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 off 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. While it closely resembles silver dollars that were later minted in Philadelphia, it gets its name because it is missing stars. Jacob Lipson of Heritage Auctions said earlier that starless coins are considered by collectors and institutions as “one-of-a-kind prototypes for the silver examples that would follow,.” Known as a …