This rare error occurs when the coin's obverse (front) side is struck twice, resulting in a noticeable doubling of the date and the phrase "In God We Trust."
The rarity and historical significance have driven the value of these quarters to exceed $30 million at auctions, particularly when in pristine condition.
Proof coins are specially made for collectors using a high-quality minting process that results in a mirror-like finish.
The 1976 Bicentennial Quarter proofs, particularly those struck at the San Francisco Mint and bearing the "S" mintmark, are highly collectible.
Some of these flawless proofs have fetched prices exceeding $30 million in private sales and auctions.
While most Bicentennial Quarters were struck in copper-nickel clad, a limited number were minted in a silver-clad composition.
These quarters, containing 40% silver, were primarily produced for collector sets but a few made their way into circulation.