What is "al2o3"

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.

Alumina \A*lu"mi*na\, n. [L. alumen, aluminis. See Alum.] (Chem.) One of the earths, consisting of two parts of aluminium and three of oxygen, Al2O3.

Note: It is the oxide of the metal aluminium, the base of aluminous salts, a constituent of a large part of the earthy siliceous minerals, as the feldspars, micas, scapolites, etc., and the characterizing ingredient of common clay, in which it exists as an impure silicate with water, resulting from the decomposition of other aluminous minerals. In its natural state, it is the mineral corundum.

Sesquioxide \Ses`qui*ox"ide\, n. [Sesqui- + oxide.] (Chem.) An oxide containing three atoms of oxygen with two atoms (or radicals) of some other substance; thus, alumina, Al2O3 is a sesquioxide.

Sapphire \Sap"phire\ (? or ?; 277), n. [OE. saphir, F. saphir, L. sapphirus, Gr. ?, of Oriental origin; cf. Heb. sapp[=i]r.]

1. (Min.) Native alumina or aluminium sesquioxide, Al2O3; corundum; esp., the blue transparent variety of corundum, highly prized as a gem.

   Of rubies, sapphires, and of pearl['e]s white.
   --Chaucer.

   Note: Sapphire occurs in hexagonal crystals and also in granular and massive forms. The name sapphire is usually restricted to the blue crystals, while the bright red crystals are called Oriental rubies (see under Ruby), the amethystine variety Oriental amethyst (see under Amethyst), and the dull massive varieties corundum (a name which is also used as a general term to include all varieties). See Corundum.

2. The color of the gem; bright blue.

3. (Zo["o]l.) Any humming bird of the genus Hylocharis, native of South America. The throat and breast are usually bright blue.

   Star sapphire, or Asteriated sapphire (Min.), a kind of sapphire which exhibits asterism.