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

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

On the Mohs scale, which measures minerals’ hardness from 1 to 10, corundum ranks at 9.

From BusinessWeek • May 31, 2011

When corundum presents the bluish tint of typical aquamarine, it is often termed Oriental aquamarine.

From Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 "Apollodorus" to "Aral" by Various

Related Words

• gem
• jewel
• rhinestone