A copper dime is a coin that lacks its outermost layer of metal, revealing the copper layer underneath. All dimes minted since 1965 are composed of a copper core with a copper-nickel blend applied over the surface to give them a silvery sheen.
This kind of error is called a "clad coin" by coin collectors. It is caused by gas or dirt getting between the metal layers during the lamination process. This prevents the copper-nickel laminate from adhering to the coin. When the coin is cut free from the blank on which it is stamped, the laminate falls off. Clad dimes bearing President Franklin D. Roosevelt's image are worth $6.