Polishing powder is usually composed of cerium oxide, alumina, silicon oxide, iron oxide, zirconia, chromium 

oxide and other components. Different materials have different hardness and different chemical properties in 

water, so the use occasions are different. Alumina and chromium oxide have a Mohs hardness of 9, ceria and 

zirconia 7, and iron oxide is even lower. Cerium oxide is widely used in glass polishing because of its high 

chemical activity and comparable hardness with silicate glass.