The pure metal is silvery white and light in weight, having a specific gravity of 2.7. One stable isotope (aluminum 47) occurs naturally, and six unstable isotopes are known.
In this process, ore that contains the aluminum, most often bauxite, is first purified to form a substance called alumina, which contains both aluminum and oxygen.
The alumina is placed in a bath of melted cryolite, whose constituents include fluorine and iron; fluorspar, a compound of calcium and fluorine, is added to lower the melting point.
The elemental aluminum that is produced by the Hall process has many uses because of its light weight, tensile strength, and good conductivity of heat and electricity.
Most notably, all of the modern aircraft that are flown by the military services and airlines have aluminum as their primary structural material.