The dime, minted in San Francisco in 1975, is an extraordinarily rare coin that could potentially fetch more than $500,000. Ian Russell, the president of GreatCollections, a currency-specializing company handling an online auction set to end in October, confirmed its immense worth.

The exceptional value of this particular dime, featuring President Franklin D. Roosevelt, lies in the absence of the "S" mint mark denoting San Francisco. It is one of only two coins known to exist without this mark. The existence of these rare dimes has been recognized by serious coin collectors for some time, but their whereabouts remained a mystery since the late 1970s.

"They were hidden for decades," stated Ian Russell, emphasizing the rarity and elusiveness of these coins. According to him, most prominent collectors and dealers have never even encountered one of these extraordinary dimes before.

In 1975, the U.S. Mint in San Francisco produced over 2.8 million special uncirculated "proof" sets, each containing six coins and sold for $7. A few years later, collectors discovered that two dimes from these sets were missing the mint mark. The sisters from Ohio recently inherited one of these two dimes following the death of their brother. To preserve their anonymity, they wish to remain undisclosed given their sudden windfall, according to Russell.

The sisters shared with Russell that their brother and mother purchased the first discovered error coin for $18,200 in 1978, amounting to roughly $90,000 in today's currency. Their parents, who ran a dairy farm, saw the dime as a financial safety net. One of the sisters mentioned that her brother often spoke about the rarity of the coin, although she only laid eyes on it last year.

Russell, based in Irvine, California, revealed that their brother reached out to him approximately seven years ago and divulged the existence of the coin. Russell, respecting the secrecy, kept the revelation under wraps until a few years ago when he informed one of the sisters about the coin's potentially substantial value. The sister reacted with disbelief, questioning the possibility.

The "1975 'no S' proof dime," as it is now known, will be exhibited at a coin show commencing in Tampa, Florida, on Wednesday. Following the conclusion of the auction in late October, Russell expects this rare dime to change hands for a significant sum. He also noted that while there may be a chance of finding more examples of this rare dime, they would only be discovered within the 1975 "proof" sets, ruling out the possibility of chance encounters in pocket change.

This remarkable discovery not only showcases the incredible value hidden in everyday items but also serves as a reminder to diligently inspect inherited collections or possessions for hidden treasures.