Magnesium, in common with other alkaline earth metals has a +2 oxidation number and a shiny, silvery-white colour. The British chemist Joseph Black (1728 - 1799) distinguished quicklime (calcium oxide, CaO) from magnesia alba in 1755. Humphry Davy isolated the metal, with some impurities in 1808 using electrolysis. He named the metal "magnium".
Alchemists used the metal magnesium in the form of ''magnesia alba'' (white magnesium), which was hydrated magnesium carbonate:
- 4MgCO3.Mg(OH)2.5H2O, magnesia alba levis.
- MgCO3.Mg(OH)2.4H2O, magnesia alba ponderosa.
Magnesium is used in flares, as it produces a brilliant white light when burnt in air.