Iridium

Iridium is a hard, silvery metal from the platinum family and the most corrosion-resistant metal known. Smithson Tennant discovered it in 1803, alongside osmium, and named it after Iris, the Greek goddess of the rainbow, because its salts come in many colors. It is very rare and is a by-product of platinum and nickel mining.

Iridium tips last for years in spark plugs, and iridium crucibles hold molten materials while special crystals are grown for lasers and electronics. In 1980, Luis and Walter Alvarez reported a thin layer of iridium-rich clay laid down worldwide about 66 million years ago. Iridium is rare in Earth's crust but common in asteroids, pointing to the impact that wiped out the dinosaurs.