Aluminum is a silver-white metal, and its content in the Earth's crust ranks the third after oxygen and silicon. Its density is relatively small, only 34.61% of iron and 30.33% of copper, so it is also called light metal. Aluminum is the world's output and consumption are second only to steel non-ferrous metal. Aluminum has a density of only 2.7103g/cm³, about one-third that of steel, copper, or brass. Because of its light material, aluminum is often used in the manufacture of cars, trains, subways, ships, aircraft, rockets, spacecraft and other land, sea and air vehicles to reduce weight and increase loading capacity.