Iridium is a chemical element with symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, iridium is generally credited with being the second densest element (after osmium) based on measured density, although calculations involving the space lattices of the elements show that iridium is denser. It is also the most corrosion-resistant metal, even at temperatures as high as 2000 °C. Although only certain molten salts and halogens are corrosive to solid iridium, finely divided iridium dust is much more reactive and can be flammable.
Three reasons Iridium stands out
1
Used in spark plugs which ignites car fuel.
2
A global layer of this metal in ancient rock is key evidence for the asteroid impact that wiped out the dinosaurs 66 million years ago.
3
It is the most corrosion-resistant metal known, virtually unaffected by any acid or base.
A cosmic clue hidden in clay
Iridium barely corrodes and is rare in Earth’s crust because much of it sank into the core. A worldwide iridium-rich layer marks debris from the asteroid impact associated with the end-Cretaceous extinction. The metal also survives severe conditions in spark plugs, crucibles, and spacecraft components.
Recognizing Iridium in Elementle
If Iridium is the mystery element, guesses below atomic number 77 point up and guesses above it point down. Its symbol is Ir: a green letter matches the same position in that symbol, while a yellow letter belongs in another position.
The family clue turns green for transition metal guesses. Compare Osmium (Os), number 76 and Platinum (Pt), number 78: they share the family clue, but their atomic numbers and symbols help you tell them apart.
Values are reference data, not a specification for every temperature, pressure, or allotrope. Unknown properties are left unavailable. Superheavy-element predictions remain uncertain.
The introduction and original editorial story are adapted from Wikipedia contributors via Periodic-Table-JSON. Element descriptions and their adaptations are available under CC BY-SA 3.0. Numerical attributes use the PubChem periodic-table dataset, retrieved September 22, 2026.