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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.

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)

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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 .

Etymology

Origin of corundum

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

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

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

From a chemical analysis of a sample it has been calculated that the emery contained 52.4% of corundum, 32.1 of magnetite, 11.5 of tourmaline, 2 of muscovite and 2 of margarite.

From Encyclopaedia Britannica, 11th Edition, Volume 9, Slice 3 "Electrostatics" to "Engis" by Various

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.