Aluminium (or aluminum) is a chemical element in the boron group with symbol Al and atomic number 13. It is silvery white, and it is not soluble in water under normal circumstances. Aluminium is the third most abundant element, and the most abundant metal, in the Earth’s crust. It makes up about 8% by weight of the Earth’s solid surface. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments.