In numismatics, a mule is a coin or medal minted with obverse 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.
Several prominent mule errors have been discovered in recent times. One of the most famous is the Sacagawea Dollar/ 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. 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. One of the few that escaped detection was sold on eBay for $41,295.
