iridium

i·rid·i·um  (-rd-m)

n. Symbol Ir

A very hard and brittle, exceptionally corrosion-resistant, whitish-yellow metallic element occurring in platinum ores and used principally to harden platinum and in high-temperature materials, electrical contacts, and wear-resistant bearings. Atomic number 77; atomic weight 192.2; melting point 2,446°C; boiling point 4,428°C; specific gravity 22.562 (at 20°C); valence 2, 3, 4, 6. See Table at element.

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[From Latin ris, rid-, rainbow (from the colors produced by dissolving it in hydrochloric acid); see irido- + -ium.]

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iridium [aɪˈrɪdɪəm ɪˈrɪd-]

n

(Chemistry / Elements & Compounds) 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

[New Latin, from irido- + -ium; from its colourful appearance when dissolving in certain acids]

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iridium  (-rd-m)

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.

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.

Thesaurus

Noun

1.

iridium - a heavy brittle metallic element of the platinum group; used in alloys; occurs in natural alloys with platinum or osmium atomic number 77, Ir metal, metallic element - any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.

Translations

iridium [ɪˈrɪdɪəm] N → iridio m