Magnesia

Magnesia most often refers to magnesium oxide, MgO, an inorganic compound produced by calcining magnesium carbonate minerals such as magnesite (MgCO3) or by heating magnesium hydroxide (Mg(OH)2). In pure form it is a white, odorless, highly refractory solid with a melting point above 2800 °C and a low solubility in water. As a basic oxide, MgO readily reacts with acids to form magnesium salts and, on contact with water, slowly hydrates to form magnesium hydroxide.

Natural magnesia occurs in minerals such as periclase (MgO) and magnesite (MgCO3); the hydrous mineral brucite (Mg(OH)2) is also related. The material is produced commercially by calcining magnesite or brucite or by hydration of magnesium salts.

Applications include use as a refractory material for furnace linings and crucibles, as a component of specialized cements and concretes, and as a protecting agent in metallurgical processes. It is also used as a filler and flame retardant in ceramics, plastics, and rubber. In agriculture, magnesium oxide and magnesium carbonate are used to correct magnesium-deficient soils and as a dietary supplement in some animal feeds. In medicine, magnesium oxide and magnesium hydroxide are used as antacids; magnesium hydroxide is also widely used as a laxative known as milk of magnesia.

Safety considerations: when handled as a powder, it can irritate the respiratory tract; proper dust control is recommended. It is relatively low in toxicity but excessive ingestion or inhalation should be avoided.