A Double Eagle is a gold coin of the United States with a denomination of $20. (Its gold content of 0.9675 troy oz was worth $20 at the then official price of $20.67/oz). The coins are made from a 90% gold (0.900 fine = 21.6 kt) and 10% copper alloy.
Although the “eagle”-based nomenclature for gold U.S. coinage is often assumed to be a nickname, the “eagle”, “half-eagle” and “quarter-eagle” were specifically given these names in the Act of Congress that originally authorized them («An Act establishing a Mint, and regulating Coins of the United States», section 9, April 2, 1792). Likewise, the Double Eagle was specifically created as such by name («An Act to authorize the Coinage of Gold Dollars and Double Eagles», title and section 1, March 3, 1849).
Peter Swanston of the London Mint Office holds a “Double Eagle” gold twenty dollar coin at Goldsmith's Hall on March 2, 2012 in London, England. Nearly half a million of these coins were originally minted in the midst of the Great Depression in the US. Only 13 are known today after the rest were melted down before they ever left the US Mint, sacrificed as part of a strategy to stabalise the American economy. In 2002 a Double Eagle sold at auction for $7.6 million. (Photo by Peter Macdiarmid/Getty Images)