Iridium is one of the rarest and most extreme metals on Earth, and its uses reflect that. With a melting point of 2,446°C, a density roughly twice that of lead, and complete resistance to every known acid (including aqua regia, the mixture that dissolves gold), iridium fills roles where no other material can survive. Global production sits at only about 7 tons per year, and the metal costs over $6,500 per ounce, more than six times the price of platinum. That scarcity concentrates its use in high-value applications across energy, medicine, automotive, aerospace, and chemical manufacturing.
Spark Plugs in Cars and Trucks
The most familiar use of iridium for most people is in spark plugs. Iridium’s extremely high melting point allows spark plug tips to withstand the repeated combustion cycles inside an engine without eroding. Manufacturers typically rate iridium spark plugs for 60,000 to 100,000 miles before replacement, a significant jump over platinum plugs, which generally fall short of 25,000 miles. That durability makes iridium plugs especially practical for stop-and-go city driving, highway cruising, and extreme temperature conditions where consistent ignition matters most.
Green Hydrogen Production
Iridium plays a critical role in one of the most promising clean energy technologies: proton exchange membrane water electrolyzers, the machines that split water into hydrogen and oxygen using electricity. Inside these systems, iridium oxide serves as the catalyst that drives the oxygen-producing side of the reaction. No widely available substitute matches its combination of activity and stability in the harsh acidic environment inside the electrolyzer.
The challenge is supply. With only about 7 tons produced globally each year, scaling up hydrogen production demands that engineers use less iridium per device. Recent catalyst designs published in Nature Communications have pushed iridium loading down to 0.28 milligrams per square centimeter while maintaining strong performance and durability over 1,800 hours of operation. That kind of efficiency gain is essential if electrolyzers are going to be manufactured at the scale needed for a hydrogen economy.
Cancer Treatment
A radioactive form of iridium, iridium-192, is used in brachytherapy, a type of radiation treatment where a small radioactive source is placed directly inside or next to a tumor. This approach delivers a concentrated dose of radiation to cancer cells while limiting exposure to surrounding healthy tissue. Iridium-192 brachytherapy has been used for cervical, breast, head and neck, and prostate cancers. In prostate cancer specifically, it serves as an alternative for patients who aren’t candidates for surgery, with clinical follow-up data extending beyond 10 years.
Industrial Chemical Production
Iridium is the key catalyst in the Cativa process, one of the world’s primary methods for manufacturing acetic acid. Acetic acid is a fundamental industrial chemical used to produce everything from vinyl acetate (the basis of paints and adhesives) to food-grade vinegar. The Cativa process, first commercialized in 1995, replaced an older system that relied on rhodium. Iridium proved significantly more stable as a catalyst, allowed the reaction to run with less water, reduced liquid byproducts, and achieved a selectivity above 99% for converting methanol into acetic acid. That efficiency improvement enabled a 20% production increase at the first plant to adopt it.
Rocket Engines and Aerospace
In space, iridium coatings protect rocket combustion chambers and nozzles from temperatures that would destroy most metals. NASA has tested iridium-coated rhenium rocket chambers operating at roughly 2,200°C (4,000°F). At those temperatures, the iridium layer acts as an oxidation barrier, preventing the underlying metal structure from degrading. This design eliminates the need for fuel film cooling, where extra propellant is sprayed along chamber walls purely to keep them from melting. Removing that cooling requirement means more propellant goes toward thrust, improving overall engine performance.
Growing Crystals for Electronics
Sapphire crystals used in electronics, LED substrates, and smartphone camera covers are grown from molten aluminum oxide at temperatures just above 2,050°C. The only practical container for holding this melt is an iridium crucible. Iridium doesn’t react with the molten alumina and maintains its structural integrity at the required temperatures. This crystal-growing technique, called the Czochralski process, has been used since the 1980s to produce sapphire wafers for semiconductor carrier plates, photomasks, and transparent electronic substrates.
Jewelry Alloys
Pure platinum is too soft for everyday jewelry, with a hardness of only about 40 on the Vickers scale. Adding a small percentage of iridium solves this problem. The standard jewelry alloy is 95% platinum and 5% iridium (Pt950/Ir), which provides enough hardness to hold gemstone settings securely while keeping the platinum content high enough to qualify as a premium metal. A slightly lower grade, Pt900/Ir with 10% iridium, offers even greater hardness for pieces that need more structural strength.
Why Iridium Is So Scarce
Iridium’s crustal abundance is just 0.001 parts per million, making it roughly five times rarer than platinum in the Earth’s crust. Nearly all of the world’s supply comes as a byproduct of platinum and nickel mining, primarily in South Africa. That 7-ton annual production figure is tiny compared to platinum’s roughly 200 tons per year. The combination of extreme scarcity, rising demand from the hydrogen energy sector, and irreplaceable performance in high-temperature and catalytic applications keeps iridium among the most expensive metals on the planet.
In its pure metallic form, iridium poses minimal health risk. Safety data sheets list potential skin and eye irritation from fine iridium powder but note no established exposure limits from major regulatory agencies and no classification as a carcinogen. The greater concern around iridium isn’t toxicity but supply: whether the planet produces enough of it to support the clean energy technologies that increasingly depend on it.