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. There are three placer mining methods used to mine placer gold: Gold Panning: This method, which involves the use of a pan, is the oldest and simplest way to extract gold from a placer deposit. In this method, mined ore is placed in a large pan (made either of plastic or metal) and poured with a liberal amount of water; it is then agitated. The ranking appears different when the estimated world market prices, per troy ounce, of these nine precious metals are considered (estimates as of January 2010): 1st: Rhodium - USD2,750 2nd: Platinum - USD1,555 3rd: Gold - USD1,131 4th: Palladium - USD424 5th: Iridium - USD408 6th: Osmium - USD380 7th: Rhenium - USD194 8th: Ruthenium - USD173 9th: Silver - USD18 Of the nine precious metals, gold and silver are the best known. Their market values are determined by their inherent precious metal contents. As such bullion coins are mainly kept as investments or stores of value. Most of the bullion coins available are made from silver or gold. A few also come in platinum though, including the American Platinum Eagle, the Canadian Platinum Maple Leaf, the Australian Platinum Koala, and the Manx Noble. Its principal use is for electrical purposes, mainly because of its density and its high resistance to corrosion even at extremely high temperatures. Iridium is considered the fourth least abundant element in the Earth's crust, after rhenium, ruthenium, and rhodium. Its price is estimated to be about USD408 per troy ounce (USD13,117 per kilogram) as of January 2010. To determine the precious metal content in an item, certain non-destructive assay techniques are used. Two examples are the touchstone method (a very old assay method) and the X-ray fluorescence method (the modern, non-destructive assay method). While these assay methods are suited for finished goods (again because they are non-destructive), three other methods are more suited for raw precious metals: Titration: This assay method is one of the most widely used laboratory technique, which involves the analysis and determination of unknown concentration of a given reactant.