A bullion coin is a coin struck from refined precious metal (bullion) and kept as a store of value or an investment rather than used in day-to-day commerce. A bullion coin is distinguished by an explicit statement of weight (or mass) and fineness on the coin; this is because the weight and composition of coins intended for legal tender is specified in the coinage laws of the issuing nation, and therefore there is no need for an explicit statement on the coins themselves. The United Kingdom defines investment coins more specifically as coins that have been minted after 1800, have a purity of not less than 900 thousandths and are, or have been, legal tender in their country of origin. Under United States law, "coins" that fail the last of these requirements are not coins at all, and must be advertised as "rounds" instead. The American Eagle and Canadian Gold Maple Leaf series are the only coins available in gold, silver, platinum, and palladium.
Bullion coins are typically available in various weights. These are usually multiples or fractions of 1 troy ounce, but some bullion coins are produced in very limited quantities in kilograms or heavier.
Bullion coins sell for a premium over the market price of the metal on the commodities exchanges. Reasons include their comparative small size and the costs associated with manufacture, storage and distribution. The amount of the premium varies depending on the coin's type and weight and the precious metal. The premium also is affected by prevailing demand.
The ISO currency code for gold bullion is XAU. ISO 4217 includes codes not only for currencies, but also for precious metals (gold, silver, palladium and platinum, by definition expressed per one troy ounce, as compared to "1 USD") and certain other entities used in international finance, e.g. special drawing rights.