Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al and its atomic number is 13. It is not soluble in water under normal circumstances. Aluminium is the most abundant metal in the Earth's crust and the third most abundant element after oxygen and silicon. It makes up about 8% by weight of the Earth's solid surface. Aluminium metal is too reactive chemically to occur in nature.