Its value is determined by the worth of the metal rather than by its face value as money. To put it another way, bullion is valued based on the mass and purity of the metal used, instead of its artificial currency value. New sources of ore have been discovered and there also have been improvements in the mining and refining processes. Because of this, there exists the possibility of some smelters taking gold or silver coins and melting these down for the scrap value of the precious metals. A couple examples, in this regard, are worth mentioning here: US pennies have been made of copper-clad zinc since 1982, when they were before this time made of copper alloys; and British pennies were once made of 97% copper, but are now made of copper-plated steel. Of course, silver occurs natively, too. Some of the top silver-producing countries in the world are the United States, Canada, Peru, and Mexico. Fine silver, which has no less than 99.9% silver, is available commercially. Because of competing store-of-value and industrial demands, the price of silver has fluctuated considerably over the last century. What makes pure gold especially attractive is its bright yellow color and luster. These characteristics are maintained as gold is chemically unaffected by air or moisture. Here are some of the properties of gold: General: Chemical Symbol: Au Atomic Number: 79 Category (as an element): Transition Metal Group/ Period/ Block (in the Periodic Table): 11/ 6/ d Atomic Weight: 196.966569(4) g. 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. 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. Following is a list of some of the properties of ruthenium: General: Chemical Symbol: Ru Atomic Number: 44 Category (as an element): Transition Metal Group/ Period/ Block (in the Periodic Table): 8/ 5/ d Atomic Weight: 101.07 g.mol-1 Electron Configuration: [Kr] 4d7 5s1 Physical: Density (near room temperature): 12.45 g.