The Australian Platinum Koala: The Australian Platinum Koala bullion coins were first released in 1988 by the Perth Mint, the oldest currently operating mint in Australia. The coin comes in 1 oz. variety, with a face value of AD100. As with most other bullion coins, this value is much lower than the coin's bullion value. All transition metals, these six elements are collectively referred to as the "platinum group metals". These precious metals tend to occur with one another in mineral deposits. Likewise, they are alike in both chemical and physical properties. In the order of their arrangement in the periodic table, the six metallic elements of the platinum group are ruthenium, rhodium, palladium, osmium, iridium, and platinum. mol-1 (third) The principal use of rhodium is as a catalytic converter in automotive vehicles, which reduces the toxicity of engine emissions by converting these into less harmful gases. Rhodium is likewise used in jewelry, such as when it is electroplated on platinum, sterling silver, or white gold (called rhodium flashing) to strengthen the metal or give it a reflective surface. Gram and troy weight are the units of measurement used for gold. 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. Compass bearings, balances and fountain pen tips, on the other hand, are made from osmium-iridium alloys. Again, iridium is the most corrosive resistant precious metal known. Coupled with its resistance to extremely high temperatures, this special characteristic makes iridium ideal for use in certain parts of aircraft engines. Palladium - William Hyde Wollaston, an English chemist and physicist, discovered palladium in 1803 in samples of platinum ore obtained from South America. He named it after the asteroid Pallas, which was discovered on March 28 the year before. 3. Osmium - Smithson Tennant, an English chemist, discovered osmium in 1803 from the residues of platinum ores that were dissolved in nitro-hydrochloric acid.