Manganese

n.
  1. An element obtained by reduction of its oxide, as a hard, grayish white metal, fusible with difficulty (melting point 1244° C), but easily oxidized. Its ores occur abundantly in nature as the minerals pyrolusite, manganite, etc. Symbol Mn. Atomic number 25; Atomic weight 54.938 [C=12.011].
    2. Black oxide of manganese, Manganese dioxide or Manganese peroxide, or Black manganese (Chem.),
    a heavy black powder MnO2, occurring native as the mineral pyrolusite, and valuable as a strong oxidizer; -- called also familiarly manganese. It colors glass violet, and is used as a decolorizer to remove the green tint of impure glass.