Co*run"dum (k&osl;*rŭn"dŭm), n.; pl. Corundums (- dŭmz). [Also corindon.] [From Hind. kurand corundum stone.] (Min.) The earth alumina, as found native in a crystalline state, including sapphire, which is the fine blue variety; the oriental ruby, or red sapphire; the oriental amethyst, or purple sapphire; and adamantine spar, the hair-brown variety. It is the hardest substance found native, next to the diamond.

&fist; The name corundum is sometimes restricted to the non-transparent or coarser kinds. Emery is a dark-colored granular variety, usually admixed with magnetic iron ore.

• an extremely hard mineral, a form of aluminium oxide, that occurs in the form of the gemstones ruby and sapphire; it is used as an abrasive