless minerals mixed in with ore are called gangue.
There are two types of ores—native metals and compound ores. In native metals, the valuable mineral occurs as a pure metal. It is not chemically combined with other substances. Gold, silver, platinum, and copper often occur as native metals. In compound ores, the valuable metal is joined to other substances such as oxygen, sulfur, carbon, or silicon to form various chemical compounds. The ores of iron, aluminum, and tin are usually found joined with oxygen in compounds called oxides. Copper, lead, zinc, silver, nickel, and mercury are commonly found joined with sulfur in compounds called sulfides.
Metal is separated from ore in various ways. In a process called concentration, ore is crushed and ground so that metals separate from gangue. Metals can also be freed from ore and purified by smelting, in which ore is melted. Some metals can be dissolved out of ore by a process called leaching. In the electrolysis process, metals are separated by passing an electric current through a solution that contains metal atoms. See Metallurgy (Extractive metallurgy).
