- 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
Examples from the Web for iridium
Two years later, a Russian satellite crashed into a communications satellite owned by the company Iridium.Space Station’s Near Miss Underlines the Dangers of Debris in Space
March 27, 2012
To begin with metals, uranium melts at 1150 centigrade, and tungsten at 3370 and iridium at 2350.Pariah Planet
Iridium is always determined quantitatively by conversion into the metallic state.
Iridium sulphide, IrS, is obtained when the metal is ignited in sulphur vapour.
When pure, platinum is as soft as silver, but by the addition of iridium it becomes the hardest of metals.
In the top of the cap is a sapphire bearing, which rests on an iridium point projecting upward from the compass bowl.Lord Kelvin
- 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 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]
- A hard, brittle, corrosion-resistant metallic element, whose radioisotope is used in the treatment of tumors. Atomic number 77.
- 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.
A 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.