Image by Greg Robson
Elemental magnesium is a fairly strong, silvery-white, light-weight metal. Because it reacts with air, water and acids it’s never found naturally in a pure metal form but magnesium ions do dissolve easily and are the third most common element in seawater. You can sometimes taste magnesium, when it gives a tart taste to some mineral water!
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Magnesium metal is very impressive if you can get it to burn – it has a brilliant white flame. This flame is so bright that it has been used in fireworks, in marine flares (to send signals across large distances at sea) and in the flashes of Victorian cameras! Once lit, Magnesium will keep burning even in carbon dioxide or under water – which is why it was used in Word War II to firebomb enemy cities.
The most common use of magnesium is as a structural metal, usually when combined with aluminium to form a strong light-weight alloy. This alloy is used in making drinks cans and for building racing cars which need to be very light in order to go faster.
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Certain compounds of magnesium are also useful. In 1618, an English farmer from Epsom was very puzzled when his cows refused to drink water from a particular well. He noticed that though the water tasted quite bitter, it seemed able to heal scratches and rashes! He had discovered Epsom salts – which turned out to be the compound magnesium sulphate. Another medical use is in ‘milk of magnesia’ which is made from magnesium hydroxide particles suspended in water. Milk of magnesia is used as an antacid (to relieve heartburn) and is also a mild laxative (it helps constipated people to poo!).
Magnesium is vital to life on earth. Plants use a chemical called chlorophyll to make energy from sunlight, and in each chlorophyll molecule there is a magnesium ion.