corundum
noun
co·run·dum kə-ˈrən-dəm 
: a very hard mineral that consists of aluminum oxide occurring in massive and crystalline forms, that can be synthesized, and that is used for gemstones (such as ruby and sapphire) and as an abrasive
Example Sentences
Recent Examples on the Web According to a new study, the night side is cold enough to form metal clouds of iron and corundum. 
Joshua Hawkins, BGR, 25 Feb. 2022 The temperature differences between the two sides of the planet also mean that the nightside is cool enough for metal clouds made of iron and corundum to form. Ashley Strickland, CNN, 21 Feb. 2022 Known for their red color, rubies are part of the corundum family of gemstones, which are gems that are compact and dense, according to the International Gem Society. Jordan Mendoza, USA TODAY, 27 Oct. 2021 Left side: 31 round diamonds, blue corundum stone and bricks and ivy silhouette. Kori Rumore, chicagotribune.com, 18 Oct. 2021 With a Mohs hardness score just a point shy of diamond’s, corundum becomes a red ruby through the timely addition of chromium atoms. Natalie Angier, New York Times, 11 Dec. 2017 After all, sapphires and rubies are built of the same basic mineral, corundum, a crystallized collaboration of aluminum and oxygen that would be transparent and colorless if not for some artful chemical doping. Natalie Angier, New York Times, 11 Dec. 2017 See More
Joshua Hawkins, BGR, 25 Feb. 2022 The temperature differences between the two sides of the planet also mean that the nightside is cool enough for metal clouds made of iron and corundum to form. Ashley Strickland, CNN, 21 Feb. 2022 Known for their red color, rubies are part of the corundum family of gemstones, which are gems that are compact and dense, according to the International Gem Society. Jordan Mendoza, USA TODAY, 27 Oct. 2021 Left side: 31 round diamonds, blue corundum stone and bricks and ivy silhouette. Kori Rumore, chicagotribune.com, 18 Oct. 2021 With a Mohs hardness score just a point shy of diamond’s, corundum becomes a red ruby through the timely addition of chromium atoms. Natalie Angier, New York Times, 11 Dec. 2017 After all, sapphires and rubies are built of the same basic mineral, corundum, a crystallized collaboration of aluminum and oxygen that would be transparent and colorless if not for some artful chemical doping. Natalie Angier, New York Times, 11 Dec. 2017 See More Word History
Etymology
Tamil kuruntam; akin to Sanskrit kuruvinda ruby
First Known Use
1804, in the meaning defined above
Medical Definition
corundum
noun
co·run·dum kə-ˈrən-dəm
: a very hard mineral Al2O3 that consists of alumina occurring in massive form and as variously colored crystals which include the ruby and sapphire