Entering in a Contract For Difference (CFD): Some of the noted financial services firms, especially those in the United Kingdom, provide Contract for Difference (CFD). In this gold investment vehicle, two parties (a "buyer" and a "seller") enter into a contract, in which the seller agrees to pay the buyer the difference between the current value of gold and its value at contract time. The Perth Mint Certificate Programme, which is fully guaranteed by the Government of Western Australia, is the only silver certificate program in the world that is guaranteed by a national government. Trading in Exchange-Traded Funds (ETFs): An investor can have an easy way of gaining exposure to the price of silver through an ETF. Known to be one of the rarest precious metals in the Earth's crust, rhenium has an average concentration of 1 part per billion. It is obtained mainly as a by-product of the refinement of two other chemical elements - copper and molybdenum. Rhenium was discovered as a trace element in the mineral columbite and in platinum ores. Thus, metals that are labeled "precious" are also considered noble metals (note, however, that noble metals are not necessarily precious metals). There are nine known precious metals - gold, platinum, iridium, palladium, osmium, silver, rhodium, ruthenium, and rhenium. With the exception of the latter, all are considered noble metals. The Canadian Platinum Maple Leaf: The Canadian Platinum Maple Leaf bullion coins were issued from 1988 until 2002 by the Royal Canadian Mint (RCM). They were offered in four varieties: 1/10 oz. coin (with a face value (FV) of CD5), 1/4 oz. coin (FV: CD10), 1/2 oz. coin (FV: CD20), and 1 oz. coin (FV: CD50). As a non-destructive assay method, XRF can identify various elements in a substance (in fact, even in powder and liquid ones) within a few minutes. One of the most important aspects in any of the assay methods pertains to the accurate determination of the composition of a substance at various points in the process.