Three sisters from the US who inherited a dime coin kept it in a bank vault for more than 40 years, and while they know it had some value, they didn’t know just how much until a few years ago.

The rare coin, struck by the US Mint in San Francisco in 1975, could be worth more than $US500,000 ($748,000), according to Ian Russell, president of GreatCollections, the auction house selling the coin.

What makes the coin depicting President Franklin D. Roosevelt so valuable is that it is just one of two coins missing the “S” mint mark for San Francisco.

The other dime sold for  $US682,000 (over $1 million) at a 2019 auction and then again months later to a private collector.

While avid coin collectors have known about the existence of these two extraordinarily rare coins, their whereabouts had remained a mystery since the late 1970s.

“They were hidden for decades,” Russell said.

“Most major collectors and dealers have never seen one.”

The three sisters from Ohio, who want to remain anonymous,  inherited one of the two dimes after the recent death of their of their brother, Russell said.

They told Russell that their brother and mother bought the first error coin discovered in 1978 for $27,225, which would amount to roughly $135,000 today.

Their parents, who ran a dairy farm, saw the coin as a financial safety net, and it was only until last year that one of the sisters saw the coin first-hand.

Russell also said that their brother had reached out to him about seven years ago and told him about the coin, but he too kept it a secret.

When Russell told one of the sisters about the potential value of the coin, she told him: “is that really possible?”.

The coin, known as the “1975 ‘no S’ proof dime,” will be displayed at a coin show beginning on Wednesday in Tampa, Florida, and before the auction closes late next month, Russell said.

The current highest bidder has offered $US250,000 ($374,000).

Images: Great Collections/ Professional Coin Grading Services

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