Iridium (Ir, element 77, CAS 7439-88-5) is a hard, brittle, silvery-white transition metal and one of the six platinum group metals, with a density of 22.562 g/cm³ and a melting point of 2,446 °C. It is the most corrosion-resistant metal known, the second-densest element after osmium and one of the scarcest: world primary supply is about 7.1 tonnes (229,000 troy ounces) a year. Its identity data, properties, sources, discovery, uses, compounds, alloys, isotopes, toxicity and rarity follow in that order.
What Is Iridium?#
Iridium is a platinum group metal in period 6, group 9 of the periodic table, with the symbol Ir and atomic number 77. It is a chemical element, a d-block transition metal and a noble metal, sitting between osmium (76) and platinum (78) and directly below rhodium in group 9. Iridium is one of six platinum group metals, a family that shares its ores, its refining route and its resistance to acids.
Iridium Identity: Symbol, Atomic Number and CAS Number#
Iridium's identity numbers are symbol Ir, atomic number 77, CAS 7439-88-5 and standard atomic weight 192.217(2), unchanged since CIAAW's 2017 revision. The identity table below lists the six values that fix iridium in every chemical database.
| Identifier | Value | Source |
|---|---|---|
| Symbol | Ir | IUPAC |
| Atomic number (Z) | 77 | IUPAC |
| CAS Registry Number | 7439-88-5 | CAS, via PubChem element 77 |
| Standard atomic weight | 192.217(2) | CIAAW, revised 2017 |
| Period / group / block | 6 / 9 / d-block | IUPAC periodic table |
| Electron configuration | [Xe] 4f¹⁴ 5d⁷ 6s² | CRC-derived element data |
| Crystal structure | Face-centered cubic, a = 383.92 pm at 20 °C | CRC-derived element data |
Iridium's atomic weight carries an uncertainty of only ±0.002, about 16 times tighter in relative terms than osmium's 190.23(3), because CIAAW flags no natural variation in iridium's isotopic composition.
Iridium Quick Facts#
Iridium's headline facts are its density (22.562 g/cm³, second only to osmium), its brittleness despite a face-centered-cubic structure, and its 1803 discovery alongside osmium. The quick-facts table gathers the values most often searched.
| Property | Value |
|---|---|
| Density, 20 °C | 22.562 g/cm³ (22,562 kg/m³; 0.815 lb/in³) |
| Melting point | 2,446 °C (2,719 K; 4,435 °F) |
| Boiling point | 4,130 °C (4,403 K), CRC lineage; 4,428 °C (4,701 K), PubChem lineage |
| Common oxidation states | +3, +4 (full range −3 to +9) |
| Hardness | Mohs 6.5; Vickers 1,760-2,200 MPa |
| Discovered | 1803, Smithson Tennant |
| Named after | Iris, Greek goddess of the rainbow |
| Largest use | Electrochemical anodes and electrodes (42% of 2025 demand, Johnson Matthey) |
| World primary supply, 2025 | 229 koz (7.1 t), Johnson Matthey |
Iridium Properties#
Iridium is one of the densest and stiffest metals known, at 22.562 g/cm³ and a Young's modulus of 528 GPa. Stiffness and density come with a melting point above 2,400 °C, resistance to every single acid and a brittle, hard-to-work metal body.
Iridium Density: Is It the Densest Element?#
Iridium is the second-densest element at 22.562 g/cm³ (20 °C), narrowly behind osmium at 22.587 g/cm³ (CRC-derived crystallographic values), a 0.11% gap. J. W. Arblaster's recalculations in Platinum Metals Review (2010 for iridium, 2013 for osmium) give 22.562 and 22.589 g/cm³, a 0.027 g/cm³ gap; either pair puts osmium first.
Crystallographic density is calculated, not weighed: four atoms per face-centered-cubic cell, times 192.217 g/mol, divided by Avogadro's constant and a cell edge of 383.92 pm cubed, returns 22.56 g/cm³. Older bulk measurements under-read porous osmium, which is why legacy Johnson Matthey tables list iridium (22.65) above osmium (22.61), and why PubChem still prints 22.42 for iridium. In practical terms, a troy ounce of iridium is a cube about 1.11 cm on a side, and a kilogram is a cube about 3.54 cm on a side.
Temperature does not reverse the ranking. Arblaster's 2014 paper "Is Osmium Always the Densest Metal?" (Johnson Matthey Technology Review) finds osmium densest at ambient pressure at all temperatures; iridium overtakes it only above 2.98 GPa at room temperature, where both reach 22.750 g/cm³. Osmium vs iridium density, hardness and melting data are compared line by line on osmium vs iridium.
| Property | Iridium | Osmium |
|---|---|---|
| Density, 20 °C (g/cm³) | 22.562 | 22.587 |
| Crystal structure | Face-centered cubic | Hexagonal close-packed |
| Melting point | 2,446 °C | 3,033 °C |
| Mohs hardness | 6.5 | 7.0 |
| Vickers hardness (MPa) | 1,760-2,200 | 4,137 |
| Young's modulus (GPa) | 528 | 556 |
| Thermal expansion, 20 °C (10⁻⁶ K⁻¹) | 6.47 | 4.99 |
| Discovered | 1803, Tennant | 1803, Tennant |
Iridium Melting Point, Hardness and Corrosion Resistance#
Iridium melts at 2,446 °C (2,719 K) and is the most corrosion-resistant metal known, resisting aqua regia and every other single acid. The 2,446 °C value is the CRC handbook figure; WebElements gives 2,466 °C. The boiling point is split by about 300 K between source lineages: 4,403 K (CRC) and 4,701 K (PubChem, WebElements), because refractory-metal boiling points are extrapolated from vapor pressure, not measured directly.
Iridium's hardness is Mohs 6.5 and Vickers 1,760-2,200 MPa, and its Young's modulus of 528 GPa is the highest of any face-centered-cubic metal and second among all metals to osmium's 556 GPa. Massive iridium is not attacked by acids; ignited iridium is insoluble in all acids, and chlorine, or hot concentrated hydrochloric acid with sodium perchlorate, is needed to dissolve it. Refiners exploit this: iridium and osmium stay behind as insoluble powder when platinum dissolves in aqua regia. Iridium vs platinum properties are compared on iridium vs platinum.
Iridium Electron Configuration, Oxidation States and Magnetism#
Iridium reaches an oxidation state of +9 in the gas-phase cation [IrO₄]⁺, the highest confirmed for any element, though its common states are +3 and +4; the metal itself is weakly paramagnetic (+25.6 × 10⁻⁶ cm³/mol). Its ground-state configuration, [Xe] 4f¹⁴ 5d⁷ 6s², follows the textbook filling order, which only iridium and osmium do among the six platinum group metals plus gold and silver.
Iridium's magnetic susceptibility of +25.6 × 10⁻⁶ cm³/mol at 298 K is small and positive, the second-weakest response of the six platinum group metals after osmium (+11) and about one-eighth of platinum's (+201.9). No platinum group metal is ferromagnetic in pure form.
Where Iridium Comes From#
Iridium comes from the platinum ores of South Africa's Bushveld Complex, above all its UG2 chromitite layer. South Africa supplies more than 80% of world primary iridium (IPA/SFA, 2026); southern Africa as a whole accounts for up to about 95% (Johnson Matthey, 2022). Iridium is never mined for itself: every gram is a co-product of platinum, palladium or nickel mining, so its output does not respond to its own price.
Iridium Ore and Minerals#
Iridium occurs in native iridium (an Ir-Os-Ru alloy) and in the mineral irarsite, both concentrated in chromite-associated ore alongside osmium and ruthenium. Native iridium, (Ir,Os,Ru), has a hardness of 6-7 and a density of 22.66, among the densest natural substances; irarsite is (Ir,Ru,Rh,Pt)AsS. Iridium also sits in solid solution in pyrrhotite and in laurite-erlichmanite sulfides.
Ore type decides the grade. Implats-derived 6E metal splits put iridium at 2.6-3.7% of UG2 output against 0.8-2.0% in the Merensky Reef; Zimplats and Mimosa report 1.8-2.0% in Zimbabwe's Great Dyke. Ophiolite chromitites are iridium-rich relative to platinum but have never been mined for it.
Iridium Supply and Production#
World primary iridium supply is about 7.1 tonnes a year, against rhodium's 21.8 tonnes, a ratio of roughly 3.1 to 1 (Johnson Matthey, PGM Market Report, May 2026). The table compares 2025 primary supply for four platinum group metals on that single Johnson Matthey basis.
| Metal | 2025 primary supply (koz) | Tonnes | Multiple of iridium |
|---|---|---|---|
| Platinum | 5,557 | 172.8 | 24.3× |
| Ruthenium | 972 | 30.2 | 4.2× |
| Rhodium | 701 | 21.8 | 3.1× |
| Iridium | 229 | 7.1 | 1.0× |
Primary supply only, Johnson Matthey PGM Market Report, May 2026; never combined with secondary supply.
Iridium supply has held between 218 and 237 koz (6.8-7.4 t) every year from 2021 to 2026 (forecast). Johnson Matthey publishes no secondary-supply line for iridium; its demand figures are net of closed-loop recycling. The series is also heavily revised: the May 2026 report cut 2021 supply from 259 to 235 koz, a 9.3% change, so any single-vintage iridium number carries roughly ±10%. The United States imported 1,360 kg in 2024 and an estimated 2,200 kg in 2025 (USGS, Mineral Commodity Summaries 2026). Demand, deficits and electrolyzer growth in the iridium market are covered on the iridium market.
Iridium Discovery and History#
Iridium was discovered in 1803 by Smithson Tennant, who reported it to the Royal Society on 21 June 1804 alongside osmium, from the same insoluble platinum-ore residue. Joseph Louis Proust took the residue for graphite, and in 1803 Collet-Descotils, Fourcroy and Vauquelin named it "ptène" as one new metal. Tennant showed it held two; Collet-Descotils keeps independent partial credit for iridium. Tennant named iridium after Iris, goddess of the rainbow, for the varied colors of its salts, not of the metal, and received the Copley Medal in 1804.
Four milestones, listed below, turned the element into a workable material.
- 1813: John George Children first melted iridium with a powerful galvanic battery.
- 1834: John Isaac Hawkins made the first iridium-pointed gold pen nibs.
- 1860: Deville and Debray achieved significant melting, burning more than 300 liters of oxygen and hydrogen per kilogram.
- 1880: John Holland and William Lofland Dudley patented a phosphorus-addition melting process.
Iridium Uses, Compounds and Alloys#
Iridium's uses, compounds and alloys rest on three properties: corrosion resistance, a 2,446 °C melting point and catalytic activity.
What Is Iridium Used For?#
Iridium is used mainly in oxide-crystal-growth crucibles, spark plug electrodes, PEM electrolyzer anode catalysts and phosphorescent OLED emitters. Johnson Matthey's May 2026 report puts 2025 demand at 236 koz: electrochemical uses 100 koz (42%), other uses 69 koz (29%), chemical 34 koz (14%) and electrical and electronics 33 koz (14%).
| Use | Iridium form | Sector |
|---|---|---|
| Chlor-alkali and electrowinning anodes | IrO₂ coating (dimensionally stable anodes) | Electrochemical |
| PEM electrolyzer anodes | IrO₂ oxygen-evolution catalyst | Hydrogen |
| Czochralski crystal-growth crucibles | Iridium metal | Electronics, lasers |
| Spark plug electrodes | Iridium or platinum-iridium tips | Automotive |
| Green phosphorescent OLED emitter | fac-Ir(ppy)₃ | Displays |
| Cativa acetic acid process | Iridium catalyst, iodide-promoted | Chemical |
| Weld radiography, brachytherapy | Iridium-192 sources | Industrial, medical |
Crucibles work because iridium retains good mechanical properties above 1,600 °C, the heat needed to grow oxide single crystals. Iridium crucibles run under inert or slightly reducing gas, since in hot air the metal is lost as volatile IrO₃. Specifications are on iridium crucibles.
Electrolysis is the growth use. A PEM electrolyzer needs about 400 kg of iridium per gigawatt today (US DOE, 2022), against a 2030 target of 80 kg/GW (WPIC, 2023), so one year of world supply would build roughly 18 GW. Johnson Matthey expects 2026 to bring the first significant PEM demand, from projects in Germany and Portugal. At 400 kg/GW, iridium is not a binding constraint on today's deployment; it becomes one at about 15-25 GW of PEM a year.
Iridium electrodes carry the older electrochemical demand: iridium oxide coatings on dimensionally stable anodes produce chlorine, treat water and make copper foil for lithium batteries and circuit boards. Grades and specifications are covered on iridium electrodes.
Iridium Compounds#
The traded iridium chemical is hexachloroiridic acid hexahydrate, H₂IrCl₆·6H₂O, at roughly 35-40 wt% iridium, the feedstock for electroplating and catalyst anodes. The compound table lists six commercially or scientifically central iridium compounds with their CAS numbers.
| Compound | Formula | CAS | Primary use |
|---|---|---|---|
| Hexachloroiridic acid hexahydrate | H₂IrCl₆·6H₂O | 16941-92-7 | Anode coatings, iridium plating |
| Iridium(III) chloride hydrate | IrCl₃·xH₂O | 14996-61-3 | Precursor for catalysts and OLED emitters |
| Iridium(IV) oxide | IrO₂ | 12030-49-8 | PEM electrolyzer and chlor-alkali anodes |
| Vaska's complex | trans-IrCl(CO)(PPh₃)₂ | 14871-41-1 | Benchmark for oxidative addition |
| Crabtree's catalyst | [Ir(cod)(py)(PCy₃)]PF₆ | 64536-78-3 | Hydrogenation of hindered alkenes |
| fac-Tris(2-phenylpyridine)iridium | fac-Ir(ppy)₃ | 94928-86-6 | Green OLED emitter, photoredox catalyst |
Iridium(iii) chloride comes in two grades: anhydrous IrCl₃ (CAS 10025-83-9) is insoluble, while the water-soluble hydrate is the working precursor sold on a 50-58% iridium assay (Strem, Sigma-Aldrich). Details are on iridium(iii) chloride.
Two complexes made iridium a textbook metal. Vaska's complex, reported by Lauri Vaska and J. W. DiLuzio in 1961, binds oxygen reversibly. Crabtree's catalyst (Crabtree, Felkin and Morris, 1977) hydrogenates tetrasubstituted 2,3-dimethylbut-2-ene at a turnover frequency of 4,000 h⁻¹, a substrate on which Wilkinson's catalyst is essentially inactive (Crabtree, Accounts of Chemical Research, 1979). In OLEDs, iridium's spin-orbit coupling lets fac-Ir(ppy)₃ harvest both singlet and triplet excitons, for internal quantum efficiency approaching 100% against a 25% ceiling for fluorescent emitters.
Iridium(iv) oxide is a blue-black rutile-structure solid (density 11.66 g/cm³) and essentially the only oxide that survives long-term at an acidic, oxidizing PEM anode; ruthenium dioxide is more active but corrodes. Its hazard and grade data are on iridium(iv) oxide.
Iridium Alloys#
The best-known iridium alloy is Pt-10Ir (90% platinum, 10% iridium), used for the International Prototype Kilogram and Meter from 1889 until the kilogram's redefinition on 20 May 2019. Johnson Matthey manufactured the kilogram cylinder, about 39 mm high and wide, in London in 1879, and the 1st CGPM sanctioned it in 1889. Iridium was chosen because it hardens platinum without losing its oxidation resistance: pure platinum measures 56 HV, while Pt-50Ir exceeds 500 HV (Wikipedia's platinum-iridium alloy data).
Pure iridium itself is alloyed for ductility. Additions of 0.2% each of titanium and zirconium reduce its brittleness, and DOP-26 (iridium with 0.3 wt% tungsten and about 60 ppm thorium) clads radioisotope thermoelectric generators. Osmiridium, a natural osmium-iridium alloy, tipped pen nibs and compass pivots through the 19th and 20th centuries.
Iridium Isotopes and Radioactivity#
Iridium has two naturally occurring isotopes, iridium-191 (37.23%) and iridium-193 (62.77%), both observationally stable; no decay has ever been recorded for either (abundances: CIAAW). Natural iridium is therefore not radioactive. Three artificial isotopes matter, listed below.
- Iridium-192: half-life 73.820 days, made by neutron activation of iridium-191, specific activity 341 TBq/g; decays 95.24% to platinum-192. It is the workhorse gamma source for weld radiography and high-dose-rate brachytherapy, and it accounts for most US NRC-tracked incidents of lost or stolen radioactive material.
- Iridium-192m2: half-life 241 years, the longest-lived iridium nuclear isomer.
- Iridium-191m: half-life 4.899 seconds, eluted from an osmium-191 generator for first-pass cardiac imaging.
Iridium-191 also holds a place in physics: Rudolf Mössbauer first demonstrated recoil-free gamma resonance in it in 1957, work recognized with the 1961 Nobel Prize in Physics.
Is Iridium Toxic?#
Iridium has no listed OSHA, NIOSH or ACGIH occupational exposure limit, reflecting the metal's near-total chemical inertness. The table compares iridium and its compounds with its neighbors (OSHA Table Z-1 and NIOSH data retrieved 6 August 2026; GHS data from PubChem's aggregated ECHA notifications).
| Substance | Workplace limit (8-h TWA) | GHS hazard statements |
|---|---|---|
| Iridium metal | None listed | See supplier SDS |
| Iridium(III) chloride, anhydrous | None listed for iridium | H302, H315, H319, H335, H411 |
| Iridium(IV) oxide | None listed for iridium | H272 (oxidizer), H413 |
| Platinum, soluble salts (as Pt) | 0.002 mg/m³ (OSHA, NIOSH, ACGIH) | Compound-specific |
| Rhodium, soluble compounds (as Rh) | 0.001 mg/m³ (NIOSH, ACGIH) | Compound-specific |
Radiological risk comes from sealed iridium-192 sources, not from the metal.
How Rare Is Iridium?#
Iridium is rare because it is strongly siderophile: most of Earth's primordial iridium sank into the core, leaving the crust so iridium-poor that the element anomaly at the 66-million-year-old Cretaceous-Paleogene boundary is cited as evidence of the Chicxulub asteroid impact. Luis Alvarez's team proposed that impact in 1980 from iridium-rich boundary clay.
On supply, the world produces about 229 koz (7.1 t) of primary iridium a year, one ounce for every 24 ounces of platinum on Johnson Matthey's May 2026 figures, and the IPA/SFA 2026 iridium factsheet finds essentially no open-loop recycling. The USGS estimates iridium's 2025 average at US$4,400/oz, down 9%, which it attributes to increased production and waning investor enthusiasm for the hydrogen market (Mineral Commodity Summaries 2026).
Explore Iridium#
Iridium's current price and its attribute pages sit on their own dedicated pages. The sections below link the live quote, 13 in-depth iridium pages and the five sister metals.
Iridium Price Today#
Iridium is priced as a refiner quote, not on an exchange: no futures contract or benchmark auction covers it. Johnson Matthey's base price quotes iridium sponge in US dollars per troy ounce four times each business day, and Umicore publishes a euro quote. The latest value is $8,150.00 per troy ounce ($262.03 per gram, $262,028.58 per kilogram), 197.1% of the gold price, as of 5 Oct 2026, 15:30 UTC.
The iridium price today page carries that quote in every unit: iridium price today.
Historical averages use a different series, USGS annual averages of Engelhard unfabricated prices.
| Year | Average (USD/troy oz) | Source |
|---|---|---|
| 2021 | 5,158.40 | USGS MCS 2026 (Engelhard, S&P Platts) |
| 2022 | 4,581.93 | USGS MCS 2026 (Engelhard, S&P Platts) |
| 2023 | 4,672.78 | USGS MCS 2026 (Engelhard, S&P Platts) |
| 2024 | 4,810.40 | USGS MCS 2026 (Engelhard, S&P Platts) |
| 2025 (estimate) | 4,400 | USGS MCS 2026 |
Daily moves in the iridium price chart follow the Johnson Matthey base price; see iridium price chart.
One troy ounce equals 31.1034768 g; any troy ounce converter turns a quote into grams or kilograms, as our troy ounce converter does.
Iridium Attribute Pages#
Iridium's 13 attribute pages each take one property from this hub to full depth.
| Attribute | Page | Covers |
|---|---|---|
| Properties | Iridium properties | Physical and chemical data |
| Density | Iridium density | 22.562 g/cm³ and the osmium question |
| Melting point | Iridium melting point | 2,446 °C and the boiling-point split |
| Electron configuration | Iridium electron configuration | [Xe] 4f¹⁴ 5d⁷ 6s², states −3 to +9 |
| Uses | Iridium uses | Demand by application |
| Occurrence | Iridium occurrence | Ores, minerals, UG2 |
| Discovery | Iridium discovery | Tennant, 1803 |
| Isotopes | Iridium isotopes | Iridium-191, -193 and -192 |
| Compounds | Iridium compounds | Chlorides, oxide, complexes |
| Alloys | Iridium alloys | Pt-10Ir, DOP-26 |
| Toxicity | Iridium toxicity | Exposure limits, GHS data |
| Magnetism | Is iridium magnetic | Paramagnetism |
| Rarity | How rare iridium is | Supply, siderophile behavior |
Other Platinum Group Metals#
Iridium's five sister metals share its ores and refining route.
| Metal | Density, 20 °C (g/cm³) | Melting point (°C) |
|---|---|---|
| Platinum (Pt), element 78 | 21.452 | 1,768.3 |
| Palladium (Pd), element 46 | 12.007 | 1,554.9 |
| Rhodium (Rh), element 45 | 12.423 | 1,964 |
| Ruthenium (Ru), element 44 | 12.364 | 2,334 |
| Osmium (Os), element 76 | 22.587 | 3,033 |
Iridium has no exchange contract and no LPPM Good Delivery list, which limits investing in iridium: see investing in iridium.
Iridium-bearing scrap uses the same quote form as scrap platinum, palladium and rhodium: scrap platinum, palladium and rhodium.
Balances for all six metals are on the platinum group metals market page: platinum group metals market.
Iridium FAQ#
What is iridium used for?#
Iridium is used in crucibles for growing oxide crystals, spark plugs, PEM electrolyzer anodes and OLED display emitters. Electrochemical uses, chiefly iridium oxide anodes for chlorine and hydrogen production, took 100 of 236 koz (42%) of 2025 demand, according to Johnson Matthey's May 2026 report.
Is iridium radioactive?#
Iridium's two natural isotopes, iridium-191 and iridium-193, are both stable; the artificial isotope iridium-192 is radioactive and used in industrial radiography and cancer brachytherapy. Iridium-192 has a half-life of 73.820 days and is made by irradiating ordinary iridium with neutrons.
Is iridium magnetic?#
Iridium is paramagnetic, not ferromagnetic: its magnetic response (+25.6 × 10⁻⁶ cm³/mol) is one of the weakest of the six platinum group metals. Only osmium, at +11 × 10⁻⁶ cm³/mol, responds more weakly.
Why is iridium so hard to melt and shape?#
Iridium is hard to melt and shape because it is extremely brittle despite its face-centered-cubic structure and has one of the highest melting points of any metal; John George Children first melted it in 1813 using a powerful galvanic battery. Its welds crack, so solid parts are usually made by powder metallurgy.
Is iridium rarer than gold?#
Iridium is far rarer than gold in annual supply: world primary iridium output is about 7.1 tonnes (229 koz) a year (Johnson Matthey, May 2026), and every gram is a by-product of platinum, palladium or nickel mining. Primary platinum supply alone is 24 times larger.
Is iridium the densest element?#
No: osmium is the densest element at 22.587 g/cm³, narrowly ahead of iridium at 22.562 g/cm³, both at 20 °C. Iridium becomes denser than osmium only under pressure above 2.98 GPa (Arblaster, 2014).