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"very hard mineral," 1728, from Anglo-Indian, from Tamil kurundam "ruby sapphire" (Sanskrit kuruvinda), of unknown origin.
An extremely hard mineral occurring in many colors, either as shapeless grains or as rhombohedral crystals. It also occurs in gem varieties such as ruby and sapphire and in a dark-colored variety that is used for polishing and scraping. Corundum is found in igneous and carbonate rocks. Chemical formula: Al2O3.