Bismite is a bismuth oxide mineral, bismuth trioxide or Bi2O3. It is a monoclinic mineral, but the typical form of occurrence is massive and clay-like with no macroscopic crystals. The color varies from green to yellow. It has a Mohs hardness of 4 to 5 and a specific gravity of 8.5 to 9.5, quite high for a nonmetallic mineral.

Bismite is a secondary oxidation zone mineral which forms from primary bismuth minerals.

It was first described from Goldfield, Nevada in 1868, and later from the Schneeberg District, Ore Mountains, Saxony, Germany.