Iridium
| Iridium | |
|---|---|
| Properties | |
| Atomic symbol | Ir |
| Atomic number | 77 |
| Classification | Transition Metals |
| Atomic mass | 192.22 amu |
| Number of Stable Isotopes | 2 |
| Density (grams per cc) | 22.560 g/cm^3 |
| Other Information | |
| Date of discovery | 1803 |
| Name of discoverer | Smithson Tennant |
| Name origin | From the Latin iridis, meaning rainbow. |
| Uses | Used in conjunction with osmium to tip gold pen points, to make crucibles and other high-temperature containers. Also used to make alloys for standard weights and measures, as well as heat-resistant alloys. In addition, used in cancer irradiation, hypodermic needles, helicopter spark plugs and as hardening agent for platinum. |
| Obtained from | Found in gravel deposits with platinum, iridosmium, and osmiridium ores. |
Iridium is an element in the transition metals class of the periodic table. It is hard and lustrous, and is perhaps the most corrosion-resistant metal known. It has the second-highest density of all elements, after osmium.
An alloy of platinum and iridium was used in the international standard meter bar, before the standard was changed in 1960. A similar alloy is still used in the international standard kilogram.
Iridium has provided evidence for a leading theory explaining the extinction of the dinosaurs. There is a worldwide geologic layer, enriched in iridium, apparently deposited about 65 million years ago. This was the time of the cretaceous/tertiary boundary, when many species, most famously the dinosaurs, became extinct. Asteroids have a higher iridium content than the Earth's crust, suggesting that the layer was caused by widespread dispersal of matter from a comet or asteroid strike. Many scientists believe that such a strike, or several strikes, caused the cretaceous/tertiary boundary event, and that the (now buried) Chicxulub crater in what is now the Yucatan peninsula of Mexico was the impact site. The debris from the impact may have blocked sunlight, damaging the food chain.
The Chicxulub impact is not the only theory behind the extinction. Another theory is that it was caused by particularly noxious volcanos in what is now India.
In any case, the iridium did not kill the dinosaurs; the worldwide darkening of the skies did.
