Magnesium oxide, powder, 99.9+%,

Magnesium oxide (MgO), or magnesia, is a white hydroscopic solid mineral that occurs naturally as periclase and is a source of magnesium. Magnesium oxide was historically known as magnesia alba, to differentiate it from magnesia negra, a black mineral containing what is now known as manganese. MgO is one of the raw materials for making Portland cement in dry plants. If too much MgO is added, the cement may become expansive. MgO is a relatively poor desiccant, but because it neutralizes sulfur oxide acids created by oxidation of Kraft-processed papers, it is used by many libraries for preserving books. In medicine, magnesium oxide is used for relief of heartburn and sore stomach, as an antacid, magnesium supplement, and as a short-term laxative. It is also used to improve symptoms of indigestion. Side effects of magnesium oxide may include nausea and cramping. In quantities sufficient to obtain a laxative effect, side effects of long-term use include enteroliths resulting in bowel obstruction. MgO is used as an insulator in industrial cables, as a basic refractory material for crucibles and as a principal fireproofing ingredient in construction materials. As a construction material, magnesium oxide wallboards have several attractive characteristics: fire resistance, moisture resistance, mold and mildew resistance, and strength. It is used as a reference white color in colometry, owing to its good diffusing and reflectivity properties. It may be smoked onto the surface of an opaque material to form an integrating sphere. MgO is also used as a protective coating in plasma displays.