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Magnesium (Mg)

Magnesium (symbol Mg) is the chemical element with atomic number 12: an alkaline earth metal, solid at 0 °C, with an atomic mass of 24.305 u. Discovered in 1755 (Joseph Black).

Magnesium is a very light metal, about a third lighter than aluminium. It burns with a blinding white light that early photographers once used as a flash. At the center of every chlorophyll molecule sits a magnesium atom: without it, no photosynthesis. Our bodies need it for hundreds of reactions.

Key facts

Atomic number
12
Symbol
Mg
French name
Magnésium
Atomic mass
24.305 u
Molar mass
24.305 g/mol
Family
Alkaline earth metals
Position
period 3, group 2, s-block
State at 0 °C
Solid
Melting point
649.9 °C
Boiling point
1,089.9 °C
Density
1.74 g/cm³
Electronegativity (Pauling)
1.31
First ionization energy
738 kJ/mol
Atomic radius
150 pm
Electron configuration
[Ne] 3s²
Abundance in Earth's crust
23,300 ppm (7th most abundant element)
Indicative price
2 $/kg (order of magnitude)
Radioactive
no
Discovery
1755, Joseph Black

Origin of the name

From Magnesia, a district of Thessaly in Greece.

What does magnesium look like?

A light, silvery-gray metal that dulls slightly in air as it forms a thin protective oxide layer.

Where is magnesium found?

About 2.3% of Earth's crust, and very abundant in the mantle as olivine. Seawater contains 1.3 g per liter, making it an almost inexhaustible source. The human body contains about 25 g, more than half of it in the bones.

Natural sources

  • Dolomite
  • Magnesite
  • Carnallite
  • Olivine
  • Brucite

How is magnesium produced?

About 1 million tonnes of metal a year, mostly made in China by the Pidgeon process, which reduces calcined dolomite with ferrosilicon at around 1,200 °C. Elsewhere it is obtained by electrolysis of molten magnesium chloride, sourced notably from brines or seawater.

Top producers

  • China
  • Russia
  • Israel
  • Kazakhstan

What is magnesium used for?

  • Additive in aluminium alloys (cans, car bodies).
  • Ultralight alloys for cars, aircraft and laptops.
  • Removing sulfur from steel.
  • Fireworks and signal flares.
  • Refractory furnace bricks (magnesia).
  • Dietary supplements and laxatives.

In everyday life

  • A soda can (aluminium-magnesium alloy)
  • The white sparks of fireworks
  • The chassis of some laptops and cameras
  • Epsom bath salts

Role in living things

Essential: it takes part in more than 300 enzymes, notably those that use ATP, the cell's “energy currency.” It plays a role in muscle contraction and heart rhythm. In plants, it sits at the center of chlorophyll.

Hazards of magnesium

As shavings or powder, it ignites easily and burns at more than 3,000 °C. Water makes the fire worse by releasing hydrogen, and it even keeps burning in carbon dioxide: it must be smothered with dry sand. Its salts are of low toxicity, but laxative at high doses.

Cosmic origin

  • Supernovae: Forged in the cores of massive stars, then scattered when they explode.

History of magnesium

The name comes from Magnesia, a region of Greece rich in minerals. In 1755, the Scot Joseph Black recognized magnesia as a substance distinct from lime. Humphry Davy isolated impure magnesium by electrolysis in 1808, and Antoine Bussy produced the metal in quantity in 1831.

Did you know?

  • In the 1955 Le Mans disaster, the magnesium-alloy body of the crashed Mercedes burned for a long time, and the firefighters' water only fed the flames.
  • Epsom salt (magnesium sulfate) is named after a bitter spring in Epsom, England, discovered in the 17th century.
  • A strip of burning magnesium gives off light so intense that you shouldn't look straight at it.

Isotopes of magnesium

Three stable isotopes. An excess of magnesium-26 in some meteorites is the fingerprint of radioactive aluminium-26 present at the birth of the Solar System.

  • magnesium-24: 78.99% of natural magnesium, stable
  • magnesium-25: 10% of natural magnesium, stable. Stable tracer for studying how the body absorbs magnesium.
  • magnesium-26: 11.01% of natural magnesium, stable. A decay product of aluminium-26, it dates the formation of the Solar System's first solids.
  • magnesium-28: radioactive, half-life 20.9 h. Radioactive tracer in biology and soil research.

Common compounds

Chlorophyll a (C₅₅H₇₂MgN₄O₅)

Related elements

Same family (alkaline earth metals): Beryllium (Be), Calcium (Ca), Strontium (Sr), Barium (Ba), Radium (Ra).

Same column (group 2): Beryllium (Be), Calcium (Ca), Strontium (Sr), Barium (Ba), Radium (Ra).