Manganese

Manganese was isolated in 1774 by Johan Gottlieb Gahn, after Carl Wilhelm Scheele had shown that its ore, pyrolusite, contained a new metal. Its name descends, like that of magnesium, from Magnesia in Greece; the black ore was called magnesia nigra to distinguish it from the white magnesia alba, and manganese is a corruption of that word. Manganese is a hard, brittle grey metal, essential in steelmaking for removing oxygen and sulfur and for hardening the alloy. Among the more abundant elements of the crust, manganese is also central to dry-cell batteries and is an essential trace nutrient in living things, forming part of the enzymes that protect cells against oxidative damage.

Manganese occurs on the deep ocean floor in vast fields of potato-sized manganese nodules, rich also in nickel, copper and cobalt, a resource that has made seabed mining one of the more contested modern environmental questions, since dredging the nodules risks disturbing ecosystems scientists have barely begun to catalogue. Gahn achieved his isolation by heating powdered pyrolusite with oil and carbon in a crucible, a simple reduction that nonetheless required Scheele's prior chemical analysis to know a genuine new metal, and not merely a curious black earth, was waiting to be freed.

Manganese compounds have served human craft since prehistory: manganese dioxide gave the deep blacks and browns of Palaeolithic cave paintings, and the same substance, called glassmakers' soap, was added to molten glass from Roman times to cancel the green tint of iron and produce clear glass, or in excess to colour it purple. The element's name is entangled with magnesium and magnet through their common origin in the mineral wealth of Magnesia, a confusion early chemists worked to separate. Manganese has no planetary or alchemical station of its own, but as a pigment and a glassmaker's reagent its ores were worked and valued long before the metal was named.

Archaeologists have recovered manganese oxide crayons, shaped and worn from use, at Palaeolithic sites including those near Lascaux, direct physical evidence that prehistoric artists deliberately sought out and prepared the mineral for its pigment. Pliny the Elder described the glass-clarifying property of manganese ore in the first century, a practical knowledge that long predated any understanding of why it worked. The element also has a harsher occupational history: miners and smelters exposed for years to manganese dust can develop manganism, a Parkinson's-like neurological disorder first clinically described in 1837 by James Couper among Scottish workers grinding manganese ore at a Glasgow bleach works, with the much cited Chilean cases following more than a century later.