Magnesium, not to be confused with manganese, is a light weight, brittle, shiny gray, and highly flammable metal that occurs naturally only in combination with other elements. It is the fourth most abundant element in the earth (after iron, oxygen and silicon), the eighth most abundant element in the earth's crust, and the fifth most abundant element dissolved in seawater.
Magnesium is essential to life. It is also the eleventh most abundant element by mass in the human body and is essential to all cells and approximately three hundred enzymes. Plants require magnesium to synthesize chlorophyll, which essential for photosynthesis. Magnesium compounds are used medicinally including as laxatives, antacids and stabilizers for abnormal nerve excitation and blood vessel spasms. Magnesium compounds and alloys are also used in large volumes in a wide range of industrial applications.