Iridium

Iridium is a <a href="/facts/Chemical_element/0jducgWD">chemical element</a>; it has <a href="/facts/Symbol_(chemistry)/2Fe1VAL0">symbol</a> Ir and <a href="/facts/Atomic_number/bgAr581S">atomic number</a> 77. A very hard, brittle, silvery-white <a href="/facts/Transition_metal/0slGWoLQ">transition metal</a> of the <a href="/facts/Platinum_group/pbDgst54">platinum group</a>, it is considered the second-densest naturally occurring metal (after <a href="/facts/Osmium/1TjXD69n">osmium</a>) with a density of 22.56 g/cm3 (0.815 lb/cu in) as defined by experimental <a href="/facts/X-ray_crystallography/WtI0F5DN">X-ray crystallography</a>. 191Ir and 193Ir are the only two naturally occurring <a href="/facts/Isotope/KD9B1y6o">isotopes</a> of iridium, as well as the only <a href="/facts/Stable_isotope/vgcdxgjA">stable isotopes</a>; the latter is the more abundant. It is one of the most <a href="/facts/Corrosion/lIC7H4we">corrosion</a>-resistant metals, even at temperatures as high as 2,000 °C (3,630 °F).
Iridium was discovered in 1803 in the acid-insoluble residues of <a href="/facts/Platinum/qJC6lQf7">platinum</a> ores by the English chemist <a href="/facts/Smithson_Tennant/l9PB5HCw">Smithson Tennant</a>. The name iridium, derived from the Greek word iris (rainbow), refers to the various colors of its compounds. Iridium is <a href="/facts/Abundance_of_elements_in_Earth%27s_crust/UDSVHH56">one of the rarest elements</a> in <a href="/facts/Crust_(geology)/FYG1kP4F">Earth's crust</a>, with an estimated annual production of only 6,800 kilograms (15,000 lb) in 2023.
The dominant uses of iridium are the metal itself and its alloys, as in high-performance <a href="/facts/Spark_plug/Y9lG10hg">spark plugs</a>, <a href="/facts/Crucible/o7WrIqhu">crucibles</a> for recrystallization of semiconductors at high temperatures, and electrodes for the production of chlorine in the <a href="/facts/Chloralkali_process/5aAamEP9">chloralkali process</a>. Important compounds of iridium are chlorides and iodides in industrial <a href="/facts/Catalysis/LPBS7TQC">catalysis</a>. Iridium is a component of some <a href="/facts/OLED/219L1aMJ">OLEDs</a>.
Iridium is found in <a href="/facts/Meteorite/NsmHlBlX">meteorites</a> in much higher abundance than in the Earth's crust. For this reason, the unusually high abundance of iridium in the clay layer at the <a href="/facts/Cretaceous%E2%80%93Paleogene_boundary/5056Agsq">Cretaceous–Paleogene boundary</a> gave rise to the <a href="/facts/Alvarez_hypothesis/ojlNS1Ik">Alvarez hypothesis</a> that the impact of a massive extraterrestrial object caused the <a href="/facts/Cretaceous%E2%80%93Paleogene_extinction_event/HNyDuEcx">extinction of non-avian dinosaurs and many other species 66 million years ago</a>, now known to be produced by the impact that formed the <a href="/facts/Chicxulub_crater/qVqCqm81">Chicxulub crater</a>. Similarly, an iridium anomaly in core samples from the Pacific Ocean suggested the <a href="/facts/Eltanin_impact/psLQ8RV7">Eltanin impact</a> of about 2.5 million years ago.

Iridium open-in-new

Iridium