Like rhodium, palladium is largely used as a catalytic converter. As of January 2010, the price of this metal is estimated to be approximately USD424 per troy ounce (USD13,632 per kilogram). 4. Osmium - This element is represented by the symbol Os. Its atomic number is 76. It is found in nature as an alloy in platinum ores. The substances are identified through the spectrum they absorb or emit. This assay method has several types. These include absorption, fluorescence, X-ray, flame, visible, ultraviolet, infrared, photoemission, Mossbauer, nuclear magnetic resonance, and Raman. Again, the X-ray fluorescence (XRF) method is the modern assay method widely used today for analyzing precious metals, including (besides silver, gold, and platinum) rhenium, ruthenium, iridium, and palladium. Palladium: Least Dense Of The Platinum Group Metals Palladium is a rare precious metal characterized by its lustrous silvery-white appearance. It was discovered by the English chemist William Hyde Wollaston in London, England in 1803, along with his discovery (together with Smithson Tennant, another English chemist) of the other metals in the platinum group. To indicate the amount of gold present in, say, a piece of jewelry, the term "carat" is used. A necklace, for instance, that is 24 carats means that it is made of pure gold. While gold's price is determined through trading in the derivatives and gold markets, its daily benchmark price is provided in a procedure called the London Gold Fix. As an investment commodity, palladium may be bought in forms of bullion coins or bars. Palladium bullion coins are internationally recognized forms of currency and have the ISO codes XPD and 964. The first known palladium coins to be issued were those of Sierra Leone in 1966. The following year, Tonga started issuing theirs. Minting coins, whether gold or silver, always entails the risk of having the value of the metal used in the coin greater than the coin's face value. This is especially true in coins of low denomination. Because of this, there exists the possibility of some smelters taking gold or silver coins and melting these down for the scrap value of the precious metals.