Bullion coins minted from platinum include the Manx Noble (minted from 1983 to 1989), the Canadian Platinum Maple Leaf (1988 to 1999), the Australian Platinum Koala (1988 to the present), the Mexican Libertad (1989 only), and the American Platinum Eagle (1997 to the present). The Chinese Platinum Panda were minted in three periods: from 1988 to 1990, 1993 to 1997, and lastly from 2002 to 2005. Safety Issues Concerning Precious Metals The metallic chemical elements collectively known as precious metals are called as such because of their extreme rarity and high economic value. Precious metals occur naturally or are by-products of the processing of other less rare metals. In order of increasing mass abundance (parts per billion), the precious metals are rhenium, rhodium, iridium, ruthenium, osmium, gold, platinum, palladium, and silver. Gold Bullion Securities, the first GETF introduced (in 2003, on the Australian Stock Exchange), stood for 1/10 of an ounce of gold. GETFs are a good means of gaining exposure to the price of gold, minus the inconvenience of storage. Trading in GETFs involves payment of commission and storage fee (charged on an annual basis). Throughout history, gold has served as a measure of value and a symbol of wealth. It is one of the coinage metals (along with silver and copper). It is used, customarily and legally, as a means of payment or a medium of exchange. 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. Other uses of rhenium are as follows: 1. As catalysts in making lead-free, high-octane gasoline. 2. As filaments in making ion gauges, mass spectrographs, and photoflash lamps. 3. As electrical contact materials, due to its high resistance to arc corrosion and wear. 4. As catalysts for hydrogenation of fine chemicals, because of its high resistance to chemical poisoning from phosphorus, sulfur, and nitrogen. mol-1 (first), 1740 kJ.mol-1 (second), 2997 kJ.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.