Aluminium, also spelt aluminum, is the most common metal in the world, and the third most common element (after oxygen and silicon). It is durable and lightweight, and is a very important metal for making planes out of. Aluminium is highly reactive and you cannot find pure aluminium in the same way you can find pure gold or copper, so it was once considered a rare precious metal. It is a very energy intensive process to refine aluminium. Aluminium is used for building (particularly frames for doors and windows) and vehicle construction, household aluminium foil, masts on ships, walking sticks, and lots of household utensils and appliances.