Iridium (Ir) is a chemical element and one of the platinum metals in Groups 8–10 (VIIIb), Periods 5 and 6, of the periodic table. Iridium is a rare, very dense, silver-white metal used in platinum alloys. While hard and brittle, it becomes ductile at very high temperatures, from 1,200° to 1,500° C (2,200° to 2,700° F). It is one of the densest substances on Earth. Iridium was discovered in 1803 in the acid-insoluble residues of platinum ores. The name iridium comes from the Greek word iris (“rainbow”), referring to the various colors of its compounds. Key properties of iridium:

Where is iridium found in nature?

Iridium, a silver-white metal, is very dense and rare in nature. Pure iridium probably doesn't exist naturally; its abundance in the Earth’s crust is about 0.001 parts per million. Iridium is found in natural alloys with other noble metals such as iridosmine (up to 77% iridium), platiniridium (up to 77%), aurosmiridium (52%), and native platinum (up to 7.5%). Iridium-containing ores have been located in South Africa, Alaska, Myanmar (Burma), Brazil, Russia, and Australia. Iridium is also present in gold-bearing conglomerates, such as those in Witwatersrand, South Africa, and in gold sands, like those of California and Oregon. Iridium is generally produced commercially with other platinum metals as a by-product of nickel or copper production.

What are some properties of iridium?

Iridium (Ir) is a rare, silver-white metal of the platinum group, known for its high density and resistance to corrosion. It is hard and brittle but can be made ductile when white-hot (1,200° to 1,500° C). Iridium stands out as one of the densest substances on Earth and is insoluble in acids, even aqua regia, though it will dissolve in concentrated hydrochloric acid in the presence of sodium perchlorate at high temperatures. Iridium's name comes from the Greek word for rainbow, iris , because many of its compounds are brightly colored. The element, which has an atomic number of 77 and an atomic weight of 192.2, was discovered in 1803.

Why is iridium considered a rare element?

Iridium is considered a rare element because its abundance in the Earth’s crust is very low, approximately 0.001 parts per million. Pure iridium probably does not occur in nature. Iridium is also difficult to prepare and fabricate. Iridium-containing ores can be found in South Africa and Alaska, U.S., as well as in Myanmar (Burma), Brazil, Russia, and Australia. Because of its rarity, iridium is chiefly used in the form of platinum alloys. Platinum-iridium alloys are harder, stiffer, and more resistant to chemical attack than pure platinum.

What are common uses of iridium?

Iridium (Ir) is a rare, very dense, silver-white metal with a variety of uses, often in the form of platinum alloys . These alloys, typically containing 5 to 10 percent iridium, are harder, stiffer, and more resistant to chemical attack than pure platinum. They are used in jewelry , pen points , surgical pins and pivots , and electrical contacts . An alloy of 90 percent platinum and 10 percent iridium is used for the international prototype standard kilogram of mass.

How does iridium's resistance to corrosion make it valuable in industry?

Iridium's high resistance to corrosion, even against strong acids like aqua regia, makes it valuable in several industrial applications. Predominantly, iridium is utilized in the form of platinum alloys . These alloys, containing between 5 to 10 percent iridium, are more workable, harder, stiffer, and more resistant to chemical attack than pure platinum. Platinum-iridium alloys are suited for electrical contacts, sparking points, surgical pins, pivots, and jewelry. Notably, an alloy of 90 percent platinum and 10 percent iridium was used for the international prototype standard kilogram.

iridium

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A periodic table element card for iridium shows its atomic number 77, symbol Ir, atomic weight 192.217, electron configuration, and name. The card indicates iridium is a solid, weakly basic transition metal with a face-centered cubic crystal structure. A color key and icon legend appear below.

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iridium

chemical element

Also known as: Ir

Written and fact-checked by

Britannica Editors

Last updated

Oct. 2, 2026 •History

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What is iridium?
Iridium (Ir) is a chemical element and one of the platinum metals in Groups 8–10 (VIIIb), Periods 5 and 6, of the periodic table. Iridium is a rare, very dense, silver-white metal used in platinum alloys. While hard and brittle, it becomes ductile at very high temperatures, from 1,200° to 1,500° C (2,200° to 2,700° F). It is one of the densest substances on Earth.

Iridium was discovered in 1803 in the acid-insoluble residues of platinum ores. The name iridium comes from the Greek word iris (“rainbow”), referring to the various colors of its compounds.

Key properties of iridium:
- Atomic number: 77
- Atomic weight: 192.2
- Melting point: 2,410° C (4,370° F)
- Boiling point: 4,527° C (8,181° F)
- Specific gravity: 22.4 (20° C)
- Oxidation states: +1, +3, +4
- Electron configuration: [Xe]4f¹⁴5d⁹
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Where is iridium found in nature?
Iridium, a silver-white metal, is very dense and rare in nature. Pure iridium probably doesn't exist naturally; its abundance in the Earth’s crust is about 0.001 parts per million.

Iridium is found in natural alloys with other noble metals such as iridosmine (up to 77% iridium), platiniridium (up to 77%), aurosmiridium (52%), and native platinum (up to 7.5%). Iridium-containing ores have been located in South Africa, Alaska, Myanmar (Burma), Brazil, Russia, and Australia. Iridium is also present in gold-bearing conglomerates, such as those in Witwatersrand, South Africa, and in gold sands, like those of California and Oregon. Iridium is generally produced commercially with other platinum metals as a by-product of nickel or copper production.
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What are some properties of iridium?
Iridium (Ir) is a rare, silver-white metal of the platinum group, known for its high density and resistance to corrosion. It is hard and brittle but can be made ductile when white-hot (1,200° to 1,500° C). Iridium stands out as one of the densest substances on Earth and is insoluble in acids, even aqua regia, though it will dissolve in concentrated hydrochloric acid in the presence of sodium perchlorate at high temperatures.

Iridium's name comes from the Greek word for rainbow, iris, because many of its compounds are brightly colored. The element, which has an atomic number of 77 and an atomic weight of 192.2, was discovered in 1803.
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Why is iridium considered a rare element?
Iridium is considered a rare element because its abundance in the Earth’s crust is very low, approximately 0.001 parts per million. Pure iridium probably does not occur in nature. Iridium is also difficult to prepare and fabricate. Iridium-containing ores can be found in South Africa and Alaska, U.S., as well as in Myanmar (Burma), Brazil, Russia, and Australia. Because of its rarity, iridium is chiefly used in the form of platinum alloys. Platinum-iridium alloys are harder, stiffer, and more resistant to chemical attack than pure platinum.
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What are common uses of iridium?
Iridium (Ir) is a rare, very dense, silver-white metal with a variety of uses, often in the form of platinum alloys. These alloys, typically containing 5 to 10 percent iridium, are harder, stiffer, and more resistant to chemical attack than pure platinum. They are used in jewelry, pen points, surgical pins and pivots, and electrical contacts. An alloy of 90 percent platinum and 10 percent iridium is used for the international prototype standard kilogram of mass.
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How does iridium's resistance to corrosion make it valuable in industry?
Iridium's high resistance to corrosion, even against strong acids like aqua regia, makes it valuable in several industrial applications. Predominantly, iridium is utilized in the form of platinum alloys. These alloys, containing between 5 to 10 percent iridium, are more workable, harder, stiffer, and more resistant to chemical attack than pure platinum. Platinum-iridium alloys are suited for electrical contacts, sparking points, surgical pins, pivots, and jewelry. Notably, an alloy of 90 percent platinum and 10 percent iridium was used for the international prototype standard kilogram.
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iridium (Ir), chemical element, one of the platinum metals of Groups 8–10 (VIIIb), Periods 5 and 6, of the periodic table. It is very dense and rare and is used in platinum alloys. A precious, silver-white metal, iridium is hard and brittle, but it becomes ductile and can be worked at a white heat, from 1,200° to 1,500° C (2,200° to 2,700° F). It is one of the densest terrestrial substances. In the massive state the metal is practically insoluble in acids and is not attacked even by aqua regia. It can be dissolved in concentrated hydrochloric acid in the presence of sodium perchlorate at 125° to 150° C (257° to 302° F).

Because of difficulties in preparation and fabrication, the pure metal has few applications. Iridium is chiefly used in the form of platinum alloys. Platinum-iridium alloys (5 to 10 percent iridium) are readily workable metals that are much harder and stiffer and more resistant to chemical attack than the soft pure platinum. Such alloys are used for jewelry, pen points, surgical pins and pivots, and electrical contacts and sparking points. The international prototype standard kilogram of mass is made from an alloy containing 90 percent platinum and 10 percent iridium.

Pure iridium probably does not occur in nature; its abundance in the Earth’s crust is very low, about 0.001 parts per million. Though rare, iridium does occur in natural alloys with other noble metals: in iridosmine up to 77 percent iridium, in platiniridium up to 77 percent, in aurosmiridium 52 percent, and in native platinum up to 7.5 percent. Iridium generally is produced commercially along with the other platinum metals as a by-product of nickel or copper production.

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Iridium-containing ores are found in South Africa and Alaska, U.S., as well as in Myanmar (Burma), Brazil, Russia, and Australia. In the late 20th century South Africa was the world’s major producer of iridium.

The element was discovered in 1803 in the acid-insoluble residues of platinum ores by the English chemist Smithson Tennant; the French chemists H.-V. Collet-Descotils, A.-F. Fourcroy, and N.-L. Vauquelin identified it at about the same time. The name iridium, derived from the Greek word iris (“rainbow”), refers to the various colours of its compounds. Natural iridium consists of a mixture of two stable isotopes, iridium-191 (37.3 percent) and iridium-193 (62.7 percent). The chemistry of iridium centres on oxidation states of +1, +3, and +4, though compounds of all states from 0 to +6 are known with perhaps the exception of +2. Complexes in oxidation state +1 chiefly contain carbon monoxide, olefins, and phosphines as ligands. The anions hexachloroiridate, [IrCl₆]²⁻, and hexabromoiridate, [IrBr₆]²⁻, are the only notable chemical species containing iridium in the +4 oxidation state. Iridium is somewhat more reactive than ruthenium and osmium.

Element Properties
atomic number	77
atomic weight	192.2
melting point	2,410° C (4,370° F)
boiling point	4,527° C (8,181° F)
specific gravity	22.4 (20° C)
oxidation states	+1, +3, +4
electron config.	[Xe]4f¹⁴5d⁹

The Editors of Encyclopaedia Britannica This article was most recently revised and updated by Rick Livingston.

iridium

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