Magnesium

In 1618, an English farmer named Henry Wicker noticed that his cows wouldn’t drink from a certain pool of water on his farm in Epsom, England. This was puzzling in part because England was suffering from a drought, so Wicker’s cows were thirsty! Although the water tasted bitter, Wicker noticed that it was helpful in healing scratches and cuts, and also that it could be used as a laxative. By evaporating the water, Wicker produced a salt that became known as Epsom salt. Epsom salts are still used today as a laxative and as a remedy for joint and muscle pain.

Wicker wasn’t aware that his Epsom salts were actually magnesium sulfate. That’s because it wasn’t until 1755 that Scottish chemist Joseph Black figured out that magnesium was a distinct element. Black was the first to understand the difference between magnesia (magnesium oxide, MgO) and lime (calcium oxide, CaO)—realizing that magnesia contained a new element even though its properties are very similar to lime (look at how they're positioned on the periodic table!). Black is also known for discovering carbon dioxide and for developing the materials-science concepts of latent heat and specific heat.

In 1792, Austrian scientist Anton Rupprecht heated magnesia with charcoal to obtain an impure version of magnesium metal. In 1808, chemist Sir Humphrey Davy of England managed to isolate a tiny but pure sample of the metal by electrolysis of magnesium oxide (using an electrical current to separate the magnesium and oxygen). In 1831, French chemist Antoine Bussy finally isolated a substantial amount of magnesium by reacting magnesium chloride with potassium.

Davy thought the element should be called magnium, but in the end, it became known as magnesium. The name comes from a Greek word for an area in modern-day Turkey, Magnesia, where a magnesium compound had been found.

Magnesium metal is tough, lightweight, shiny, and silver in color, although it tarnishes when exposed to air. Magnesium is highly flammable. It has been used in warfare partly because once it catches fire, it is extremely difficult to put out. In fact, adding water only makes the fire worse! The only way to stop a magnesium fire is by covering it with sand.

The bright light magnesium emits as it burns is why magnesium powder was used to produce a camera flash, in the early days of photography.

Like aluminum, magnesium is both strong and lightweight, so it is often used as a structural metal. Alloyed with other elements, magnesium can make metals that are strong and resistant to corrosion. That’s why magnesium alloys are essential in aircraft, missiles, and cars. The alloys are also valuable for objects for which weight is a concern, such as laptops, power tools, and luggage, and even in sporting equipment like bicycles. It's used to manufacture other metals, like steel and titanium, too.

Because it burns brightly and readily in air, magnesium is used in flares and fireworks. It has also been used in bombs and other weapons.

In medicine, magnesium hydroxide (or milk of magnesia) is used as an antacid or laxative. Magnesium sulfate (Epsom salt) is used in baths to soothe sore muscles and treat topical skin irritations. In the past, magnesium bromide was prescribed as a sedative.

Magnesium compounds play important roles in diverse areas. For example, magnesium carbonate is used in everything from flooring to fireproofing, cosmetics, and toothpaste. Magnesium oxide is used in fertilizer and cement production, in wastewater treatment, and as an anticaking agent in canned food and frozen desserts.

The mineral magnesium silicate is known as meerschaum, which was once used in Turkey to make tobacco pipes. Later, in the 19th century, meerschaum pipes caught on in Europe, too. (Nicholas Cage fans will remember that a meerschaum pipe played a key role in the 2004 film National Treasure.)

In nature, you’ll find magnesium in three stable (non-radioactive) isotopes—magnesium-24, -25, and -26. Of these isotopes, magnesium-24 is by far the most common, with about 80 percent of natural magnesium occurring in this form. 

Scientists have discovered 19 radioactive magnesium isotopes, ranging from magnesium-19 to magnesium-40. The longest-lived of these isotopes, magnesium-28, has a half-life of around 20 hours, while the shortest-lived has a half-life of about 4 zeptoseconds. A zeptosecond is a trillionth of a billionth of a second, or about as long as it takes to drink a milkshake on a summer afternoon!

By mass, magnesium is the fourth most abundant element on Earth after iron, oxygen, and silicon. It’s the seventh most abundant in the earth’s crust. It is found in large deposits in the form of magnesite, dolomite, and other minerals.

In the United States, magnesium metal is principally obtained by electrolysis of magnesium chloride from brines, wells, and seawater. China produces around three quarters of the world’s annual magnesium output.

Many foods, including almonds, cashew nuts, parsnips, bran, and chocolate, are high in magnesium. (If you needed an excuse to eat chocolate, now you have one!) Although magnesium is a vital element for humans, magnesium deficiency is a rare condition because most people have a substantial amount of the element stored in their bones.