solid homogeneous inorganic substances occurring in nature having a definite chemical composition

a hard grey-black mineral consisting of corundum and either hematite or magnetite; used as an abrasive (especially as a coating on paper)

any of various forms of aluminum oxide occurring naturally as corundum

a transparent deep red variety of corundum; used as a gemstone and in lasers

a precious transparent stone of rich blue corundum valued as a gemstone

a hard grey-black mineral consisting of corundum and either hematite or magnetite; used as an abrasive (especially as a coating on paper)