A very dense, hard, and brittle, exceptionally corrosion-resistant, whitish-yellow metallic element occurring in platinum ores and used principally to harden platinum and in high-temperature materials, electrical contacts, and wear-resistant bearings. Atomic number 77; atomic weight 192.22; melting point 2,446°C; boiling point 4,428°C; specific gravity 22.562 (at 20°C); valence 2, 3, 4, 6. See Periodic Table.