66 million years ago, something wiped out the dinosaurs. The key evidence? A thin layer of clay spanning the entire planet with an abnormally high concentration of iridium. This metal barely exists on Earth, but asteroids are loaded with it. That's how iridium helped solve one of the greatest mysteries in the history of life.
Iridium is the second densest element in the universe: 22.56 g/cm³. A dice-sized cube would weigh over 150 grams. This metal won't dissolve in any acid at room temperature, survives 2,446 °C, and barely wears down. That's why it ends up where permanence matters: spark plugs, spacecraft, and the international mass standard.
Iridium was discovered by English chemist Smithson Tennant in 1803, while analyzing residues left after dissolving platinum ore. He noticed that compounds of the new metal shimmered in many colors — so he named it after Iris, the Greek goddess of the rainbow.
Iridium belongs to the platinum group metals and is one of the rarest elements on Earth. Annual production is just 7–8 tons worldwide. Major sources are South Africa, Russia, and Zimbabwe. Due to its scarcity and unique properties, iridium costs roughly as much as gold.
Metallic iridium is completely inert and non-toxic. You can hold it in your bare hands without any risk. However, finely dispersed iridium powder can irritate eyes and lungs — wear a mask when handling it. The radioactive isotope ¹⁹²Ir, used in medicine and industry, requires strict control: it emits dangerous gamma radiation. All operations with ¹⁹²Ir are performed behind lead shielding.
Iridium is the second densest element: 22.56 g/cm³. A one-liter bottle filled with iridium would weigh 22.5 kg — like a suitcase packed for vacation.
A thin layer of iridium found worldwide in 66-million-year-old rock is the key evidence that an asteroid killed the dinosaurs. Earth has almost no iridium, but meteorites are full of it.
Until 2019, the international kilogram standard was a cylinder made of 90% platinum and 10% iridium. That small object defined what a kilogram meant for the entire world.
The name 'iridium' comes from Iris — the Greek goddess of the rainbow. Iridium compounds truly display vivid red, yellow, green, and blue colors.
Iridium won't dissolve in any acid at room temperature — not even aqua regia, which dissolves gold. It is the most corrosion-resistant metal on the planet.
The Cassini spacecraft, which explored Saturn for 13 years, used iridium shells to protect the plutonium in its radioisotope generators from damage.
| Isotope | Mass (u) | Abundance | Half-life | Decay |
|---|---|---|---|---|
191Ir | 190.960594 | 37.30% | stable | — |
193Ir | 192.962926 | 62.70% | stable | — |
Analysis of platinum ore residue