Iridium
Element 77 · Transition Metal
Iridium is a hard, silvery-white metal that resists corrosion better than any other — even aqua regia barely touches it. It is dense, brittle, melts high, and commonly takes +3 and +4 states.
That toughness puts iridium in spark plugs, crucibles, and pen nibs that must survive extreme conditions. Geologically it is a detective's clue: a worldwide iridium-rich clay layer, 66 million years old, records the asteroid impact that wiped out the dinosaurs, since iridium is rare in Earth's crust but common in meteorites.
Key facts
| Atomic number | 77 |
|---|---|
| Atomic weight | 192.22 |
| Category | Transition Metal |
| Group / Period | 9 / 6 |
| Block | d |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d7 |
| Common oxidation states | +4, +3 |
| State at STP | Solid |
| Electronegativity | 2.20 |
| Density | 22.56 g/cm³ |
| Melting point | 2446 °C |
| Boiling point | 4428 °C |
Occurrence
Iridium occurs in platinum ores and nickel deposits, and arrives from space in meteorites. South Africa is the leading producer.
Applications
Long-life spark plugs
Crucibles for crystal growth
Fountain pen nibs
Electrical contacts
Common compounds
- iridium dioxide
- iridium trichloride
A worldwide layer of iridium-rich clay marks the impact 66 million years ago that wiped out the dinosaurs — iridium is rare on Earth but common in asteroids.
Data source: IUPAC standard atomic weights 2021