Manganese

Category: transition metal Atomic number: 25 Colour: silvery Melting point: 1,246°C (2,275°F) Boiling point: 2,061°C (3,742°F) First identified: 1774

The famous cave paintings of Lascaux, in France, demonstrate one of humanity’s first uses of a manganese compound: the black ore, manganese dioxide (or pyrolusite), makes a good black paint. Another compound, magnesium oxide, was used in Ancient Egypt to remove the green tint of glass (it was known as sapo vitri, meaning ‘glass soap’).

In its elemental form, manganese is a brittle, hard, silvery metal. About 1 per cent of it is used in the ‘Bessemer process’ method of steelmaking – it converts iron sulphide to manganese sulphide in the alloy – the latter has a much higher melting point. If you increase the proportion of manganese to about 13 per cent, you get ‘manganese steel’, which is extremely strong and is used in railway tracks, safes and the bars of prison cells. It is also alloyed with aluminium in drinks cans to lessen the risk of corrosion.

In the early eighteenth century it was assumed that manganese contained iron, but after a Berlin glassmaker demonstrated this must be untrue, various chemists attempted to isolate it before Johan Gottlieb Gahn’s successful 1774 attempt in Sweden. (Gahn may actually have been beaten to the post by a few years by a Viennese student, who apparently produced the metal but failed to publicize his findings.)

Rolling on the Ocean Floor

Did you know that there are millions of nodules containing a high proportion of manganese littered on the ocean floor? In some places, they cover as much as two-thirds of the seabed: the actions of certain sea creatures seem to prevent them from being buried in sediment. There are various theories about the formation of these nodules, but scientists agree that they have taken millions of years to ‘grow’. There has been a lot of interest in them from mining companies, since they could theoretically be harvested from the ocean, but this hasn’t happened, due to the high costs of doing so, and increasing concern about the potential environmental impact.

The name can be confusing. Both magnesium and manganese were named after Magnesia in north Greece (where lapis magnis or magnetic lodestones were first discovered). At one point, magnesium was known as white magnesia, while manganese was called black magnesia. This confusion was not cleared up until after Gahn’s breakthrough.

Manganese is the second most abundant transition metal after iron and appears in hundreds of minerals. It also plays a crucial role in photosynthesis and the development of certain enzymes: we consume trace amounts from foods like nuts, bran, wholegrain cereals, parsley and – most importantly from a British point of view – a nice cup of tea.