Iridium is the most corrosion-resistant element on the Periodic Table of Elements. It also has the highest density of all the elements. Because it resists corrosion, it is used to set standards in weights and measures. But because it is so dense and brittle, it is hard to machine, form or work it unless it is heated to extreme temperatures.
Iridium is a member of the platinum family and is white in color with a yellowish hue. It has a density of 22.65 grams per cubic centimeter. By comparison, the density of lead is 11.34 g/cm3 and the density of iron is 7.874 g/cm3.
Iridium is not affected by acids, bases, or most other strong chemicals. That property makes it useful in making objects that are exposed to such materials.
- Atomic weight (average mass of the atom): 192.217
- Melting point: 4,435 F (2,446 C)
- Boiling point: 8,002.4 F (4,428 C)
- Stable isotopes: 2, which are iridium-191 (37.3 percent) and iridium-193 (62.7 percent)
Today, iridium is commercially recovered as a byproduct of copper or nickel mining. Ore containing iridium is found in Brazil, the United States, Myanmar, South Africa, Russia and Australia.
Pure iridium is so rare on the Earth’s crust that there is only about 2 parts per billion located in the crust, according to Chemistry Explained.
“Iridium is one of the densest and rarest of Earth’s natural elements. It is so dense that it mainly exists in the Earth’s core, rather than crust,” said Amanda Simson, an assistant professor of chemical engineering at the University of New Haven.
But some iridium exists in the crust. In 1980 scientist Luis Alvarez and his son Water Alvarez found significant amounts of iridium in a certain part of the Earth’s crust, spread out all over the Earth’s surface.
Though brittle, iridium can be worked if heated to a white heat of 2,200 to 2,700 degrees Fahrenheit (1,200 to 1,500 degrees Celsius), according to Encyclopedia Britannica. Iridium’s principal use is to harden platinum by making a platinum alloy.
It is also used to make devices needed for high temperatures and in electrical contacts. It is also used on some optical lenses to reduce glare. A compound of osmium and iridium, called osmiridium, is used in fountain pen tips and compass bearings. Super-strong jewelry is also made of an iridium and platinum alloy.