Ore smelting. In nature, iron, copper, lead, nickel and other metals are found in impure states called ores, often oxidized and mixed in with silicates of other metals.
Lower-grade sources of iron ore generally require beneficiation, using techniques like crushing, milling, gravity or heavy media separation, screening, and silica ...
In the 18th century, diamond deposits were discovered in Brazil in small quantities, and later in Australia, Russia, and the United States.