Isomer Isomers Isomorphous Isotope Isotopes Isotopic Tracer Iridium , symbol Ir, white, brittle, extremely hard, metallic element.
Iridium is extremely inert chemically, resisting even the action of aqua regia .
In its chemical compound s it forms tetravalent and trivalent salts. It is an extremely rare metal, ranking 77th in order of abundance of the elements in the crust of the earth. The atomic weight of iridium is 192.22. Iridium and osmium are considered the most dense elements. Iridium is found in alluvial deposits alloy ed with platinum as platiniridium and with osmium as osmiridium.