|Value||100 US Dollars|
|Composition||90% Au |
|Design||Liberty holding the caduceus and a branch (fantasy coin shown)|
|Designer||George T. Morgan|
|Design||Eagle (fantasy coin shown)|
|Designer||George T. Morgan|
The Union was a proposed $100 coin of the United States dollar. It was canceled before any pattern coins could be minted.
In 1854, San Francisco businessmen sent a petition to Secretary of the Treasury James Guthrie for a $50 coin to be struck due to the fact that no banknotes of any denomination circulated in California. Guthrie responded to the petition by introducing a measure to produce gold $50 and $100 coins, called half union and union, respectively. Although the measure passed the Senate on June 16, 1854, it was ultimately defeated in the House. 
United States Mint engraver George T. Morgan made sketches of a possible design for a $100 coin in 1876, should the half union ever be a success. When the mint concluded that the half union (a gold coin weighing about 2.7 troy ounces or 83.6 grams) was infeasible, the idea of a union coin was discarded and forgotten.
Around 2005, Morgan's original sketches were discovered and published so the numismatic community could see what could have been. Private mints have since struck fantasy pieces of Morgan's design for collectors, in both silver and gold. 
The $100 denomination has been produced by the US Mint since 1997 in the form of the American Platinum Eagle bullion coin.  The bullion American Liberty union of 2015, 2019, and 2021 as well as the proof American Liberty 225th Anniversary union of 2017 were struck in 24 karat gold.  
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.
The United States Mint is a bureau of the Department of the Treasury responsible for producing coinage for the United States to conduct its trade and commerce, as well as controlling the movement of bullion. It does not produce paper money; that responsibility belongs to the Bureau of Engraving and Printing. The first United States Mint was created in Philadelphia in 1792, and soon joined by other centers, whose coins were identified by their own mint marks. There are currently four active coin-producing mints: Philadelphia, Denver, San Francisco, and West Point.
The United States Mint has minted numerous commemorative coins to commemorate persons, places, events, and institutions since 1848. Many of these coins are not intended for general circulation, but are still legal tender. The mint also produces commemorative medals, which are similar to coins but do not have a face value, and therefore are not legal tender.
The dollar coin is a United States coin with a face value of one United States dollar. Dollar coins have been minted in the United States in gold, silver, and base metal versions. Dollar coins were first minted in the United States in 1794.
The eagle was a United States $10 gold coin issued by the United States Mint from 1792 to 1933.
The American Silver Eagle is the official silver bullion coin of the United States.
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. Because the term "eagle" also is the official United States designation for pre-1933 ten dollars gold coins, the weight of the bullion coin is typically used when describing American Gold Eagles to avoid confusion. This is particularly true with the 1/4-oz American Gold Eagle, which has a marked face value of ten dollars.
The American Platinum Eagle is the official platinum bullion coin of the United States. In 1995, Director of the United States Mint Philip N. Diehl, American Numismatic Association President David L. Ganz, and Platinum Guild International Executive Director Jacques Luben began the legislative process of creating the Platinum Eagle. After over two years of work, the 99.95% fine platinum coins were released by the United States Mint in 1⁄10, 1⁄4, 1⁄2 and 1 troy oz denominations. In late 2008, the fractional denominations were discontinued, leaving only the one ounce denomination. The Platinum Eagle is authorized by the United States Congress, and is backed by the United States Mint for weight, content, and purity.
The West Point Mint is a U.S. Mint production and depository facility erected in 1937 near the U.S. Military Academy in West Point, New York, United States. As of 2019 the mint holds 22% of the United States' gold reserves, or approximately 54 million ounces. The mint at West Point is second only to the gold reserves held in secure storage at Fort Knox. Originally, the West Point Mint was called the West Point Bullion Depository. At one point it had the highest concentration of silver of any U.S. mint facility, and for 12 years produced circulating Lincoln cents. It has since minted mostly commemorative coins and stored gold.
The quarter eagle was a gold coin issued by the United States with a value 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 American Buffalo, also known as a gold buffalo, is a 24-karat bullion coin first offered for sale by the United States Mint in 2006. The coin follows the design of the Indian Head nickel and has gained its nickname from the American Bison on the reverse side of the design. This was the first time the United States Government minted pure (.9999) 24-karat gold coins for the public. The coin contains one-troy ounce (31.1g) of pure gold and has a legal tender (face) value of US$50. Due to a combination of the coin's popularity and the increase in the price of gold the coin's value has increased considerably. The initial 2006 U.S. Mint price of the proof coin was $800. In 2007 the price was $899.95, $1,410 in 2009, and $2,010 in 2011.
The gold dollar or gold one-dollar piece is a gold coin that was struck as a regular issue by the United States Bureau of the Mint from 1849 to 1889. The coin had three types over its lifetime, all designed by Mint Chief Engraver James B. Longacre. The Type 1 issue has the smallest diameter of any United States coin minted to date.
The America the Beautiful quarters were a series of 56 25-cent pieces (quarters) issued by the United States Mint, which began in 2010 and lasted until 2021. The obverse (front) of all the coins depicts George Washington in a modified version of the portrait used for the original 1932 Washington quarter. There were five new reverse (back) designs each year, each commemorating a national natural or historic site such as national parks, national historic site, or national forests – one from each state, the federal district, and each territory. The program was authorized by the America's Beautiful National Parks Quarter Dollar Coin Act of 2008 (Pub. L. 110–456 .
The Capped Bust coinage of the United States consisted of a half dime, dime, quarter and half dollar.
The American Palladium Eagle is the official palladium bullion coin of the United States. Each coin has a face value of $25 and is composed of 99.95% fine palladium, with 1 troy ounce actual palladium weight.
The American Liberty 225th Anniversary gold coin is a one-ounce gold coin minted to commemorate the 225th anniversary of the U.S. Mint. It was released on April 6, 2017. A companion series of one-ounce silver medals bearing the same designs was released on October 6 later that year.
American Innovation dollars are dollar coins of a series minted by the United States Mint beginning in 2018 and scheduled to run through 2032. It is planned for each member of the series to showcase an innovation, innovator or group of innovators from a particular state or territory, while the obverse features the Statue of Liberty.
The First in Flight Centennial commemorative coins are a series of commemorative coins issued by the United States Mint in 2003. The coins, issued in half dollar, dollar, and eagle ($10) denominations, commemorate the 100th anniversary of the first controlled flight of a powered heavier-than-air aircraft. The coins were authorized by Public Law 105-124.
The American Liberty high relief gold coin is a one-ounce gold bullion coin issued by the United States Mint since 2015. This coin was the first 100 dollar gold coin to be issued by the US Mint.