Quarters and dimes minted by the U.S. Mint contained silver up until 1964, when the precious metal was removed in favor of a more economical composition: copper and nickel. Washington quarters and Roosevelt dimes minted through 1964 contained 90 percent silver and 10 percent copper.
The rising value of silver contributed to the U.S. Mint changing the compositions of the coins to a more economical approach, copper-and-nickel clad, starting with the 1965 issue. The seldom-used half-dollar retained some silver content, 40 percent, up until 1970, when it was removed altogether. Outside of non-circulated silver proofs and collector-issued coins, the mint has not released another silver coin since the 1970 half dollar.