Very bright, low density metal which slowly becomes dull on exposure to the atmosphere m.p. 648.8 ºC; 1199.8 ºF b.p. 1090 ºC; 1994 ºF density 1.738 g/cc; 108.5 pounds/cubic foot	memory peg
	1808 Sir Humphry Davy, England
	Μαγνησια (Magnisia), region in Thessaly (Greece) named Magnesium alba since antiquity, named Magnium by the discoverer

Magnesium has long been known. Alchemists used magnesia alba, white magnesia or also known as mild magnesian earth (hydrated magnesium carbonate, 4MgCO₃.Mg(OH)₂.5H₂O was magnesia alba levis, and MgCO₃.Mg(OH)₂.4H₂O was magnesia alba ponderosa). The term magnesia alba was used in contrast with magnesia nigra, black manganese oxyde (MnO₂).

In the drought of 1618 Henry Wicker noted thirsty cattle would not drink from a water hole on the commons at Epsom, Surrey. The salts found in water of these mineral sources were described in 1695 in an article by Nehemia Grew. The medicinal properties of this salt attracted some attention. Epsom's salts were distinguished from other salts and became a fashionable spa for their healing effects on sores. The water contained Magnesium sulfate (MgSO₄.7H₂O), which was called "Epsom salts" in England (epsomite) and "salt anglicum" or bitter salt elsewhere.

In 1707 M.B. Valentin prepared magnesia alba from the mother liquors obtained in the manufacture of nitre and in 1755 Joseph Black (1728-1799) of Edinburgh distinguished quicklime (calcium oxide, CaO) from magnesia alba (both substances were confounded until that time).

In 1808, Sir Humphry Davy (1778-1829) isolated the metal (not pure) and called it Magnium to avoid to avoid confusion with Manganese, the metal found in magnesia nigra (note):

Despite Davy's proposal, the term Magnesium persisted for refering to the element in the magnesia alba. In Russian and a few other Slavic languages the form Magnium (Магний) is in use.

• The Czech and Slovak names are derived from horky = bitter, after the compound bitter salt.

The names magnesia alba and magnesia nigra are derived from Magnesia, Μαγνησια, a prefecture in Thessaly (Greece), with the capital Volos) (see map to the left). Manganese and Magnesium were abundant in oxide and carbonate ores in this region, and they therefore became referred as Μαγνητις λιθος, or stones from Magnesia. The region also contained large amounts of iron oxides (magnetite, or lodestone, for example) so that the ores were magnetized. That explains why magnesium as well as magnet (and magnetism) are derived from Magnesia, while magnesium is not magnetic.

The name Μαγνησια (Magnesia) derives from the Macedonian tribe name "Magnetes". The legendary Greek hero Μαγνης (Magnes) belived the protoplast of this tribe was the son of Eol and Enarete or Zeus and Thyia. The Magnetes have lived on Magnesia peninsula (Thessaly) and later colonized the Anatolia in Asia Minor.
Two towns were named after them Asia Minor: Magnesia ad Maeandrum near Ephesus (abandoned after the Roman times) and Magnesia ad Sipylum near Smyrna (nowadays Manisa).

Austrium

The name Austrium was given by Anton Rupprecht in 1792 to the impure Magnesium prepared by him. He honoured herewith his country Austria (note).

Crodonium

In 1819 Johann Bartholomäus Trommsdorf (1770-1837) in Erfurt reports that he has found a new metal in a salt on the bottom of a bottle of English sulphuric acid. He named it Crodonium, after the god Crodo, who was worshipped in ancient times in Thüringen (Erfurt is the capital of that region) (note). Shortly afterwards, Trommsdorf himself reported that Crodonia was not a new metal, but Magnesia (Magnesium oxide) with a small amount of Copper oxide (note).

• Mary Elvira Weeks, Discovery of the Elements, comp. rev. by Heny M. Leicester (Easton, Pa.: Journal of Chemical Education, 1968), pp. 495-502.
• Joseph Black (1728-1799), Experiments upon Magnesia Alba, Quick-Lime, and some other Alkaline Substances.
• Roland Mathieu, Magnetism of manganites, semiconductors and spin glasses. Dissertation Uppsala University, 2002 (PDF-file on-line).