Manganese (Mn) is a silvery-gray metallic transition metal of the 7^th group of the periodic table. It is hard and brittle. In the earth's crust, it occurs with a frequency of 1000 ppm (0.1%) and is therefore its 12^th most common element. It does not occur in its elemental form, but in the form of silicate-, carbonate- and above all as oxide compounds. The most important sources of manganese are rhodochrosite-braunite ores (MnCO₃ and MnO_1.7-2), heavily oxidized iron and silicate-rich sedimentary rocks, as well as manganese shale ores. A potentially important source of manganese are manganese nodules from the deep sea.

Pure manganese is only used to a limited extent. The majority (around 80-90% of the manganese extracted) is used as ferromanganese, spiegeleisen or silicon manganese in the steel industry. In steel, it has a deoxidizing and desulphurising effect and increases the solubility of nitrogen, which promotes the formation of austenite. It also increases the hardenability of steel.

In alloys with non-ferrous metals, such as copper and aluminium-manganese alloys, it increases strength, corrosion resistance and ductility. The copper-manganese-nickel alloy "Manganin" has a low electrical temperature coefficient, which is why it is widely used in electrical measuring devices.