The most abundant metal elements in the earth's crust are 8.3%. It is mainly composed of aluminosilicate ore, bauxite and cryolite. Alumina is a kind of white amorphous powder. There are many varieties of alumina, among which the most familiar ones are α - Al к o ? and β - Al к o ?. Corundum, which exists in nature, belongs to α - Al ? o ?. Its hardness is second only to diamond, with high melting point and acid alkali resistance. It is often used to make some bearings, abrasives and refractories. For example, corundum crucible can withstand high temperature of 1800 ℃. Because of different impurities, Al Ψ o ? has many colors. For example, the ruby containing trace Cr (III) is red, and the sapphire containing Fe (II), Fe (III) or Ti (IV) is sapphire.

Aluminum is a light metal, chemical symbol for Al, atomic number: 13. The content of aluminum in the earth's crust is second only to oxygen and silicon, ranking the third. It is the most abundant metal element in the earth's crust, and its reserves rank the second among the metals. Among the metal varieties, it is the second largest type of metal after steel.