Editor's Note: This Cent/Dime Mule sold for $138,000 in the Heritage Galleries Aucition at the Central States coin show. Here is the description from the auction listing:

1999 1C Lincoln Cent Obverse Die Muled With a Roosevelt Dime Reverse on a Lincoln Cent Planchet MS66 Red PCGS. This incredible error somehow escaped the scrutiny of Mint employees. We are uncertain how a Lincoln cent obverse die was paired with a Roosevelt dime reverse, but this coin proves that it happened. No others are known to exist: it is believed that the present muling of a cent obverse with a dime reverse is unique. Cross-denomination errors are all but unheard-of from the U.S. mints. The only other examples that come to mind are the Sacagawea dollar/Washington quarter mules, of which about a dozen are known. Incredibly, this type of error occurred only recently, during the entire history of U.S. coinage that spans more than 200 years.

The obverse is sharply struck on the figure of Lincoln and the date, although the opposing dime die, being slightly smaller than the cent planchet, caused minor peripheral weakness on the obverse. In other words, nothing was behind the periphery of the cent die to force the expanding metal into the recesses. Naturally, the slightly smaller reverse dime die caused that side to be boldly struck. Shortly after this phenomenon dropped from the (mismatched) dies, it was discovered in a jewelry store in Michigan before entering circulation. It has since been carefully handled, and has developed no spots or other distractions. The coin remains a solid Premium Gem MS66, with full mint Red.

For the error specialist, this would be the centerpiece of an advanced collection. All error collectors will long remember the present coin and hope that someday it will again be publicly offered. This piece was widely publicized in Coin World and Numismatic News soon after its discovery. Since then, it has passed to two or three owners. This prize represents a unique opportunity. It is undoubtedly one of the most important highlights of this or any numismatic auction.