The American Gold Eagle is an official gold bullion coin of the United States. Authorized under the Gold Bullion Coin Act of 1985, it was first released by the United States Mint in 1986. Offered in 1/10 oz, 1/4 oz, 1/2 oz, and 1 oz denominations, these coins are guaranteed by the U.S. government to contain the stated amount of actual gold weight in troy ounces. By law, the gold must come from sources in America, with an additional alloy of silver and copper to produce a more wear-resistant coin of .9167 (22 karat, which had long been the crown gold English standard for gold coins, and before 1834, for American gold coins as well). It is authorized by the United States Congress and is backed by the United States Mint for weight and content. Gold Eagles are among the most highly collected coins in the world.