iridium
Americannoun
noun
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A rare, whitish-yellow element that is the most corrosion-resistant metal known. It is very dense, hard, and brittle, and is is used to make hard alloys of platinum for jewelry, pen points, and electrical contacts. Atomic number 77; atomic weight 192.2; melting point 2,410°C; boiling point 4,130°C; specific gravity 22.42 (at 17°C); valence 3, 4.
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See Periodic Table
Closer Look
In 1978 geologist Walter Alvarez discovered a high concentration of iridium in a layer of clay that had formed between the Mesozoic and Cenozoic eras, a period about 65 million years ago during which dinosaurs and many other organisms became extinct. This finding was significant as iridium is rare at Earth's surface (an unusually high concentration is called an iridium anomaly). Most surface iridium is thought to come from dust created when meteors disintegrate in the atmosphere or collide with Earth. Alvarez's father, the physicist Luis Alvarez, suggested that the iridium might have come from the impact of a meteor about 10 km (6.2 mi) across. Such an impact would have caused an enormous explosion, sending huge clouds of dust into the atmosphere. The dust, blocking out the Sun and causing extensive acid rain, would have triggered a worldwide ecological disaster. Many scientists think that such a disaster caused the extinction of the dinosaurs and at least 70 percent of all other species alive at the time, including most of Earth's land plants. Geologists have since found iridium deposits in rocks of a similar age in more than 100 places worldwide. Scientists in the early 1990s identified a large impact crater in the Yucatán peninsula of central Mexico that is the same age as the iridium deposit found by Alvarez. It is 200 km (125 mi) wide and may have been caused by the same impact.
Etymology
Origin of iridium
1804; < Latin īrid-, stem of īris rainbow ( see iris) + -ium; so named from its iridescence when dissolved in hydrochloric acid
Vocabulary lists containing iridium
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
This includes valuable natural resources such as marble, gold, iridium, uranium and thorium and also possible deposits of oil and gas, with the information prepared by UK government officials, working for the Helmand reconstruction team.
From BBC ● Feb. 11, 2026
These include elevated levels of rare elements commonly associated with comets, such as platinum and iridium.
From Science Daily ● Jan. 1, 2026
"There is actually only one catalyst -- iridium oxide -- that remains stable."
From Science Daily ● Nov. 26, 2024
"Iridium is so rare that that scaling up global hydrogen production to the terawatt scale is estimated to require 40 years' worth of iridium," says co-first author Shuang Kong.
From Science Daily ● May 9, 2024
Then, I'll release hydrazine, very slowly, over the iridium catalyst, to turn it into N2 and H2.
From "The Martian" by Andy Weir
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
