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.
LIBERTY HEAD DOUBLE EAGLE
Due to the less desirable artwork and therefore lower demand, Liberty Coronet double eagle $20 gold pieces are less often encountered, and the common subtype commands less than the St. Gaudens’ type. In 1866, the motto “In God We Trust” was added to the Liberty Coronet double eagle creating a second subtype. In 1877, the coin’s denomination design on the reverse was changed from “Twenty D” to “Twenty Dollars” creating a third and final subtype for the series. An 1879 pattern coin was made for the quintuple stella using a design combining features of the Liberty head double eagle and stella pattern coin and using the same alloy as the stella (90 parts gold, 3 parts silver, and 7 parts copper). However this coin was suddenly stolen in July 2008 by two thieves. The robbery was planned a year after the coin was sold. The criminals have still not been caught and the locations of these men are unknown.
Article Source: en.wikipedia.org