The most abundant metal element in the earth's crust is 8.3%. It is mainly composed of aluminosilicate ore, bauxite and cryolite. Alumina is a kind of white amorphous powder, which has many variants, among which the most familiar ones are α - Al Е o ₃ and β - Al Е o ₃. The corundum in nature belongs to α - Al Е o ₃. Its hardness is next to that of diamond. It has high melting point and is resistant to acid and alkali. It is often used to make some bearings, abrasives and refractories. Such as corundum crucible, can withstand 1800 ℃ high temperature. Al ₂ o ₃ has a variety of colors due to the presence of different impurities. For example, if there is trace Cr (III) in red, it is called ruby; if there is Fe (II), Fe (III) or Ti (IV), it is called sapphire.

Aluminum is a light metal, chemical symbol is al, atomic number: 13. The content of aluminum in the earth's crust is second only to that of oxygen and silicon, ranking third. It is the most abundant metal element in the earth's crust, and its reserve ranks second in the metal. In the category of metal, it is the second largest category after steel.