Additionally, certain mint marks can add value to 1964 silver quarters. Quarters minted in San Francisco (denoted by an "S" mint mark) or Denver (denoted by a "D" mint mark) tend to be worth slightly more than Philadelphia-minted quarters. Quarters with special varieties, such as those with doubled dies or other errors, can also command higher prices.
Therefore, the value of a 1964 silver quarter can vary depending on its condition, mint mark, and potential variations. To get an accurate assessment of the value of a specific 1964 silver quarter, it is best to consult with a professional coin dealer or an expert in numismatics.