Where Iridium Is Found

Iridium is one of the rarest elements on earth, and accounts for only 1/1000 ppm in the earth's crust. However, as iridium is a very dense metal, second only to osmium in weight, it is thought that most of the available iridium has descended to the earth's core, where it is occasionally spewed out by volcanic eruptions. Not only is iridium very dense and heavy, but it also bonds with any available iron, which also makes up a good part of the core. Platinum is a good source for iridium, as is nickel, osmium, and meteorites.

South America was once the world's major producer of platinum and the Spanish government basically forbid its export. Platinum had been used by the indigenous inhabitants for centuries, but had been taken from alluvial deposits, rather than mined. An English chemist, Smithson Tennant, refined iridium out of smuggled platinum in 1803. Spain's death grip on platinum was broken when the metal was discovered in the Ural Mountains of Russia, which also tried to control the supply, although this ultimately proved to be as effective as the Spanish ban on exporting the metal. Mining operations are still being carried on at the Russian deposit to the present day.

While the role of South America has faded as regards platinum, and so iridium, South Africa is now the largest source for platinum in the world. An enormous reef of platinum bearing ore was discovered in the Transvaal region in the mid-19th century. Most of the platinum group of metals was able to be refined from this reef, including iridium. Today, South Africa still produces the greatest amount of platinum, and hence iridium, in the world.

Besides being found in deposits of noble metals, platinum is also found in nickel and copper deposits, although in a lesser quantity. Sudbury, Canada, produces a relatively small amount of platinum from its nickel deposits, and an even smaller deposit exists in the United States. Extraterrestrial meteorites are often quite rich in iridium, with concentrations above what is generally found in the earth's crust. While stony meteorites will contain some iridium, it is the iron meteorites that will have a greater proportion of iridium, reflecting iridium's ability to bond to iron. In fact, the Willamette Meteorite contains 4.7 ppm of iridium. The meteorite has a rather interesting history beginning with its impact with earth, its transport in glacial flood water to Oregon, and its discovery by a man who stole it to claim it as his own, ultimately spending 3 months to drag the meteorite to his property. The original owners had the meteorite restored to them, but that was not the end of the story. The Willamette Meteorite was shown at the Lewis and Clark Exposition in 1905, then was given to the American Museum of Natural History. The meteorite found its final (we hope) home at the Hayden Planetarium in New York City.