ore
An ore is a type of mineral or rock which has a high enough concentration of a desirable element such that it's economical to extract that desired element. This means that the actual concentration of metal in an ore varies quite dramatically depending upon the metal. For instance, Bauxite, which is the ore for aluminum contains approximately 15% to 25% aluminum. But for gold, it's not uncommon to profitably extract 1 ounce of gold from several tons of rock.