From the Latin word for rainbow, iris . Iridium and osmium were discovered at the same time by the English chemist Smithson Tennant in 1803. Today, iridium is still obtained from platinum ores and as a by-product of mining nickel .
Pure iridium is very brittle and is nearly impossible to machine.
It is primarily used as a hardening agent for platinum. Platinum-iridium alloys are used to make crucibles and other high temperature equipment. Iridium is also alloyed with osmium to make the tips of fountain pens and compass bearings. Iridium is the most corrosive resistant metal known. A thin, worldwide layer of iridium exists in a layer of sediment that was put down at the end of the Cretaceous period.