A rare, whitish-yellow element that is the most corrosion-resistant metal known. It is very dense, hard, and brittle, and is is used to make hard alloys of platinum for jewelry, pen points, and electrical contacts. Atomic number 77; atomic weight 192.2; melting point 2,410°C; boiling point 4,130°C; specific gravity 22.42 (at 17°C); valence 3, 4. See Periodic Table.