The 1966 Washington Quarter is part of the U.S. coinage system, minted without a mint mark.
It's a special coin as it belongs to the first series of clad coins, replacing silver content.
Over 800 million were produced, making it common but collectible due to its historical value.
Circulated coins are worth face value, while uncirculated can fetch $1 to $3.
Coins with errors or in mint condition can be valued higher by collectors.
Special features like double die or unique errors increase a coin's collectible value.
Grading by professional services like PCGS or NGC can authenticate and value the coin.
The highest-graded 1966 quarters can be worth hundreds or even thousands of dollars.
Collectors often seek the 1966 SMS (Special Mint Set) quarters for their collection.
Always verify authenticity and consult a numismatic expert when valuing rare coins.