The Collaborative International Dictionary of English v.0.48:
Manganese \Man`ga*nese"\, n. [F. mangan[`e]se, It. manganese,
sasso magnesio; prob. corrupted from L. magnes, because of
its resemblance to the magnet. See Magnet, and cf.
An element obtained by reduction of its oxide, as a hard,
grayish white metal, fusible with difficulty (melting point
1244[deg] 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].
[1913 Webster +PJC]
Note: An alloy of manganese with iron (called ferromanganese)
is used to increase the density and hardness of steel.
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.