What is "magnesium oxide"

magnesium oxide \magnesium oxide\ n. (Chem.) Magnesia.

n. (context inorganic compound English) A white powder (MgO) with a high melting point; it occurs naturally as periclase, an ore of magnesium.

n. a white solid mineral that occurs naturally as periclase; a source of magnesium [syn: periclase, magnesia]

Magnesium oxide ( Mg O), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of and consists of a lattice of Mg ions and O ions held together by ionic bonding. Magnesium hydroxide forms in the presence of water (MgO + HO → Mg(OH)), but it can be reversed by heating it to separate moisture.

Magnesium oxide was historically known as magnesia alba (literally, the white mineral from magnesia - other sources give magnesia alba as MgCO), to differentiate it from magnesia negra, a black mineral containing what is now known as manganese.

While "magnesium oxide" normally refers to MgO, magnesium peroxide MgO is also known as a compound. According to evolutionary crystal structure prediction, MgO is thermodynamically stable at pressures above 116 GPa (gigapascals), and a totally new semiconducting suboxide MgO is thermodynamically stable above 500 GPa. Because of its stability, MgO is used as a model system for investigating vibrational properties of crystals.