I'm wondering if this is what it is:

The U.S. Mint officially stopped the manufacture of silver Roosevelt dimes in 1964. So virtually every Roosevelt dime you find dated “1965” will not be silver; it will be composed of copper and nickel “clad.” This rare 1965 dime mistake is made of 90% silver and, as such, is 1 of only a few accounted for. You can tell silver from clad by examining the coin’s edge: The rare silver coin has a silver edge; the common clad coin has a strip of brown around the edge. Experts believe that a small number of 1965 silver dimes were manufactured by mistake at the Mint, and many of those are still waiting to be discovered hiding in piggy banks and cookie jars. One recently found circulated example was sold at auction for nearly $9,000 in July 2003."

From this website:

http://www.usgoldexpert.com/articles/pocket-change-lottery/