Palladium, Rhodium, Ruthenium, Iridium, Osmium
Along with gold and silver, they are known as precious or noble metals. They occur as native alloys in placer deposits or, more commonly, in lode deposits associated with nickel and copper.
Nearly all of the world's supply of these metals are extracted from lode deposits in four countries--the Republic of South Africa, the U.S.S.R., Canada, and the United States. The Republic of South Africa is the only country that produces all six PGM in substantial quantities.
The Platinum group metals (PGM) comprise six closely related metals:
Palladium (symbol Pd), relatively rare, silvery white and relatively soft metal. Was discovered in 1804 by the British chemist William Hyde. Palladium is often alloyed with gold, to produce white gold.
Rhodium, brilliant silvery white metal (symbol Rh) derives its name from Greek rhodon -rose , was discovered in 1803 by the British chemist William Hyde Wollaston.
Pure rhodium is used as a plating finish for jewelry and silverware.
Ruthenium (symbol Ru), chemically unreactive, grayish-white metal. Was discovered in 1844 by the Russian chemist Karl Klaus.
Ruthenium and platinum alloys have a high resistance to wear and are used in the manufacture of jewelry, porcelain, etc.
Iridium (symbol Ir), white, brittle and extremely hard metal. The alloy, which contains about 10 percent iridium and 90% platinum, is much harder than pure platinum. Alloys containing larger percentages of iridium are used in making precision and standard instruments, surgical tools, pen points.
Osmium (symbol Os) bluish-white, brittle metal. Along with iridium, osmium is generally considered the most dense element. Was discovered in 1803 by the British chemist Smithson Tennant. Osmium and platinum alloys are used for standard weights and measures.