Iridium

Iridium
Properties
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.