LAS VEGAS >> The coin trading world has a new gold standard, after the only known 1822 half eagle $5 piece in private hands sold at auction in Las Vegas for $8.4 million, experts said today.

Douglas Mudd, curator and director of the Edward C. Rochette Money Museum in Colorado Springs, Colorado, confirmed the coin is one of three of its kind in existence and the auction price Thursday was the highest for a U.S. gold coin struck by the U.S. Mint.

The most expensive U.S. coin ever sold, at $10 million, is a 1794 U.S. “Flowing Hair” silver dollar said to be among the first-ever minted in the fledgling United States.

The 1822 half eagle $5 coin came from the D. Brent Pogue Collection and the buyer wanted to remain anonymous, said Jarrod Holland, spokesman for Stack’s Bowers Galleries, host of the public auction in Las Vegas. He provided a video of the coin.

Brett Charville, president of Professional Coin Grading Service in Santa Ana, California, said he graded the coin as AU50, or almost uncirculated.

Two other 1822 half eagle $5 gold pieces are permanently held by the National Numismatic Collection at the Smithsonian Institution, Holland said.

The half eagle was acquired by a collector in 1899, sold in 1945 and acquired by Pogue in 1982.

The price surpassed the $7.6 million paid in 2002 for a 1933 double eagle, according to the U.S. Mint.