Magnesium is named from a district in Thessaly, Magnesia, and was recognized as an element in 1755 and isolated in 1808. Magnesium is the eighth most abundant element in the earth's crust. It does not occur uncombined, but is found in large deposits in the form of magnesite, dolomite and other minerals and is principally obtained in the U.S. by electrolysis of fused magnesium chloride. Magnesium is a light, silvery-white, fairly tough metal that readily ignites and burns in air with a dazzling white flame. It is used in flash photography, flares, pyrotechnics and incendiary bombs. It is also used in alloys for airplane and missile construction. The hydroxide (milk of magnesia), chloride, sulfate (Epsom salts) and citrates are used medicinally. Magnesium is an important element in both plant and animal life.