Ruda Plant / Aclk Sa L Ai Dchcsewii4u3wplb1ahxrj2gjhwsydd0yababggj3zg Sig Aod64 2skx2f2r4tsdskm Owreue1v1 Fa Adurl Ctype 5 - Calcined alumina is a synthetic corundum, which is a very hard material (9 on the mohs hardness scale).calcined alumina is crushed, separated by size, and used as an abrasive.