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Platinum is among the rarest and most expensive of the popular precious metals. Natural platinum is fairly impure. It is always associated with small amounts of other elements (gold, copper, nickel and iron) and commonly contains the rare metals platinum, palladium, rhodium, iridium, osmium and ruthenium.
Platinum was named ‘platina’, meaning ‘little silver,’ by the Spaniards when they first encountered it in Columbia. Platinum was regarded as an unwanted impurity in the silver they were mining and it was often discarded.
Note: Platinum is typically only used where a substitute is not available as it is very rare, or for prestige.
Platinum is both rarer and more expensive than gold. It does not oxidize at any temperature, it’s a good conductor of electricity and it is both malleable and ductile. It also has a very high melting temperature and it is unattached by any single acid (though soluble, like gold, in a mixture of hydrochloric and nitric acids). It is an incredibly stable mineral.
Platinum is a metallic white to silver-gray colour. Its streak is a shiny silver-gray. Crystals, if found, tent to be distorted cubes.
Platinum has a very high specific gravity. Pure platinum would have a SG of 21.4 however impurities commonly lower this number to a value of 14 to 19 units. For comparison, galena has a specific gravity of only 7.4 to 7.6.
Finally, a potentially diagnostic characteristic of platinum is that if it contains iron impurities then it will be slight attracted to magnetic fields. Most platinum contains traces of iron, but not all does.
Platinum in the Earth’s crust originates from ultra-mafic igneous rocks. It can therefore be associated with rocks like chromite and olivine.
In nature, pure platinum is unknown and well formed crystals are very rare. Platinum is typically found as nuggets and grains.
Before hard rock supplies came on line, nearly the entire world’s supply of platinum came from the Ural Mountains in Russia from placer deposits. The platinum would settle in the streams due to its high specific gravity.
At this time, platinum in quantity is limited to a few localities. 80% of the world’s current production comes from South Africa and the Sudbury Basin of Canada. Smaller reserves can be found in the United States, Zimbabwe and Australia.
Platinum is also attained through recycling. For example, in 1999 70 metric tons were recovered in this way.
Platinum arsenide, or sperrylite, is the only platinum ore of any significance besides native platinum. It was named after its discoverer Francis L. Sperry, who was a chemist of Sudbury, Ontario. Sperrylite is only found in abundance in Sudbury.
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