Iridium -Ir: (Latin - Iris "rainbow") Atomic number 77
Discovered in 1803 by Smithson Tennant in London U.K., Iridium is a very hard, silvery white
metal. It is one of the rarest metals on Earth, and is classified as part of the platinum
metal family. It is derived as a by-product of Nickel refining. It has a highest resistance
to corrosion and attack from chemicals such as acid, and has extremely high melting point of
4429 degrees. It's second only to Osmium as the hardest element in the world, which gives it
the property of super strength. It is typically used as hardening agent for platinum, and
can be mixed with other elements to make super alloys. Iridium also has a lower electrical
resistance than platinum which makes it an even better material to use for electrical
contacts such as in spark plugs.
A thin, worldwide layer of iridium exists in a layer of sediment that was put down at the
end of the Cretaceous period. Since meteors and asteroids contain a higher percentage of
iridium than the earth's crust, this iridium enriched layer is seen as evidence that the
earth was struck by a large meteor or asteroid at that time. Dust from the impact would
have spread around the globe, depositing the iridium. The dust also would have blocked
the sun for a time, resulting in the extinction of many plant and animal species, including
the dinosaurs.
