/mang"geuh nees', -neez'/ , n. Chem.
a hard, brittle, grayish-white, metallic element, an oxide of which, MnO 2 (manganese dioxide) , is a valuable oxidizing agent: used chiefly as an alloying agent in steel to give it toughness. Symbol: Mn; at. wt.: 54.938; at. no.: 25; sp. gr.: 7.2 at 20°C.
[ 1670-80; manganèse manganese, alter. of ML magnesia MAGNESIA ]