Russellite is a bismuth tungstate mineral with the chemical formula Bi2WO6. It crystallizes in the orthorhombic crystal system. Russellite is yellow or yellow-green in color, with a Mohs hardness of 3 1/2. Russellite is named for the mineralogist Sir Arthur Russell, and the type locality is the Castle-an-Dinas Mine, near St Columb Major in Cornwall, where it was found in 1938 in wolframite. It occurs as a secondary alteration of other bismuth bearing minerals in tin−tungsten hydrothermal ore deposits, pegmatites and greisens. It typically occurs associated with native bismuth, bismuthinite, bismite, wolframite, ferberite, scheelite, ferritungstite, anthoinite, mpororoite, koechlinite, cassiterite, topaz, muscovite, tourmaline and quartz.