Iridium is an exceptionally rare, dense, and corrosion-resistant metal. As a member of the platinum group metals, it is the second-densest naturally occurring element. Its resistance to corrosion, even at high temperatures, makes it highly sought after. Its scarcity drives interest in its origins and acquisition.
Iridium’s Presence on Earth
Iridium exists in very low concentrations within Earth’s crust. This scarcity at the surface is largely due to its “siderophilic” or iron-loving nature. During Earth’s early, molten stages, most of the planet’s iridium, being dense and prone to bonding with iron, sank to the core, rendering it largely inaccessible.
Despite its rarity, iridium is found in extractable quantities within specific geological formations, primarily in ultramafic and igneous rocks. These deposits often contain iridium alloyed with other platinum group metals, and sometimes with nickel or copper. Significant terrestrial reserves are located in the Bushveld Igneous Complex in South Africa, a major PGM source. Other notable sources include the Norilsk-Talnakh deposits in Russia and the Sudbury Basin in Canada, where iridium is recovered alongside nickel and copper. Some iridium is also found in alluvial deposits, concentrated by natural erosion.
Iridium from Space
Iridium is more abundant in meteorites and asteroids compared to Earth’s crust. This difference indicates extraterrestrial events. The “iridium anomaly” is a notable example, referring to an unusually high concentration of iridium in a thin, global rock layer.
This iridium-rich layer marks the Cretaceous–Paleogene (K-Pg) boundary. This anomaly provides strong evidence of a massive asteroid impact that caused a major extinction event, including dinosaurs. The Chicxulub crater has been identified as the impact site. The iridium in the boundary layer originated from vaporized asteroid material distributed globally after the collision.
How Iridium is Obtained
Given its rarity, iridium is rarely mined as a primary metal, but primarily acquired as a byproduct during the mining and refining of other metals. These include nickel, copper, and other platinum group metals.
Separating iridium from these metals involves complex metallurgical processes, often including dissolving other platinum group metals and gold, followed by purification steps. Recycling also contributes to the supply of iridium, with recovered material coming from sources like industrial catalysts, electronic components, and high-performance spark plugs.