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 3½. 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,... Found on http://en.wikipedia.org/wiki/Russellite