In this regard the United States followed long-standing European practice of different base-unit denominations for different precious and semi-precious metals. With the exceptions of the gold dollar coin, the gold three-dollar coin, the three-cent nickel, and the five-cent nickel, the unit of denomination of coinage prior to 1933 was conceptually linked to the precious or semi-precious metal that constituted a majority of the alloy used in that coin. The eagle base-unit of denomination served as the basis of the quarter eagle ($2.50), half eagle ($5), eagle ($10), and double eagle ($20) coins.
These five main base-units of denomination were the mill, the cent, the dime, the dollar, and the eagle, where a cent is 10 mills, a dime is 10 cents, a dollar is 10 dimes, and an eagle is 10 dollars. The eagle was the largest of the five main decimal base-units of denomination used for circulating coinage in the United States prior to 1933, the year when gold was withdrawn from circulation. The eagle was a United States $10 gold coin issued by the United States Mint from 1795 to 1933. First two design types of the eagle coin with Turban Head obverse ( Liberty's hair wrapped around a Phrygian cap) and both small eagle (top) and heraldic eagle (bottom) reverses.
