A rare, dense, silvery-white metallic element with a very high melting point, extracted chiefly from molybdenite and used for electrical contacts, with tungsten for high-temperature thermocouples, and as a catalyst for refining hydrocarbon fuels. Atomic number 75; atomic weight 186.2; melting point 3,185°C; boiling point 5,596°C; specific gravity 20.8 (20°C); valence 1, 2, 3, 4, 5, 6, 7. See Periodic Table.