from The American Heritage® Dictionary of the English Language, 4th Edition
- n. An extremely hard mineral, aluminum oxide, Al2O3, sometimes containing iron, magnesia, or silica, that occurs in gem varieties such as ruby and sapphire and in a common black, brown, or blue form used chiefly in abrasives.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. An extremely hard mineral, a form of aluminum oxide with the chemical formula Al2O3, that occurs in the form of the gemstones sapphire and ruby; it is used as an abrasive.
from the GNU version of the Collaborative International Dictionary of English
- n. 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.
from The Century Dictionary and Cyclopedia
- n. Alumina, or the oxid of the metal aluminium, as found native in a crystalline state.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. very hard mineral used as an abrasive
Aluminum oxide, when it occurs in crystals rather than on pans, makes up the abrasive called corundum, and is also the principal material of rubies and sapphires the gem colors come from chromium and titanium impurities.
The relatively pure crystals are called corundum, while emery is
It should be said first that the only true scientific or synthetic stones on the market are those having the composition and properties of corundum, that is to say, the ruby and the several color varieties of sapphire, as blue, pink, yellow, and white.
The oriental jacinth, or hyacinth, is a brown-red corundum, which is more stable than the ordinary hyacinth, this latter being a form of zircon; it changes colour on exposure to light, which colour is not restored by subsequent retention in darkness.
The cutting and polishing of the stones is done, as at home, with metal discs and emery or comminuted corundum, which is said to be found in large quantities in the neighbourhood of Canton.
The polishing of stones, whether cabochon or facetted, is accomplished by the use of very finely powdered abrasives such as corundum powder, tripoli, pumice, putty powder, etc.
Herein also is the kind of corundum known as emery, and esteemed for its polishing properties.
I am harder than a diamond sword sunk in a corundum anvil.
Minnesota Mining & Manufacturing Co. was formed in 1902 to mine corundum.
In crystal form, aluminum oxide is called corundum, sapphire or ruby (depending on the color), and it is among the hardest substances known.