4.4 - Where metals are found
Learn what an ore is and why most metals occur as compounds, while very unreactive metals such as gold can occur as uncombined elements in the Earth’s crust.
Metals in ores
Most metals are reactive enough to form compounds naturally. These compounds, including oxides, sulfides and carbonates, occur mixed with other materials in rocks in the Earth’s crust. Iron and aluminium are familiar examples of metals usually obtained from compounds in ores.
Ore
An ore is a rock containing enough metal, or a metal compound, for extracting the metal to be economically worthwhile.
Extraction means obtaining the metal from the ore. An ore is a source of metal; it is not necessarily a lump of pure metal. A rock with only traces of a metal may not be an ore because recovering so little metal would cost too much. Whether extraction is worthwhile can change as metal prices or extraction methods change.
Uncombined metals
Very unreactive metals form compounds less readily, so they can survive naturally as the metal element itself. Gold is a useful example; silver and platinum can also occur this way.
Uncombined element
An uncombined element is not chemically combined with another element. A metal occurring naturally in this form is called a native metal.
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