The final year that the United States Mint produced circulating quarters composed of 90% silver was 1964. Prior to this date, quarters, dimes, and half dollars were minted with this high silver content, giving them intrinsic value beyond their face value. Coins from 1964 and earlier are often sought after by collectors and investors due to their precious metal content.
The shift away from silver coinage occurred due to rising silver prices. As the value of silver exceeded the face value of the coins, there was a risk of them being melted down for their metal content. Removing silver from circulating coinage was necessary to stabilize the monetary system and prevent a potential coin shortage. This transition marked a significant change in the composition and value of American currency.