Editor's Note: This Washington quarter mint error is in the upcoming Stacks' Bowers June 2026 Showcase Rarities Night. This truly is a remarkable transitional mint error since the normal transitional quarters and dimes that were struck in silver instead of clad are dated 1965.

1965 was the year that the U.S. Mint transitioned from striking 90% silver quarters and dimes to a much less expensive clad composition. There are a few known silver quarter and dimes dated 1965 and they are prized by mint error collectors and sell anywhere from $6,000 to $12,500. This one dated 1966 on a leftover silver planchet (from 1964) may be unique and will certainly excite bidders competing for this transitional mint error.

1966 Washington Quarter
Struck on a 90% Silver Planchet
PCGS AU 53