iridium

i·rid·i·um

I0230400 (ĭ-rĭd′ē-əm)n. Symbol Ir A very dense, 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 192.22; melting point 2,446°C; boiling point 4,428°C; specific gravity 22.562 (at 20°C); valence 2, 3, 4, 6. See Periodic Table.

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

iridium

(aɪˈrɪdɪəm; ɪˈrɪd-) n (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[C19: New Latin, from irido- + -ium; from its colourful appearance when dissolving in certain acids]

i•rid•i•um

(ɪˈrɪd i əm)

n. a precious metallic element resembling platinum: used in alloys. Symbol: Ir; at. wt.: 192.2; at. no.: 77; sp. gr.: 22.4 at 20°C. [1804; < Latin īrid-, s. of īris rainbow (see iris) + -ium²; so named from its iridescence when dissolved in hydrochloric acid]

i·rid·i·um

(ĭ-rĭd′ē-əm) Symbol Ir A rare, whitish-yellow element that is the most corrosion-resistant metal known. It is very dense, hard, and brittle. Iridium is used to make hard alloys of platinum for jewelry, pen points, and electrical contacts. Atomic number 77. See Periodic Table.Did You Know? In 1978 geologist Walter Alvarez found an unusually high concentration of the element iridium in a layer of clay. This layer formed at the time dinosaurs and many other organisms went extinct. The iridium deposits were a great surprise, since iridium is very rare at the Earth's surface. Most surface iridium is believed to come from outer space—from dust left over after meteors disintegrate in the atmosphere or smash into the Earth. Walter's father, the physicist Luis Alvarez, suggested that the iridium came from the impact of a meteor about 6 miles (10 kilometers) across. He argued that 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 acid rain for years, would have caused a worldwide ecological disaster. Many scientists think that such a disaster caused the extinction of dinosaurs and at least 70 percent of all other species alive at the time, including most of the Earth's land plants. Geologists have since found iridium deposits in rocks of a similar date in over 100 places worldwide. In the early 1990s, a large impact crater of the same age as the iridium deposits was identified in the Yucatan peninsula of central Mexico. It is 125 miles (200 kilometers) wide and may well have been caused by the impact hypothesized by Alvarez.

Thesaurus

Noun

1.

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

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