Granular rock consisting of a mixture of the mineral corundum (aluminum oxide, Al 2 O 3 ) and iron oxides such as magnetite (Fe 3 O 4 ) or hematite (Fe 2 O 3 ).
It is a dark, dense substance that looks much like iron ore. Turkey is the world's major producer. Long used as an abrasive or polishing material, particularly in sandpapers, it has largely been replaced by synthetic materials such as alumina. Its largest application now is as a nonskid material in floors, stair treads, and pavements.