|Atomic mass||192.22 amu|
Iridium, discovered in 1804, was named after the Latin word iris, meaning "rainbow". It was so named because of its colourful salts.
Iridium is the most corrosion-resistant of all known metals. It can even withstand attack with hot aqua regia and can be used routinely at temperatures up to 2000°C. Because it is extremely hard, it is very difficult to machine into useful shapes. Where other metals become less brittle after annealing (a process of heating and slowly cooling), iridium becomes brittle and completely unworkable.
Iridium is known as a "platinum metal" because it is found in natural deposits of platinum and along with osmium, its twin element. So, the three elements, osmium, iridium, and platinum are found together, both in nature and on the periodic table of the elements.
Iridium's most common application is as an alloying agent for hardening platinum. Its alloys make bars used as standard weights and measures. The international "standard meter" is platinum-iridium.