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

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Example Sentences

See Examples For:

corundum

Diamond defines a hardness of 10 and is actually about four times harder than corundum, which is 9.

From Textbooks ● Jan. 1, 2017

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

It’s also a bonza industrial abrasive, and clear slices of synthetic corundum are used to make bullet-proof “glass.”

From Scientific American ● Apr. 14, 2012

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

How to Point a Pencil.—Rub the pencil to a point in the groove of a corundum file.

From The Evolution of Photography With a Chronological Record of Discoveries, Inventions, etc., Contributions to Photographic Literature, and Personal Reminescences Extending over Forty Years by John Werge

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Related Words

• gem
• jewel
• rhinestone

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