Iridium is found in nature as an uncombined element or in natural alloys; especially the iridiumosmium alloys, osmiridium (osmium-rich), and iridosmium (iridium-rich).
A more convenient approach was used for the international prototype metre of 1870, a bar of platinum-iridium alloy which served as the definition of the meter from 1889 to 1960.
