It's Elemental

Although it is the eighth most abundant element in the universe and the seventh most abundant element in the earth's crust, magnesium is never found free in nature. Magnesium was first isolated by Sir Humphry Davy, an English chemist, through the electrolysis of a mixture of magnesium oxide (MgO) and mercuric oxide (HgO) in 1808. Today, magnesium can be extracted from the minerals dolomite (CaCO₃·MgCO₃) and carnallite (KCl·MgCl₂·6H₂O), but is most often obtained from seawater. Every cubic kilometer of seawater contains about 1.3 billion kilograms of magnesium (12 billion pounds per cubic mile).

Magnesium burns with a brilliant white light and is used in pyrotechnics, flares and photographic flashbulbs. Magnesium is the lightest metal that can be used to build things, although its use as a structural material is limited since it burns at relatively low temperatures. Magnesium is frequently alloyed with aluminum, which makes aluminum easier to roll, extrude and weld. Magnesium-aluminum alloys are used where strong, lightweight materials are required, such as in airplanes, missiles and rockets. Cameras, horseshoes, baseball catchers' masks and snowshoes are other items that are made from magnesium alloys.

Magnesium oxide (MgO), also known as magnesia, is the second most abundant compound in the earth's crust. Magnesium oxide is used in some antacids, in making crucibles and insulating materials, in refining some metals from their ores and in some types of cements. When combined with water (H₂O), magnesia forms magnesium hydroxide (Mg(OH)₂), better known as milk of magnesia, which is commonly used as an antacid and as a laxative.

Hydrated magnesium sulphate (MgSO₄·7H₂O), better known as Epsom salt, was discovered in 1618 by a farmer in Epsom, England, when his cows refused to drink the water from a certain mineral well. He tasted the water and found that it tasted very bitter. He also noticed that it helped heal scratches and rashes on his skin. Epsom salt is still used today to treat minor skin abrasions.

Other magnesium compounds include magnesium carbonate (MgCO₃) and magnesium fluoride (MgF₂). Magnesium carbonate is used to make some types of paints and inks and is added to table salt to prevent caking. A thin film of magnesium fluoride is applied to optical lenses to help reduce glare and reflections.