And there's a reason for their scarcity: Even back in the first years of the Republic, people hoarded dollar coins rather than spend them.
The story goes that on Oct. 15, 1794, chief coiner Henry Voigt coined the silver dollars and delivered all the acceptable ones, 1,758 of them, to David Rittenhouse, director of the US Mint, according to the Smithsonian Museum of American History. He handed them out as gifts to dignitaries. In all likelihood, fewer Americans saw those silver dollars than today's Sacagawea and presidential $1 coins, which occasionally pop up in circulation.
Back then, Americans often relied on foreign coins that circulated around the young nation for dollar equivalents. Only 140 of the 1794 so-called Flowing Hair silver dollars are thought to exist. (The coins depict a woman with long flowing hair).
"I don't know what it is in the American psyche" that causes the hoarding of dollar coins, says Jeff Ambio, numismatic consultant for Bowers and Merena, the rare-coin auction house that handled the Boston auction this past weekend.
Maybe it goes back to early American history, he speculates. "In the earliest years of this country and extending back into colonial times, this society was a cash-starved society. There was very little circulating coinage. What little there was, the vast majority wasn't made over here."
The $1 coin that sold in Boston to an anonymous bidder was considered the fourth best specimen of the six mint 1794 silver dollars known to exist. The best specimen, called the Neil/Carter/Contursi 1794 Flowing Hair silver dollar, sold for nearly $7.9 million in May, setting a new record price for a coin.
[Editor's note: This story was slightly changed and updated with new information from Mr. Ambio.]