The Eight Precious Metals Considered Noble Metals Most metallic chemical elements are known to easily oxidize and corrode, especially at high temperatures. Metals that have excellent resistance to oxidation and corrosion, even at high temperatures, are called noble metals. While there is no strict definition for this group of metals, it usually includes those that are extremely rare. Before the turn of the 20th century, countries that were still on silver standard started pegging their monetary units to the gold standard of either the United States or the United Kingdom. For example, Mexico, the Philippines, and Japan pegged their respective silver units to the U.S. dollar at fifty cents. The decisions of these gold-producing countries to mint their own bullion coins were most likely inspired by the success of the Krugerrand in its role as a vehicle for promoting the South African gold to the international market. As of 2008, about 1.3 million kilograms of South African gold, contained in Krugerrand coins, have been sold. Placer mining may be done through a number of tunneling procedures into riverbeds. There also are the open-cast mining and hydraulic mining. In the former, placer mining is done by open-pit; in the latter, water pressure is used for excavation. 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. New sources of ore have been discovered and there also have been improvements in the mining and refining processes. These two factors may cause the values of gold, silver, and the other precious metals to diminish. Also, the "precious" qualification of a metal is determined by the market value or high demand. Owning a gold certificate: A gold investor may opt to hold on to a gold certificate rather than store the physical gold bullion. The gold certificate allows the investor to buy and sell the security and do away with the many difficulties associated with the actual gold's transfer. Trading in Gold Exchange-Traded Funds (GETFs): Trading in GETFs is like trading shares in, say, the New York Stock Exchange or the London Stock Exchange.