Structure
Not a diagram of dots on rings — a Monte-Carlo sample of the actual probability density |ψ|² for each occupied subshell. Drag to rotate. Blue and violet mark opposite signs of the wavefunction, which is what makes bonding possible.
Measured values
Every bar shows where iridium sits among all 118 elements for that property.
Sources: IUPAC 2021 standard atomic weights · CRC Handbook of Chemistry and Physics · NIST. Values marked ~ are predicted rather than measured.
Size, to scale
Radius 136 pm — that is 0.136 nm, so about 3676 million of them side by side would span a millimetre.
Thermal range
Iridium is liquid over a 1982 K window, from 2719 K to 4701 K.
The story
The most corrosion-resistant metal known, and the fingerprint of the asteroid that ended the dinosaurs.
Iridium's discovery reads like a chemistry detective story. In 1803, English chemist Smithson Tennant was investigating the mysterious black residue left after dissolving crude platinum in aqua regia (a mixture of nitric and hydrochloric acids). While other chemists had dismissed this residue as worthless impurity, Tennant's curiosity would lead to one of chemistry's most spectacular discoveries.
Working in his London laboratory, Tennant noticed that this "worthless" residue wouldn't dissolve in any known acid - a property so unusual it demanded investigation. When he finally managed to dissolve it using extreme chemical methods, something extraordinary happened: the resulting solutions displayed a brilliant array of colors unlike anything seen before in chemistry.
The solutions Tennant created shimmered with every color of the rainbow - deep purples, brilliant yellows, vivid greens, and intense reds. Struck by this spectacular display, he named the new element "iridium" after Iris, the Greek goddess of the rainbow who served as messenger between heaven and earth.
This wasn't just poetic license - the name perfectly captured the metal's most striking chemical property. Different iridium compounds produce distinctly colored solutions, from the deep purple of iridium(IV) chloride to the yellow of iridium(VI) compounds. Even today, this colorful chemistry makes iridium compounds valuable in analytical chemistry.
Tennant's investigation of the platinum residue actually yielded two new elements. Along with rainbow-colored iridium, he discovered osmium, named for its harsh odor. This double discovery made 1803 one of the most productive years in the history of element discovery.
The discovery established Tennant as one of the foremost chemists of his era. His systematic approach to investigating "waste" materials became a model for future element discoveries. Many subsequent elements were found hiding in the residues and byproducts of other chemical processes.
Isolating pure iridium proved incredibly challenging. The metal's extraordinary chemical inertness - the very property that makes it valuable today - made it nearly impossible to work with using 19th-century techniques. Early chemists struggled to produce even small quantities of the pure metal.
The breakthrough came with the development of powder metallurgy techniques. By reducing iridium compounds to metal powder and then compacting and sintering at extreme temperatures, chemists finally obtained workable quantities of this remarkable element.
Iridium's unique properties quickly caught the attention of scientists and royalty alike. The metal's incredible durability and resistance to tarnishing made it ideal for scientific instruments that needed to maintain their precision over decades.
By the mid-1800s, iridium alloys were being used for the most prestigious scientific applications, including the international standard meter and weights used by national laboratories. This early recognition of iridium's exceptional properties foreshadowed its modern role in advanced technology.
Tennant's discovery of iridium demonstrated the importance of investigating apparent "waste products" thoroughly. His work inspired generations of chemists to look more carefully at reaction residues, leading to the discovery of numerous other elements.
Today, iridium stands as perhaps the most extreme example of chemical inertness in the periodic table. Tennant could hardly have imagined that his "rainbow metal" would one day be crucial for space exploration, cancer treatment, and the production of clean hydrogen fuel for a sustainable future.
Applications
Iridium's extraordinary melting point of 2,466°C makes it central in the most demanding aerospace applications. It's used in rocket engine nozzles where extreme temperatures would destroy other materials. NASA uses iridium-lined combustion chambers in spacecraft thrusters, and it's essential in reentry vehicle heat shields for space missions.
In jet engines, iridium components withstand the intense heat of combustion chambers. The metal's resistance to thermal shock makes it perfect for turbine blade coatings in military aircraft engines that operate at extreme temperatures.
Iridium catalysts are revolutionizing green chemistry and industrial processes. In water electrolysis for hydrogen production, iridium-based catalysts are the gold standard for the oxygen evolution reaction (OER). These catalysts are crucial for green hydrogen production from renewable energy sources.
The pharmaceutical industry relies on iridium catalysts for complex organic synthesis reactions. Iridium complexes enable asymmetric hydrogenation reactions that create specific molecular chirality - essential for producing effective medications with minimal side effects.
In petrochemical refining, iridium catalysts facilitate reforming reactions that convert straight-chain hydrocarbons into branched molecules, improving gasoline octane ratings and reducing engine knock.
Iridium's exceptional electrical conductivity and corrosion resistance make it valuable in high-end electronics. It's used in electrical contacts for critical applications where failure isn't an option - from aircraft control systems to medical devices.
In precision measurement, iridium alloys are used in standard weights and measures. The International Bureau of Weights and Measures uses a platinum-iridium alloy for the international prototype meter and kilogram standards.
Spark plug electrodes in high-performance engines use iridium for its durability and consistent performance. These plugs last significantly longer than conventional designs and provide superior ignition characteristics.
Iridium-192 isotope is crucial in industrial radiography for non-destructive testing of welds, pipelines, and structural components. Its gamma radiation properties make it ideal for detecting flaws in critical infrastructure.
In nuclear reactors, iridium components resist neutron bombardment and maintain structural integrity under extreme radiation conditions. Research facilities use iridium crucibles for handling radioactive materials safely.
The luxury watch industry values iridium for its scratch resistance and lustrous appearance. High-end fountain pen nibs often feature iridium tips that provide smooth writing and exceptional durability.
Iridium's rarity and unique properties make it a symbol of exclusivity in luxury goods, from jewelry to limited-edition collectibles where its distinctive properties justify premium pricing.
Your car likely contains iridium in its spark plugs. Iridium spark plugs are the premium choice for high-performance vehicles and motorcycles. They last 4-6 times longer than traditional copper plugs and provide more consistent ignition, improving fuel efficiency and reducing emissions.
Luxury and sports car manufacturers specify iridium plugs for their superior performance characteristics. These plugs maintain their electrode shape longer, ensuring optimal engine performance throughout their extended lifespan.
Premium fountain pens feature iridium-tipped nibs that provide the smoothest writing experience possible. Despite being called "iridium tips," modern pen manufacturers often use iridium alloys that combine durability with flexibility.
These nibs resist wear from paper friction and maintain their shape for decades of use. The iridium tip ensures consistent ink flow and prevents the scratching that occurs with steel nibs over time.
High-end Swiss watches incorporate iridium components for their exceptional scratch resistance and lustrous appearance. Watch cases and movements benefit from iridium's ability to maintain their finish even with daily wear.
Some exclusive timepieces feature pure iridium cases, making them among the most durable and distinctive watches available. The metal's rarity adds to the exclusivity and value of these luxury pieces.
Cancer treatment benefits from iridium-192 sources used in brachytherapy. These radioactive seeds are implanted directly into tumors, delivering targeted radiation while minimizing damage to healthy tissue.
Surgical instruments and medical implants sometimes incorporate iridium alloys for their biocompatibility and resistance to bodily fluids. The metal's inertness makes it safe for long-term contact with human tissue.
Industrial facilities use iridium-192 sources for radiographic testing of pipelines, pressure vessels, and structural welds. This non-destructive testing ensures the safety and integrity of critical infrastructure.
The aviation industry relies on iridium radiography to inspect aircraft components, detecting microscopic flaws that could lead to catastrophic failures. This testing is mandatory for many safety-critical aerospace parts.
Where it comes from
0.001 mg/kg of Earth's crust · more abundant than 32% of elements
Iridium's story begins in the hearts of dying stars. This precious metal forms during supernova explosions and neutron star collisions, making it incredibly rare on Earth's surface. The famous iridium anomaly in Earth's geological record marks the asteroid impact that ended the dinosaur era 66 million years ago.
This thin iridium-rich layer found worldwide provides compelling evidence for the asteroid impact theory of mass extinction. The iridium concentration is hundreds of times higher than normal Earth rocks, matching the composition of asteroids and comets.
Earth's iridium is extraordinarily scarce, with an average crustal abundance of only 0.001 parts per million - making it rarer than gold or platinum. Most accessible iridium sank to Earth's core during planetary formation, leaving only trace amounts in the crust.
The metal is typically found in platinum group metal (PGM) deposits in South Africa's Bushveld Complex, Russia's Norilsk region, and Canada's Sudbury Basin. These deposits formed from ancient magmatic processes that concentrated the platinum group metals.
South Africa produces about 80% of the world's iridium, primarily as a byproduct of platinum and nickel mining. The Bushveld Igneous Complex contains the world's largest known iridium reserves, formed over 2 billion years ago.
Russia is the second-largest producer, with significant deposits in the Ural Mountains and Siberian regions. The Norilsk-Talnakh deposits are particularly rich in platinum group metals, including iridium.
Annual global production is only 3-4 tonnes, making iridium one of the rarest metals actively mined. This scarcity drives its high value and limits its widespread application despite superior properties.
Due to its extreme rarity and high value, iridium recycling is economically crucial. Spent catalysts, old spark plugs, and electronic components undergo sophisticated recovery processes to extract and purify iridium.
A substantial share of supply comes from recycling. Advanced chemical processes can recover iridium from complex alloys and contaminated materials.
Ironically, while rare on Earth's surface, iridium is more abundant in asteroids and meteorites. Some metallic meteorites contain iridium concentrations thousands of times higher than terrestrial rocks.
Future space mining operations may target near-Earth asteroids rich in platinum group metals, potentially making iridium more accessible. A single large asteroid could contain more iridium than all known Earth reserves.
Handling
Metallic iridium is considered one of the safest metals to handle due to its extraordinary chemical inertness. It doesn't react with skin, air, or most chemicals under normal conditions. However, proper precautions should still be observed during handling and processing.
Iridium powder and dust present the primary safety concerns. Fine particles can become airborne and cause respiratory irritation if inhaled. Always use appropriate dust masks (N95 minimum) when working with powdered iridium or during grinding/machining operations.
Skin contact with iridium dust may cause minor irritation in sensitive individuals. Wear nitrile gloves and wash hands thoroughly after handling. Eye protection is essential when working with fine particles.
Iridium-192 is a significant radiation hazard requiring specialized training and equipment. This isotope emits high-energy gamma radiation that can cause severe tissue damage, radiation sickness, and increased cancer risk.
Only licensed radiation safety professionals should handle Ir-192 sources. Storage requires lead-lined containers, and exposure time must be minimized using the ALARA principle (As Low As Reasonably Achievable). Regular radiation monitoring is mandatory.
Emergency protocols must be established for Ir-192 incidents. Exposure can cause acute radiation syndrome within hours. Immediate medical attention and radiation contamination procedures are critical.
High-temperature processing of iridium requires specialized equipment and training. Melting point of 2,466°C means extreme heat hazards and potential for severe burns. Use appropriate heat-resistant PPE and ensure adequate ventilation.
Chemical processing of iridium compounds requires careful handling as some may be more reactive than the pure metal. Follow standard laboratory safety protocols and consult safety data sheets for specific compounds.
Due to iridium's extreme value and rarity, disposal is economically wasteful and environmentally unnecessary. All iridium-containing materials should be recycled through specialized precious metal recovery services.
Iridium poses minimal environmental threat due to its chemical inertness, but proper disposal of radioactive isotopes requires licensed radioactive waste management facilities.
Quick answers
Iridium (symbol Ir) is element 77 on the periodic table, a transition metal in period 6, group 9. The most corrosion-resistant metal known, and the fingerprint of the asteroid that ended the dinosaurs. At room temperature it is a solid.
[Xe] 4f¹⁴ 5d⁷ 6s², giving 6 occupied shells holding 2, 8, 18, 32, 15, 2 electrons respectively.Iridium melts at 2719 K (2445.9 °C) and boils at 4701 K (4427.9 °C). That puts it among the most refractory elements — it stays solid at temperatures that vaporise most metals.
The standard atomic weight of Iridium is 192.217 u. That is a weighted average across its naturally occurring isotopes, which is why it is rarely a whole number.
Iridium has a density of 22.56 g/cm³. Water is 1.0 g/cm³, so a block of iridium is about 22.6× heavier.
Iridium has a Pauling electronegativity of 2.2. The scale runs from 0.70 (francium, the least greedy for electrons) to 3.98 (fluorine, the most). Values in this middle band tend to form covalent rather than strongly ionic bonds.
Iridium was discovered in 1803 by Smithson Tennant. It is named after iris, goddess of the rainbow.
Iridium makes up about 0.001 mg/kg of the Earth's crust — genuinely rare, which is why it is expensive.