Alumina

Alumina can be extracted from natural minerals such as bauxite, garnet, kyanite, alum, kaolin, clay, etc. Natural colorless alumina crystals are called corundum, and alumina can also be artificially synthesized through high-temperature firing, known as artificial corundum. Corundum has a high hardness and can be used to make bearings in machinery or watches. Aluminum oxide can be used as a high-temperature refractory material, as well as for making refractory bricks, crucibles, porcelain, artificial rubies, etc. Aluminum oxide is also used as an insulation material.