Manganese

Manganese is a chemical element; it has symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. First isolated in the 1770s, manganese is a transition metal with many industrial alloy uses, particularly in stainless steels. It improves strength, workability, and resistance to wear. Manganese oxide is used as an oxidising agent, as a rubber additive, and in glass making, fertilizers, and ceramics. Manganese sulfate can be used as a fungicide.

Manganese is also an essential human dietary element, important in macronutrient metabolism, bone formation, and free radical defense systems. It is a critical component in dozens of proteins and enzymes. It is found mostly in the bones, but also the liver, kidneys, and brain. In the human brain, the manganese is bound to manganese metalloproteins, most notably glutamine synthetase in astrocytes.

Manganese is commonly found in laboratories in the form of the deep violet salt potassium permanganate where it is used as an oxidizer. Potassium permanganate is also used as a biocide in water treatment.

It occurs at the active sites in some enzymes. Of particular interest is the use of a Mn–O cluster, the oxygen-evolving complex, in the production of oxygen by plants.

Manganese is a silvery-gray metal that resembles iron. It is hard and very brittle, difficult to melt, but oxidizes easily. Manganese and its common ions are paramagnetic. Manganese tarnishes slowly in air and oxidizes ("rusts") like iron in water containing dissolved oxygen.

Naturally occurring manganese is composed of one stable isotope, ⁵⁵Mn. Several radioisotopes have been isolated and described, ranging from ⁴⁶Mn to ⁷²Mn. The most stable are ⁵³Mn with a half-life of 3.7 million years, ⁵⁴Mn with a half-life of 312.08 days, and ⁵²Mn with a half-life of 5.591 days. All of the remaining radioactive isotopes have half-lives of less than three hours, and the majority of less than one minute. The primary decay mode in isotopes lighter than the most abundant stable isotope, ⁵⁵Mn, is electron capture, and the primary mode in heavier isotopes is beta decay. Manganese also has three meta states.

Manganese is part of the iron group of elements, which are thought to be synthesized in massive stars shortly before the supernova explosion. ⁵³Mn decays to ⁵³Cr with a half-life of 3.7 million years. Because of its short half-life, ⁵³Mn is relatively rare; it is produced by the impact of cosmic rays on iron.

Chromium and manganese are found together sufficiently for measurement of both to find application in isotope geology, and the Mn/Cr ratios here for dating the early Solar System. Mn–Cr isotopic ratios reinforce the evidence from ²⁶Al and ¹⁰⁷Pd for the early history of the Solar System. Variations in ⁵³Cr/⁵²Cr and Mn/Cr ratios from several meteorites suggest a non-zero initial ⁵³Mn/⁵⁵Mn ratio, which indicate that Cr isotopic composition variations must result from in situ decay of ⁵³Mn in differentiated planetary bodies. Hence, ⁵³Mn provides additional evidence for nucleosynthetic processes immediately before the coalescence of the Solar System.