An ore is a natural combination of minerals from which metals can be extracted at a profit. Originally the term ore was applied only to metallic minerals, but the term now includes nonmetallic substances that have been deposited in rock after its formation. All metals come from ore deposits found in the Earth's crust.
Raw ores bear little resemblance to familiar metals such as chromium or nickel.
In most cases, the metals in the ores are not in the free, or pure, state. They are in chemical combination with other elements. They are combined with oxygen as oxides, with sulfur as sulfides, and with carbon and oxygen as carbonates. Ores also contain earthy materials such as sand and clay. These worthless substances are separated and discarded.