'iridium' definitions:

Definition of 'iridium'

From: WordNet
noun
A heavy brittle metallic element of the platinum group; used in alloys; occurs in natural alloys with platinum or osmium [syn: iridium, Ir, atomic number 77]

Definition of 'iridium'

From: GCIDE
  • iridium \i*rid"i*um\ ([-i]*r[i^]d"[i^]*[u^]m), n. [NL., fr. L. iris, iridis, the rainbow. So called from the iridescence of some of its solutions. See Iris.] (Chem.) A rare metallic element of atomic number 77, of the same group as platinum, which it much resembles, being silver-white and indifferent to most corrosive agents, but harder, more brittle, and with a higher melting temperature (2410[deg] C, versus platinum 1772[deg] C). With the exception of osmium, it is the heaviest substance known, its specific gravity being 22.4. Symbol Ir. Atomic weight 192.22. [1913 Webster +PJC]
  • Note: Iridium usually occurs as a native alloy with osmium (iridosmine or osmiridium), which may occur alone or with platinum. Iridium, as an alloy with platinum, is used in bushing the vents of heavy ordnance. It is also used for the points of gold pens, and in a finely powdered condition (iridium black), for painting porcelain black. [1913 Webster]

Definition of 'iridium'

From: Elements
  • Symbol: Ir
  • Atomic number: 77
  • Atomic weight: 192.217
  • Very hard and brittle, silvery metallic transition element. It has a yellowish cast to it. Salts of iridium are highly colored. It is the most corrosion resistant metal known, not attacked by any acid, but is attacked by molten salts. There are two natural isotopes of iridium, and 4 radioisotopes, the most stable being Ir-192 with a half-life of 73.83 days. Ir-192 decays into platinum, while the other radioisotopes decay into osmium. Iridium is used in high temperature apparatus, electrical contacts, and as a hardening agent for platinum. Discovered in 1803 by Smithson Tennant in England. The name comes from the Greek word iris, which means rainbow. Iridium metal is generally non-toxic due to its relative unreactivity, but iridium compounds should be considered highly toxic.