The front of a piece of copper that was struck by the U.S. mint in Philadelphia in 1794 and was a prototype for the fledgling nation's money.

A piece of copper that was struck by the U.S. Mint in Philadelphia in 1794 and was a prototype for the fledgling nation's money was auctioned for $840,000, considerably more than expected, an official said.

Heritage auctions spokesman Eric Bradley said the “No Stars Flowing Hair Dollar” opened at $312,000 when it was put up Friday evening but “in less than a minute, intense bidding quickly pushed the coin to its final auction price of $840,000.”

The coin, formerly owned by businessman and Texas Rangers co-chairman Bob Simpson, had been expected to sell for $350,000 to $500,000, Bradley said.