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

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

alumina, aluminium oxide, aluminum oxide - any of various forms of aluminum oxide occurring naturally as corundum

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

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