Iridium

Smithson Tennant, an English chemist, discovered iridium in 1803 in the residue of crude platinum, after dissolving it in aqua regia, a mixture of nitric and hydrochloric acids. Because of the bright colors of iridium’s salts, Tennant named the element after the Greek goddess Iris—who was known for leaving behind a rainbow.

Much like its supernatural namesake, iridium does not appear naturally on the Earth’s surface. Iridium has extraterrestrial origins and only a very thin layer of iridium exists in the Earth's crust. The iridium on earth was likely caused by a large meteor or asteroid hitting the Earth, because meteors and asteroids contain such high levels of iridium.

Iridium is white and looks like platinum but has a slight yellow tinge. Because of its brittleness, hardness, and high melting point, solid iridium is difficult to shape and mold, so it's often used in its powder form instead.

If elements had personalities, iridium would be the queen of chill. Iridium is unbothered by acids (including aqua regia), unchanged by air, and unconcerned with water (it's the most corrosion-resistant metal!).

But when there’s oxygen around and at high temperatures, iridium does react with cyanide salts, halogens, and oxygen itself. Iridium also reacts directly with sulfur (at atmospheric pressure) and creates iridium disulfide.

Iridium is used for coating optical lenses to reduce glare and improve clarity in certain lighting conditions. It also helps reduce the amount of scratching that might appear on camera and telescope lenses. But don’t get this element in your eyes: it can cause irritation!

Important compounds of iridium are chlorides and iodides that are used as industrial catalysts. Catalysts help speed up chemical reactions, but unlike other chemicals in the reaction, a catalyst is not used up.

Iridium is mostly used in alloys. Osmium-iridium alloys are used for fountain pen nibs and for compass bearings. Iridium appears in solid form, also, but it is very brittle and difficult to work with.

Iridium is mostly found in igneous deposits (volcanic) and asteroid impact craters. The largest known iridium reserves are located in South Africa (near the largest known asteroid impact site, the Vredefort impact structure). There are other deposits in large copper–nickel deposits in Russia and an asteroid impact crater in Canada. Smaller reserves are found in the United States.

Iridium is also found in small deposits with platinum in alluvial (running water) deposits.