WHAT is Iridium

Iridium is a chemical element, and one of the transition metals on the periodic table. Iridium appears as symbol Ir on the periodic table and has an atomic weight of 192.217 and a density of 22.56 g/cm³, making it the second densest known element. Because iridium is so expensive, it is typically used only in applications that require a very small amount of the element. 


Iridium is the most corrosion-resistant metal on Earth. It is extremely difficult to melt, and because of its high melting point, it is hard to form, machine or work iridium. It is also one of the rarest elements in Earth's crust. The huge asteroid that many scientists believe wiped out the dinosaurs 65 million years ago is also thought responsible for the thin layer of iridium-rich clay found around Earth. This layer of iridium forms the Cretaceous-Tertiary boundary. It is also known as the K-T Boundary because the Cretaceous is represented by the letter K.

History of Iridium

The English chemist Smithson Tennant discovered iridium. He found the element in the residues from a solution of platinum ores in 1803. He named the metal Iridium after Iris, who was the personification of the rainbow in Greek mythology, because iridium salts are vibrant and multicolored. Because of its extremely high melting point, it wasn’t until 1842 that scientists could isolate it in a high-purity state. Iridium is also one of the rarest elements on earth, with gold being 40 times more common in the earth’s crust than iridium.

German chemist Rudolf Ludwig Mössbauer won the Nobel Prize in physics in 1961 for for his research, using iridium, concerning the resonance absorption of gamma radiation, a phenomenon now called the Mössbauer effect.

Applications of Iridium

Iridium’s very high melting point makes it useful in many industrial applications, like the construction of high-grade spark plugs used in general aviation aircraft. Manufacturers also use it in the construction of crucibles, or containers for melting and manipulating other industrial metals. Iridium crucibles have most recently helped manufacture sapphire crystals, which require temperatures above 2,000 degrees celsius. Given that iridium’s melting point is 2,446 degrees celsius, pure iridium performs well at the temperatures required. Manufacturers also combine iridium with osmium to make fountain pen nibs, and to construct pivot bearings and other scientific and specialized equipment.