What years did the US mint silver quarters?

Circulating quarters were made of 90% silver and 10% copper from 1796, the first year of issue, until 1964. Increases in the price of silver forced the Mint to switch to the current copper-nickel clad composition in 1965.

Special 40%-silver quarters were made for sale to collectors during the Bicentennial, and starting in 1992 90% silver quarters have been struck for sale in "Prestige" proof sets. None of these were ever intended for circulation, though.