Magnesium: The Light Metal in Stars, Seas and Our Cells

What exactly is magnesium?

Magnesium is listed as Mg with atomic number 12 ². Its atomic mass is 24.305 ². At room temperature it is a solid ². It belongs to the alkaline earth metals, the group 2 metals of the periodic table ¹².

In plain terms, it is a gray metal that weighs little for its size ¹. Its density is 1.74 g per cubic centimetre ². That is roughly two thirds the weight of the same volume of aluminium ¹. It melts at 649.9 C and boils at 1,089.9 C ². It reacts easily with other substances ¹. In air, a thin skin of oxide forms on the surface and slows further change ¹.

It was isolated in 1808 ². In nature it is almost never found alone ¹. It is usually joined with other elements and carries a +2 charge ¹.

Where is magnesium found and what do we use it for?

Magnesium is widespread. It ranks eighth among elements in Earth's crust ¹. For the whole Earth, it ranks fourth, after iron, oxygen and silicon ¹. It makes up 13% of the planet's mass and much of the mantle, the thick layer below the crust ¹. In seawater, it ranks third among dissolved elements, after sodium and chlorine ¹.

Industry gets the metal largely by using electricity to split magnesium salts taken from salty water ¹. Because it weighs less than aluminium, it is added to aluminium to make strong and light mixes for parts and products ¹. In 2013, use of such mixes was under one million tonnes per year, far below 50 million tonnes for aluminium mixes ¹. Wider use was held back because these mixes can rust in a chemical sense, change shape slowly when hot, and catch fire ¹.

Magnesium compounds also have medical uses ¹. Common laxatives and antacids include milk of magnesia ¹. This article does not give health advice, so readers should ask a clinician or official source about any treatment ¹.

What is surprising about magnesium?

Its story starts in space. Big aging stars build it when carbon gains three helium cores in steps ¹. When those stars burst as supernovas, much of it spreads into space ¹. That scattered material can later become part of new stars and planets ¹.

It is also striking to watch. Once lit, the pure metal gives off an intense white glow ¹. Large blocks are hard to light, while powder and thin strips light more readily ¹. In people, it ranks eleventh by mass ¹. Yet it is needed in every cell and helps about 300 enzymes do their jobs ¹. Its charged particles work with energy carriers and genetic material, including ATP, DNA and RNA, and hundreds of enzymes depend on them ¹.