A rare US dime, an unstamped dime, has been auctioned for $506250, nearly 30 times the price it sold for 46 years ago.

GreatCollections, which auctioned the 1975 Ten without an S, said the coin was purchased by an Ohio collector and his mother for $18200 in 1978 and remained in the family for nearly 50 years.

A rare US dime without a stamp has been auctioned for $506,250, almost 30 times the price it sold for 46 years ago.

GreatCollections, which auctioned the 1975 Ten without an S, said the coin was bought by an Ohio collector and his mother for $18,200 in 1978 and stayed in the family for nearly 50 years.

The collector's family decided to put the coin up for auction, and it was graded Proof-67 by the Professional Coin Grading Service before it sold for $506,250, according to upi.com.

“We had interest in this modern rarity from all over the world – serious collectors from Germany, Japan and the United Kingdom, as well as collectors from the United States – with over 400 unique bidders attending the auction,” said GreatCollections president Ian Russell.

The dime is unique because it does not have the "S" mark, which shows that it was made in San Francisco. It is one of only two known examples that still exist.

“This is the Grail of modern coins, one missing from the institutional collections of the Smithsonians, ANS and ANA. After bidding, it was eventually won by an early customer of ours who appreciates rarities that rarely appear on the market. His intention is for the family to own it for the next 46 years, just like the family of the seller who consigned it to GreatCollections,” said Russell.