This is lower by about 77 million troy ounces when compared with the annual mine production of gold, and even much lower - by about 547 million troy ounces - when compared with the yearly silver mine production. Platinum is traded on the London Stock Exchange (as ETF, under the ticker symbol LSE: PHPT) and on the New York Mercantile Exchange. For example, it is obtained as a white inert metal from platinum ores, which is quite difficult to fuse. The main source of this precious metal is in South Africa, which accounts for about 80 percent of the total world exports. Estimates place the annual production of rhodium at only about 25 tons. Some of the properties of rhodium are listed below. Distribution of these were as follows: electrochemical uses (1,100 kilograms); electrical uses (780 kilograms); for catalysis (750 kilograms); and other applications (1,100 kilograms). Iridium is found at highest concentrations within the Earth's crust in three specific types of geologic structures: in impact craters, in igneous deposits, and in deposits reworked from either of the first two. It is mostly found in platinum ores and often used in platinum alloys as a catalyst. Its two main physical characteristics refer to its hardness as a metal and to its silvery-white color. The former characteristic makes ruthenium ideal for use in making wear-resistance electrical contacts. The price of this precious metal as of January 2010 is estimated to be about USD173 per troy ounce (USD5,562 per kilogram). The United States adopted the gold specie standard "de jure" (by law) in 1873, using the American Gold Eagle as unit. Gold Exchange Standard: In this gold standard, only the circulation of coins minted from lesser valuable metals (such as silver) may be involved. The authorities, however, will have undertaken a fixed exchange rate with a country that's on the gold standard. Cupellation: This technique is considered the most exact, elaborate, and destructive method of assay and is best suited for gold bullion or stock. Also called fire assay, the method involves treating ores or alloyed metals under high temperatures and carefully controlled operations to separate gold from base metals (copper, zinc, or lead), which may be present in the ore.