Platinum (Pt) is a chemical element in the periodic table that has the symbol Pt and atomic number 78. The Spaniards named the metal «platina», or little silver. A heavy, malleable, ductile, precious, gray-white transition metal, platinum is resistant to corrosion. Platinum is used in jewelry, laboratory equipment, electrical contacts, dentistry, and automobile emissions control devices. Applications: catalyst utilized in the catalytic converter, an optional component of the gasoline-fuelled automobile exhaust system; certain platinum-containing compounds are capable of intercalating into DNA and are chemotherapeutic agents owing to this capability; platinum resistance thermometers; electrodes for use in electrolysis.

The definition of a metre for a long time was based on the distance between two marks on a bar of a platinum-iridium alloy housed at the Bureau International des Poids et Mesures in Sevres, France. A platinum-iridium cylinder serves to this day as the standard of the kilogram and is housed in the same facility as the metre bar. Platinum is also used in the definition of the Standard hydrogen electrode.

Platinum is often found as native platinum and alloyed with iridium as platiniridium. The platinum arsenide, sperrylite, is a major source of platinum associated with nickel ores in the Sudbury Basin deposit. The rare sulfide mineral cooperite, (Pt,Pd,Ni)S, contains platinum along with palladium and nickel. Cooperite occurs in the Merensky Reef within the Bushveld complex, Transvaal, South Africa. Platinum, often accompanied by small amounts of other platinum family metals, occurs in alluvial placer deposits in the Witwatersrand of South Africa, Colombia, Ontario, the Ural Mountains in Russia, and in certain western American states.

From: http://en.wikipedia.org/ a.o.