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The eagle was a United States $10 gold coin issued by the United States Mint from 1792 to 1933.
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base-units of denomination used for circulating coinage in the United States prior to 1933, the year when gold was withdrawn from circulation. 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 base-unit of denomination served as the basis of the quarter eagle ($2.50), half eagle ($5), eagle ($10), and double eagle ($20) coins.
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. In this regard the United States followed long-standing European practice of different base-unit denominations for different precious and semi-precious metals. In the United States, the cent was the base-unit of denomination in copper. The dime and dollar were the base-units of denomination in silver. The eagle was the base-unit of denomination in gold although, unlike "cent", "dime" (or "disme"), and "dollar", gold coins never specified their denomination in units of "eagles". Thus, a double eagle showed its value as "twenty dollars" rather than "two eagles".
The United States' circulating eagle denomination from the late 18th century through to the first third of the 20th century should not be confused with the American Eagle bullion coins which are manufactured from silver or gold (since 1986), platinum (since 1997), or palladium (since 2017).
Gold eagles were issued for circulation by the United States Mint from 1795–1933, half eagles from 1795–1929, quarter eagles from 1796–1929, and double eagles from 1850–1933, with occasional production gaps for each type. Except for the double eagle, the diameters of all these denominations were decreased over time. The following table presents the diameters of each of the denominations, in millimeters (mm), according to the first year that diameter was used:
|Year||Quarter Eagle||Half Eagle||Eagle||Double Eagle|
|1795||--||25.0 mm||33.0 mm||--|
|1829||18.2 mm||23.8 mm||--||--|
|1840||18.0 mm||21.6 mm||--||--|
Originally the purity of all circulating gold coins in the United States was eleven twelfths pure gold (the same 22 karats level as English crown gold) and one twelfth alloy. Under U.S. law, the alloy was composed only of silver and copper, with silver limited to no more than half of the alloy by weight. Thus, U.S. gold coins had 22/24 (22 kt or 91.667%) pure gold, at most 1/24 (0–4.167%) silver, with the remaining fraction, (4.167–8.333%), copper. 
The weight of circulating, standard gold, $10 eagles was set at 270 grains (17.5 g), half eagles at 135 grains (8.75 g), quarter eagles at 67.5 grains (4.37 g). This resulted in the $10 eagle containing 0.5156 troy ounces (16.04 g) of pure gold.
In 1834, the mint's 15:1 legal valuation of gold to silver (i.e. 15 weight units of silver and 1 weight unit of gold have the same legal monetary value) was changed to 16:1, and the metal weight-content standards for both gold and silver coins were changed, because at the old value ratio and weight content, it was profitable to export and melt U.S gold coins. As a result, the specification for standard gold was lowered from 22 karat (.9167 fine) to .8992 fine (21.58 kt).
In 1837 a small change in the fineness of the gold (increased to exactly .900 fine) was made, and the alloy (now 10% of the coin's weight) was again legally defined as silver and copper, with silver capped at no more than half.  (i.e. 5% of total coin weight) The new Coinage Act of 1837 standard for the $10 eagle was 258 grains (16.7 g) of .900 fine gold, giving pure gold content of 0.48375 ozt = 15.03 g, with other coins proportionately sized.
Between 1838 and 1840, the silver content was reduced to zero—the eagle in 1838, half eagle in 1839, and quarter eagle in 1840,  —resulting in U.S. gold coins being 90% gold and 10% copper. Using only copper as the alloy in gold coins matched longstanding English practice (see crown gold).  The new standard would be used for all circulating gold coins until U.S. gold coin circulation was halted in 1933.
As part of its Modern United States commemorative coins program the United States mint has issued several commemorative eagle coins. In 1984, an eagle was issued to commemorate the Summer Olympics, and another eagle was issued in 2003 to commemorate the Wright brothers first flight at Kitty Hawk. The pre-1933 .900 fine gold standard was restored, this would also be used in half-eagle gold commemoratives as well. The coins would be identical in fineness and size to their pre-1933 counterparts of the same face value. In 2000 a unique eagle, the Library of Congress bimetallic eagle, was issued commemorating the Library of Congress; it consisted of equal weights of an approximately 1/4 oz .9995 fine platinum core and a .900 fine gold outer ring.
Coins of the United States dollar were first minted in 1792. New coins have been produced annually and they make up a valuable aspect of the United States currency system. Today, circulating coins exist in denominations of 1¢, 5¢, 10¢, 25¢, 50¢, and $1.00. Also minted are bullion and commemorative coins. All of these are produced by the United States Mint. The coins are then sold to Federal Reserve Banks which in turn are responsible for putting coins into circulation and withdrawing them as demanded by the country's economy.
A nickel is a five-cent coin struck by the United States Mint. Composed of cupronickel, the piece has been issued since 1866. Its diameter is 0.835 inches (21.21 mm) and its thickness is 0.077 inches (1.95 mm).
The dime, in United States usage, is a ten-cent coin, one tenth of a United States dollar, labeled formally as "one dime". The denomination was first authorized by the Coinage Act of 1792.
The Coinage Act of 1792, passed by the United States Congress on April 2, 1792, created the United States dollar as the country's standard unit of money, established the United States Mint, and regulated the coinage of the United States. This act established the silver dollar as the unit of money in the United States, declared it to be lawful tender, and created a decimal system for U.S. currency.
The half dime, or half disme, was a silver coin, valued at five cents, formerly minted in the United States.
The fineness of a precious metal object represents the weight of fine metal therein, in proportion to the total weight which includes alloying base metals and any impurities. Alloy metals are added to increase hardness and durability of coins and jewelry, alter colors, decrease the cost per weight, or avoid the cost of high-purity refinement. For example, copper is added to the precious metal silver to make a more durable alloy for use in coins, housewares and jewelry. Coin silver, which was used for making silver coins in the past, contains 90% silver and 10% copper, by mass. Sterling silver contains 92.5% silver and 7.5% of other metals, usually copper, by mass.
The American twenty-cent piece is a coin struck from 1875 to 1878, but only for collectors in the final two years. Proposed by Nevada Senator John P. Jones, it proved a failure due to confusion with the quarter, to which it was close in both size and value.
The Flowing Hair dollar was the first dollar coin issued by the United States federal government. The coin was minted in 1794 and 1795; its size and weight were based on the Spanish dollar, which was popular in trade throughout the Americas.
This glossary of numismatics is a list of definitions of terms and concepts relevant to numismatics and coin collecting, as well as sub-fields and related disciplines, with concise explanations for the beginner or professional.
The quarter eagle was a gold coin issued by the United States with a denomination of two hundred and fifty cents, or two dollars and fifty cents. It was given its name in the Coinage Act of 1792, as a derivation from the US ten-dollar eagle coin.
The three-dollar piece was a gold coin produced by the United States Bureau of the Mint from 1854 to 1889. Authorized by the Act of February 21, 1853, the coin was designed by Mint Chief Engraver James B. Longacre. The obverse bears a representation of Lady Liberty wearing a headdress of a Native American princess and the reverse a wreath of corn, wheat, cotton, and tobacco.
The half eagle is a United States coin that was produced for circulation from 1795 to 1929 and in commemorative and bullion coins since 1983. Composed almost entirely of gold, its face value of five dollars is half that of the eagle coin. Production of the half eagle was authorized by the Coinage Act of 1792, and it was the first gold coin minted by the United States.
"Draped Bust" was the name given to a design of United States coins. It appeared on much of the regular-issue copper and silver United States coinage, 1796–1807. It was designed by engraver Robert Scot.
The United States Mint has minted over 20 different kinds of coins, of many different sizes. Often, it is difficult for people to get a grasp of what much of the historical coinage looked like, at least in relation to modern circulating coins. This chart shows all of the coin types, and their sizes, grouped by coins of similar size and by general composition.
The United States dollar is the official currency of the United States and several other countries. The Coinage Act of 1792 introduced the U.S. dollar at par with the Spanish silver dollar, divided it into 100 cents, and authorized the minting of coins denominated in dollars and cents. U.S. banknotes are issued in the form of Federal Reserve Notes, popularly called greenbacks due to their predominantly green color.
The Turban Head eagle, also known as the Capped Bust eagle, was a ten-dollar gold piece, or eagle, struck by the United States Mint from 1795 to 1804. The piece was designed by Robert Scot, and was the first in the eagle series, which continued until the Mint ceased striking gold coins for circulation in 1933. The common name is a misnomer; Liberty does not wear a turban but a cap, believed by some to be a pileus or Phrygian cap : her hair twisting around the headgear makes it resemble a turban.
The numismatic history of the United States began with Colonial coins such as the pine tree shilling and paper money; most notably the foreign but widely accepted Spanish piece of eight, ultimately descended from the Joachimsthaler and the direct ancestor of the U.S. Dollar.
The copper-nickel three-cent piece, often called a three-cent nickel piece or three-cent nickel, was designed by US Mint Chief Engraver James B. Longacre and struck by the United States Bureau of the Mint from 1865 to 1889. It was initially popular, but its place in commerce was supplanted by the five-cent piece, or nickel.
The three-cent silver, also known as the three-cent piece in silver or trime, was struck by the Mint of the United States for circulation from 1851 to 1872, and as a proof coin in 1873. Designed by the Mint's chief engraver, James B. Longacre, it circulated well while other silver coinage was being hoarded and melted, but once that problem was addressed, became less used. It was abolished by Congress with the Coinage Act of 1873.
The Capped Bust coinage of the United States consisted of a half dime, dime, quarter and half dollar.