Bullion coins

While obsolete gold coins are primarily collected for their numismatic value, gold bullion coins today derive their value from the metal (gold) content — and as such are viewed by some investors as a "hedge" against inflation or a store of value. South Africa introduced the Krugerrand in 1967 to cater to this market; this was the reason for its convenient and memorable gold content — exactly one troy ounce. It was the first modern, low-premium (i.e. priced only slightly above the bullion value of the gold) bullion gold coin. Bullion coins are also produced in fractions of an ounce – typically half ounce, quarter ounce, and one-tenth ounce. Bullion coins do not carry a meaningful face value, as their value is mainly dictated by their troy weight, the current market price of the precious metal and the prevailing premium that market wishes to pay. (If a face value is minted on the coin, it is done so in order to bestow legal tender status on a coin, which generally makes it easier to import or export across national borders. The face value is nearly always significantly less than the actual value of the coin.) Gold has an international currency code of XAU under ISO 4217.

Gold bullion coins usually come in 1 oz, 1/2 oz, 1/4 oz, 1/10 and 1/20 oz. sizes. Most countries have one design that remains constant each year; others have variations each year, and in most cases each coin is dated. A 1/10th oz bullion coin is about the same size as a U.S. dime. A 1 oz. gold bullion coin is about the size of a U.S. half dollar.

Krugerrand

American Gold Eagle

Mexican Gold Libertad

Other gold bullion coins, many named after their design features, include:

 Counterfeits

For most of history, coins were valued based on the precious metal they contain. Whether or not a coin was actually made by the party that it is claimed to be made by was of secondary importance compared to whether or not it contains the correct amount of metal, that is, right weight and fineness (purity). Genuine appearance was simply a convenient shortcut to avoid time-consuming tests in everyday transactions.

Unlike silver, gold is denser than almost all other metals, hence whether something is made of gold is extremely hard to fake. Simple determination of weight and volume should be sufficient. A coin that is the right size but is not gold, or has too much base metal, will be "light"; alternately, a coin that weighs right will be somewhat larger. (Platinum was unknown in ancient times; platinum is denser than gold, but since the price of platinum is usually much higher than that of gold, making a fake coin out of platinum would make no sense. In theory, fake coins could be made of uranium, but this does not appear to be a practical problem.One element that just about the same density as gold is tungsten. Alloying gold with tungsten would not work for several reasons but a coin with a tungsten center and gold all around it could not be detected as counterfeit by density measurement alone.

An old practice to test whether a gold coin was counterfeit was to bite down on it. Since pure gold is relatively soft any base metals mixed with the gold to lessen its value will also harden the coin, and so make it harder to bite on.

The majority of bullion counterfeits (of all types) are rare, and fairly easy to detect when comparing their weights, colors and sizes to authentic pieces. This is because the cost of reproducing any given coin precisely can easily exceed the market value of the originals.

 Numismatic fake samples

There are well made counterfeit gold coins in circulation. For example, the St. Gaudens Double Eagle omega counterfeit is infamous for its complexity[2] and has fooled many numismatics experts. It is a high relief business strike, and due to the extensive wear on the die, these coins were not made for many years.
Another example is the US $20 gold coin ("double eagle"), which has raised lettering around its rim. If the coin is uncirculated, the letters will be flat on top. If slightly rounded, and the coin is uncirculated, it is a counterfeit. However, some counterfeits do not have this defect. There are other counterfeit double eagles in which the gold and copper alloy was not thoroughly mixed. These counterfeits will have a slightly mottled appearance.