A silvery, soft, rare, ductile metallic element that occurs chiefly in columbite-tantalite and is used in steel alloys, arc welding, and superconductive materials. Atomic number 41; atomic weight 92.906; melting point 2,477°C; boiling point 4,744°C; specific gravity 8.57; valence 2, 3, 5. See Periodic Table.