Magnesium is the eighth most abundant element. Magnesium oxide, MgO, is the second most common compounds in the earth's crust, second only to silicon dioxide, or ordinary beach sand. In seawater, the principal magnesium compound is magnesium chloride, MgCl2. The chloride is obtained directly from seawater and is chiefly used in the electrolysis process to manufacture magnesium metal. When seawater is not conveniently available, magesium can be recovered from minerals such as dolomite (CaCO3.MgCO3) and carnallite (KCl.MgCl2.6H2O).

Discovered in 1775, Magnesium is a chemically active metal. Finely ground or powdered magnesium burns easily in air, producing a brilliant white light. Magnesium is an important alloying agent for improving the working characteristics of aluminum and zinc. It makes them easier to roll, extrude, weld and machine. Magnesium is also flammable at temperatures characteristic of burning gasoline and other petrochemicals, so its use as a structural metal is limited. Insoluble magnesium carbonate and magnesium sulfate, together with insoluble calcium compounds occur in "hard" water. These compounds are observed as scales in pipes and boilers. However, magnesium is an important catalyst in organic reactions.

Magnesium a metal that is essential to good health. A deficiency in man can have the same effect as alcoholism. Magnesium hydroxide, Mg(OH)2, is used in medicine as an antacid.

Other magnesium compounds include:

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