A-lū'mi-na or Ăl'ū-mīne, n.

n. [Fr. alumine, Sp. alumina, N. Lat. alumina.] (Min.) One of the earths, consisting of two parts of aluminum and three of oxygen. Dana.

☞ It is the oxide of the metal aluminum, the base of aluminous salts, a constituent of a large part of the earthy silicious minerals, as the feldspars, micas, scapolites, &c., 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 a pure, natural state, it is the mineral sapphire.