Quarters minted in 1964 in the United States contain 90% silver and 10% copper. The total silver weight within a single coin of this type is approximately 0.18084 troy ounces, or roughly 5.625 grams. This composition distinguishes it from subsequent coinage, which transitioned to a clad metal construction.
The significance of the silver content stems from its intrinsic value and historical context. Prior to 1965, circulating U.S. coinage was largely composed of silver. As the price of silver rose in the early 1960s, the intrinsic metal value of the coins began to approach, and at times exceed, their face value. This spurred a transition to cheaper metals to prevent widespread melting of existing coins for their silver content.