Magnesium (pronounced /mæɡˈniːziəm/, mag-NEE-zee-əm) is a chemical element with the symbol Mg, atomic number 12 and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the earth's crust by mass, although ninth in the Universe as a whole. This preponderance of magnesium is related to the fact that it is easily built up in supernova stars from a sequential addition of three helium nuclei to carbon (which in turn is made from three helium nuclei). Magnesium constitutes about 2% of the Earth's crust by mass, which makes it the eighth most abundant element in the crust. Magnesium ion's high solubility in water helps ensure that it is the third most abundant element dissolved in seawater.

Magnesium is the 11th most abundant element by mass in the human body; its ions are essential to all living cells, where they play a major role in manipulating important biological polyphosphate compounds like ATP, DNA, and RNA. Hundreds of enzymes thus require magnesium ions in order to function. Magnesium is also the metallic ion at the center of chlorophyll, and is thus a common additive to fertilizers. Magnesium compounds are used medicinally as common laxatives, antacids (i.e., milk of magnesia), and in a number of situations where stabilization of abnormal nerve excitation and blood vessel spasm is required (i.e., to treat eclampsia). Magnesium ions are sour to the taste, and in low concentrations help to impart a natural tartness to fresh mineral waters.

The free element (metal) is not found naturally on Earth, since it is highly reactive (though once produced, is coated in a thin layer of oxide—see passivation—which partly masks this reactivity). The free metal burns with a characteristic brilliant white light, making it a useful ingredient in flares. The metal is now mainly obtained by electrolysis of magnesium salts obtained from brine. Commercially, the chief use for the metal is as an alloying agent to make aluminium-magnesium alloys, sometimes called "magnalium" or "magnelium". Since magnesium is less dense than aluminium, these alloys are prized for their relative lightness and strength.

• Deficiency and Toxicity@ (14)

See also:

• Science: Chemistry: Elements: Magnesium (10)

• Ohio State University Extension Fact Sheet: Magnesium
  ohioline.osu.edu
  This fact sheet explains the role of magnesium in the body, and which foods we should eat to get an adequate daily amount.
• Slow-Mag Magnesium Supplements
  slowmag.com
  This magnesium chloride product helps protect against magnesium deficiency.
• MedlinePlus: Magnesium in Diet
  nlm.nih.gov
  Description of mineral including major functions, food sources, and deficiency signs.