manganese - a hard brittle gray polyvalent metallic element that resembles iron but is not magnetic; used in making steel; occurs in many mineralsmetal, metallic element - any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc. hausmannite - a mineral consisting of manganese tetroxide; a source of manganese manganite - a black mineral consisting of basic manganese oxide; a source of manganese psilomelane - a mineral consisting of hydrated basic oxide of manganese and barium; a source of manganese pyrolusite - a mineral consisting of manganese dioxide; an important source of manganese rhodochrosite - a mineral consisting of manganese carbonate; a source of manganese |