Iridium is the chemical element with atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C. Although only certain molten salts and halogens are corrosive to solid iridium, finely divided iridium dust is much more reactive and can even be flammable. Iridium was discovered in 1803 by Smithson Tennant among insoluble impurities in natural platinum from South America. It is one of the rarest elements in the Earth's crust, with annual production and consumption of only three tonnes. However, iridium does find a number of specialized industrial and scientific applications. Iridium is employed when high corrosion resistance and high temperatures are needed, as in spark plugs, crucibles for recrystallization of semiconductors at high temperatures, electrodes for the production of chlorine in the chloralkali process, and radioisotope thermoelectric generators used in unmanned spacecraft. Iridium is found in meteorites with an abundance much higher than its average abundance in the Earth's crust. It is thought that due to the high density and siderophilic ("iron-loving") character of iridium, most of the iridium on Earth is found in the inner core of the planet.

Read the rest of this article: http://en.wikipedia.org/wiki/Iridium

_______________________________ Today's selected anniversaries:

1734:

A black slave known as Marie-Joseph Angélique, after having been convicted of setting the fire that destroyed much of Montreal, was tortured and then hanged in New France. http://en.wikipedia.org/wiki/Marie-Joseph_Ang%C3%A9lique

1813:

Peninsular War: The Marquess of Wellington's combined British, Portuguese, and Spanish allied army defeated the French near Vitoria, Spain. http://en.wikipedia.org/wiki/Battle_of_Vitoria

1826:

Greek War of Independence: A combined Egyptian and Ottoman army began their invasion of the Mani Peninsula, but they were initially held off by the Maniots at the fortifications of Vergas. http://en.wikipedia.org/wiki/Ottoman%E2%80%93Egyptian_Invasion_of_Mani

1948:

The Manchester Small-Scale Experimental Machine , the world's first stored-program computer, ran its first computer program. http://en.wikipedia.org/wiki/Manchester_Small-Scale_Experimental_Machine

1973:

The U.S. Supreme Court delivered its decision in the landmark case Miller v. California, establishing the "Miller test" for determining what is obscene material. http://en.wikipedia.org/wiki/Miller_v._California

_____________________________ Wiktionary's word of the day:

spinet (n): A short, compact harpsichord http://en.wiktionary.org/wiki/spinet

___________________________ Wikiquote quote of the day:

Every natural fact is a symbol of some spiritual fact. --Ralph Waldo Emerson http://en.wikiquote.org/wiki/Ralph_Waldo_Emerson