Certified Error Coins
With billions of coins produced each year by the United States Mint, it is inevitable that a few might experience inadvertent flaws or abnormalities within the minting process. Such error coins typically occur with extreme rarity and are avidly pursued by some coin collectors.
The rarity of the different types of errors can vary across the denominations and years of issue. Generally, errors with larger diameter coins occur with less frequency compared to smaller coins. Errors on circulating coins are more likely to escape detection than numismatic coins. Since early 2002, modifications to the production process have greatly reduced the occurrence of certain types of errors.
Due to their nature, nearly every error coin will have some unique aspects, although many of these will fall into one of several broad categories established by collectors.
Some of the more frequently encountered errors include clipped planchets where a portion of the metal is missing, off center strikes where the coins were struck incorrectly centered, and broadstrikes which were struck outside the retaining collar. At the start of the Presidential Dollar Program, missing edge lettering errors were common until the production process was modified.
Less frequently encountered errors include coins which have been struck multiple times, coins struck on the wrong planchet or wrong metal, and mule errors where coins are struck with obverse and reverse dies intended for different coins.
As with many other segments of collecting, it is often useful to certify error coins. A third party company with authenticate the piece, describe the error, and assign a numerical grade. This site includes additional basic information on error coins and a selection of certified errors available for sale.