a white, extremely dense, brittle, corrosion-resistant chemical element, one of the platinum metals: alloys of iridium are used in electrodes, pen points, crucibles, etc.: symbol, Ir; at. no., 77
See iridium in American Heritage Dictionary 4
(ĭ-rĭdˈē-əm)
noun Symbol Ir
A very 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 192.2; melting point 2,446°C; boiling point 4,428°C; specific gravity 22.562 (at 20°C); valence 2, 3, 4, 6. See Table at element.