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The Collaborative International Dictionary

Corundum \Co*run"dum\ (k[-o]*r[u^]n"d[u^]m), n.; pl. Corundums (k[-o]*r[u^]n"d[u^]mz). [Also corindon.] [From Hind. kurand corundum stone.] (Min.) The mineral alumina ( Al2O3), as found native in a crystalline state. Transparent varieties are used as gemstones, including sapphire, which is the fine blue variety; the oriental ruby, or red sapphire; the oriental amethyst, or purple sapphire; and adamantine spar, the hair-brown variety. It is the hardest substance found native, next to the diamond.

Note: The name corundum is sometimes restricted to the non-transparent or coarser kinds. Emery is a dark-colored granular variety, usually admixed with magnetic iron ore.

Douglas Harper's Etymology Dictionary

"very hard mineral," 1728, from Anglo-Indian, from Tamil kurundam "ruby sapphire" (Sanskrit kuruvinda), which is of unknown origin.


n. (context mineral English) An extremely hard mineral, a form of aluminum oxide with the chemical formula aluminum2oxygen3, that occurs in the form of the gemstones sapphire and ruby; it is used as an abrasive.


n. very hard mineral used as an abrasive [syn: corundom]


Corundum is a crystalline form of aluminium oxide typically containing traces of iron, titanium, vanadium and chromium. It is a rock-forming mineral. It is one of the naturally transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red and padparadscha if pink-orange. All other colors are called sapphire, e.g., "green sapphire" for a green specimen.

The name "corundum" is derived from the Tamil word Kuruvindam or Sanskrit word Kuruvinda meaning ruby.

Because of corundum's hardness (pure corundum is defined to have 9.0 Mohs), it can scratch almost every other mineral. It is commonly used as an abrasive on everything from sandpaper to large machines used in machining metals, plastics, and wood. Some emery is a mix of corundum and other substances, and the mix is less abrasive, with an average Mohs hardness of 8.0.

In addition to its hardness, corundum is unusual for its density of 4.02 g/cm, which is very high for a transparent mineral composed of the low- atomic mass elements aluminium and oxygen.

Usage examples of "corundum".

It's technically corundum, but too poor a quality to hold a decent spell.

Rowe was returning my stone with his appraisal: it was corundum (sapphire and ruby are both corundum), but of a cheap grade imported from India for fifty cents a carat and sold to gullible tourists in places like North Carolina as local stones for five to ten dollars per carat.

Emeralds cut and in matrix, tsavorite cut and in matrix, peridot and diopside and corundum, topaz and diamonds scintillating.

Take corundum that's too light or too orange or too purple or whatever, add controlled heat, and you end up with better color in your gems.

Only a few common minerals can resist an acidic environment: quartz, corundum, a few sulphates.

The trade kit dangled loose from his sash: a heat-and-pressure gadget, a pouch of corundum, small phials of additives for color.

The trade kit was a pouch of corundum, A1203, several phials of additives, and the heat-and-pressure gadget.

Svetz poured corundum into the chamber, added a dash of chromic oxide, and used the plunger.

But happiness glowed behind her homely face, and it made her almost passable, as she clutched the corundum stones.

Then he walked into the extension cage, leaving a trail of colored corundum beads behind him.

He had stored up several months' worth of rut in durance vile (mining corundum for emeralds and rubies that he would never see) after having been nipped up at Jorinne's orbiting space station.

He had not cared to use the high causey of corundum that spanned the fen, and had threaded his way with much peril from isle to sedgy isle that shuddered gelatinously beneath him.

Mineral occlusions were now strings and veins of beryl, shading here and there into lumps of raw emerald big as Investors' heads, crisscrossed with nets of red corundum and purple garnet.

Once the rough slabs were evened out, cut to straight edges and flat surfaces, they moved down a roller path where teams scoured and polished them with coarse corundum abrasives on rotating heads.