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Atomic symbol Ir
Atomic number 77
Classification Transition Metals
Atomic mass 192.22 amu
Number of Stable Isotopes 2
Density (grams per cc) 22.560 g/cm^3
Other Information
Date of discovery 1803
Name of discoverer Smithson Tennant
Name origin From the Latin iridis, meaning rainbow.
Uses Used in conjunction with osmium to tip gold pen points, to make crucibles and other high-temperature containers. Also used to make alloys for standard weights and measures, as well as heat-resistant alloys. In addition, used in cancer irradiation, hypodermic needles, helicopter spark plugs and as hardening agent for platinum.
Obtained from Found in gravel deposits with platinum, iridosmium, and osmiridium ores.

Iridium is an element in the transition metals class of the periodic table. It is hard and lustrous, and is perhaps the most corrosion-resistant metal known. It has the second-highest density of all elements, after osmium.

An alloy of platinum and iridium was used in the international standard meter bar, before the standard was changed in 1960. A similar alloy is still used in the international standard kilogram. An alloy of 90% platinum and 10% iridium is widely used in both the jewelry and chemical industries, because it is strong, hard, beautiful, and impervious to almost all chemicals even at very high temperatures.

A layer of iridium in certain rocks, found all over the world, is part of the evidence implying that an asteroid strike caused the Cretaceous-Tertiary Mass Extinction.


Iridium does not have many "everyday" uses, but a few common ones are:

- Spark plugs.

- Phonograph needles.

- It forms an alloy with osmium used for tipping pens and compass bearings.

- Electrical contacts.

See also