The element with atomic number 77 that gets its name from the Latin for “rainbow” is iridium. Its symbol is Ir, and it is a silvery-white transition metal in the platinum group.
The name comes from Iris, the Greek goddess associated with the rainbow; the Latin word iris also means “rainbow.” Chemist Smithson Tennant chose the name after discovering iridium in 1803 in residues left when platinum ore was dissolved. The name refers to the striking range of colours displayed by some of its compounds, not to the colour of the pure metal itself.
Iridium is exceptionally dense, hard, and resistant to corrosion. It is slightly less dense than osmium, making osmium the usual answer when a quiz asks for the densest naturally occurring element. Iridium is also rare in Earth’s crust but relatively abundant in some meteorites.
That meteorite connection helped support the theory that an asteroid impact caused the extinction of the non-avian dinosaurs about 66 million years ago: unusually high iridium levels appear in the boundary clay linked to the Chicxulub impact.