This extremely light metal is also very abundant-it makes up one-twelfth of the Earth's crust. Its ores are mainly bauxites in which aluminium is combined with oxygen, sand, titanium and other substances. The bauxite is first refined into alumina, a purer form of aluminium oxide, by the Bayer process. The alumina is then separated into aluminium and oxygen by electrolysis. This is done at almost 1,000 C on a bath of molten.