corundum

American  

[kuh-ruhn-duhm] / kəˈrʌn dəm /

noun

1. a common mineral, aluminum oxide, Al 2 O 3 , notable for its hardness: transparent varieties, as sapphire and ruby, are used as gems, other varieties as abrasives: often made synthetically.

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corundum British  

/ kəˈrʌndəm /

noun

1. a white, grey, blue, green, red, yellow, or brown mineral, found in metamorphosed shales and limestones, in veins, and in some igneous rocks. It is used as an abrasive and as gemstone; the red variety is ruby, the blue is sapphire. Composition: aluminium oxide. Formula: Al 2 O 3 . Crystal structure: hexagonal (rhombohedral)

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corundum Scientific  

/ kə-rŭn′dəm /

1. 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: Al ₂ O ₃ .

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Etymology

Origin of corundum

1720–30; < Tamil kuruntam; akin to Sanskrit kuruvinda ruby

Example Sentences

If the quartz can’t scratch the specimen, it might be beryl or corundum, which are harder than quartz.

From Scientific American • Sep. 3, 2021

The Bronco mane and eyeball were created from orange sapphires while the head features pave-set diamonds and custom-cut corundum blue stone.

From Washington Times • Jun. 12, 2016

For example apatite is about three times harder than fluorite and diamond is three times harder than corundum.

From Textbooks • Jan. 1, 2015

Rubies and sapphires, which are both made of the same mineral, corundum, are “quite durable,” according to John Watkins, an independent goldsmith in Lake Nacimiento, California.

From BusinessWeek • May 31, 2011

In its natural state, it is the mineral corundum.

From Webster's Unabridged Dictionary by Webster, Noah

Related Words

• gem
• jewel
• rhinestone