The Swedish chemist Johan Gottlieb Gahn discovered the hard but brittle metallic element manganese (symbol Mn) in 1774. However, another Swedish chemist, Carl Wilhelm Scheele, proposed the existence of such an element prior to its discovery. Gahn isolated the element from the mineral pyrolusite. Pyrolusite has magnetic properties and the element’s name comes from the Latin word for magnet – “magnes”.
With an atomic number of 25 manganese takes its place in period 4, group 7 and the d-block of the periodic table. The metal melts at 1246°C (1519 K, 2275°F) and boils at 2061°C (2334 K, 3742°F). It has an atomic weight of 54.938045, a density of 7.3 grams per cubic centimeter and an ionization energy of 7.434 eV.
Although the metal is too brittle for structural use on its own, alloyed to iron manganese produces a steel with improved rolling and forging qualities, strength, toughness, stiffness, wear resistance, hardness and hardening ability. It also helps remove sulphur and oxygen contaminants from molten steel. The iron and steel industry uses about 90% of the world’s supply of manganese. The glass industry also uses manganese as it removes the green coloration caused by iron contaminants, as well as imparting an amethyst color to glass.
Th mineral pyrolusite provides much of the supply of manganese. Other minerals including rhodochrosite also contain manganese. The element’s most common compound, manganese dioxide (MnO2), forms 0.14% of the earth’s crust. Naturally occurring manganese, consists of just one stable isotope – manganese-55
Nodules found on the floor of the ocean contain up to 24% manganese. The source of the manganese making up these nodules and their mode of formation is the subject of scientific investigation. The presence of bacteria within the nodules suggests a biogenic origin. The nodules may provide an economically viable source of manganese in the future.
Manganese is a biologically essential trace element. Manganese deficiency causes infertility in mammals. The element is important in forming a number of enzymes. However, it is also toxic in high levels and manganese dust or fumes in the air must not exceed 5 milligrams per cubic meter.
There are for different temperature dependant allotropes of manganese designated alpha, beta, gamma and delta. The transformations occur at 700°C (973K, 1292°F), 1088°C (1361K, 1990°F) and 1139°C (1412K, 2082°F).
Materials Handbook: A Concise Desktop Reference – by François Cardarelli, Edition 2, Pub. 2008
Los Alamos National Laboratory Chemistry Division
Jefferson Laboratories Science Education website