In numismatics

Numismatics

Numismatics is the study or collection of currency, including coins, tokens, paper money, and related objects. While numismatists are often characterized as students or collectors of coins, the discipline also includes the broader study of money and other payment media used to resolve debts and the...

, a mule is a coin or medal minted with obverse and reverse

Obverse and reverse

Obverse and its opposite, reverse, refer to the two flat faces of coins and some other two-sided objects, including paper money, flags , seals, medals, drawings, old master prints and other works of art, and printed fabrics. In this usage, obverse means the front face of the object and reverse...

 designs not normally seen on the same piece. These can be intentional or produced by error. This type of error is highly sought after, and examples can fetch steep prices from collectors.

The earliest mules are found among ancient Greek and Roman coins. Opinion is divided between those who think that they are accidental, the result of an incorrect combination of a new die with one that had officially been withdrawn from use, or the work of coiners working with dies stolen from an official mint, perhaps at a time when one of them should have been destroyed.

The name derives from the mule

Mule

A mule is the offspring of a male donkey and a female horse. Horses and donkeys are different species, with different numbers of chromosomes. Of the two F1 hybrids between these two species, a mule is easier to obtain than a hinny...

, the hybrid offspring of a horse and a donkey, due to such a coin having two sides intended for different coins, much as a mule has parents of two different species.

Prominent modern mule errors

Several prominent mule errors have been discovered in recent times. One of the most famous is the Sacagawea Dollar

Sacagawea dollar

The Sacagawea dollar is a United States dollar coin that has been minted every year since 2000. These coins have a copper core clad by manganese brass, giving them a distinctive golden color. The coin features an obverse by Glenna Goodacre. The reverse design has varied, from 2000 to 2008...

/Washington State Quarter mule featuring the obverse of a Statehood quarter and the reverse of a Sacagawea dollar. This coin was struck on a Sacagawea dollar planchet

Planchet

A planchet is a round metal disk that is ready to be struck as a coin. An older word for planchet is flan. They are also referred to as blanks.-History:The preparation of the flan or planchet has varied over the years...

. Common belief was that this coin was intentionally struck by a mint employee, however the mint confirmed in July 2000 that the coin was a legitimate error, created by the accidental replacement of a cracked Sacagawea obverse die with a Washington obverse die. Several thousand of the coins were reported to have been minted before the error was discovered, and mint employees recovered and destroyed most of them. As of July 11, 2011, eleven are publicly known to exist and have been certified. One of the few that escaped detection was sold on eBay

EBay

eBay Inc. is an American internet consumer-to-consumer corporation that manages eBay.com, an online auction and shopping website in which people and businesses buy and sell a broad variety of goods and services worldwide...

 for $41,295.

In February 2009, Coin World

Coin World

Coin World is an American weekly numismatic magazine. It is the world’s #1 publication for coin collectors and the weekly newspaper of the entire numismatic field...

reported that some 2007 Abigail Adams

Abigail Adams

Abigail Adams was the wife of John Adams, who was the second President of the United States, and the mother of John Quincy Adams, the sixth...

 medals, from the U.S. Mint, were struck using the reverse from the 2008 Louisa Adams

Louisa Adams

Louisa Catherine Johnson Adams, born Louisa Catherine Johnson , wife of John Quincy Adams, was First Lady of the United States from 1825 to 1829.-Early life:...

 medal, apparently by mistake. These pieces were contained within the 2007 First Spouse medal set. The U.S. Mint has not released an estimate of how many mules were made. Ebay prices in March 2009 were reported as high as $925.99.

In 1967, a New Zealand

New Zealand

New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

 2 cent coin was issued, featuring the obverse of the Bahamian 5 cent coin, see Coins of the New Zealand dollar

Coins of the New Zealand dollar

This article concerns the coins of the New Zealand dollar.- Pre-dollar :Prior to 10 July 1967, the New Zealand pound, using the £sd system, was the currency of New Zealand. Coins of the pound tend to follow the size, weight, and composition of their British counterparts...

.

In June 2009 a rare dateless British 20 pence mule was reported to be in circulation, resulting from the accidental combination of old and new dies in production following a 2008 redesign of UK coinage, with an estimated 50,000 to 200,000 mules released before the error was noticed.

The Winter Olympic coins

Winter Olympic coins

Although the first Olympic coin can be traced back to 480 BC, the modern Olympics did not see its first commemoratives until 1951. The original concept of Olympic coins was that the Greeks believed that coins brought the general public closer to the Olympic games. The premise was that those who...

 produced in the Royal Canadian Mint Olympic coins

Royal Canadian Mint Olympic coins

-1976 Montreal Summer Games:Most numismatists agree that the first true numismatic collection was the Olympic Five and Ten Dollar coins for the 1976 Montreal Olympics. Starting in February 1973, the Royal Canadian Mint engaged in a very ambitious program...

 program for the 2010 Winter Olympics

2010 Winter Olympics

The 2010 Winter Olympics, officially the XXI Olympic Winter Games or the 21st Winter Olympics, were a major international multi-sport event held from February 12–28, 2010, in Vancouver, British Columbia, Canada, with some events held in the suburbs of Richmond, West Vancouver and the University...

 in Vancouver

Vancouver

Vancouver is a coastal seaport city on the mainland of British Columbia, Canada. It is the hub of Greater Vancouver, which, with over 2.3 million residents, is the third most populous metropolitan area in the country,...

featured several mules which entered circulation.