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[ih-rid-ee-uh m, ahy-rid-] /ɪˈrɪd i əm, aɪˈrɪd-/
noun, Chemistry.
a precious metallic element resembling platinum: used in platinum alloys and for the points of gold pens. Symbol: Ir; atomic weight: 192.2; atomic number: 77; specific gravity: 22.4 at 20°C.
Origin of iridium
1804; < Latin īrid-, stem of īris rainbow (see iris) + -ium; so named from its iridescence when dissolved in hydrochloric acid Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for iridium


/aɪˈrɪdɪəm; ɪˈrɪd-/
a very hard inert yellowish-white transition element that is the most corrosion-resistant metal known. It occurs in platinum ores and is used as an alloy with platinum. Symbol: Ir; atomic no: 77; atomic wt: 192.22; valency: 3 or 4; relative density: 22.42; melting pt: 2447°C; boiling pt: 4428°C
Word Origin
C19: New Latin, from irido- + -ium; from its colourful appearance when dissolving in certain acids
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Word Origin and History for iridium

1804, Modern Latin, coined by its discoverer, English chemist Smithson Tennant (1761-1815) from Greek iris (genitive iridos) "rainbow;" so called for "the striking variety of colours which it gives while dissolving in marine acid" [Tennant]

Online Etymology Dictionary, © 2010 Douglas Harper
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iridium in Medicine

iridium i·rid·i·um (ĭ-rĭd'ē-əm)
Symbol Ir
A hard, brittle, corrosion-resistant metallic element. Atomic number 77; atomic weight 192.2; melting point 2,450°C; boiling point 4,430°C; specific gravity 22.42 (at 17°C); valence 3, 4.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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iridium in Science
Symbol Ir
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. See Periodic Table.

Our Living Language  : 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.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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