A US 1792 silver disme has starred in the Central States Numismatic Society (CSNS) sale in Chicago.
The AU50-graded coin made $998,750 on May 1 at Heritage Auctions.
The origins of the coin are mysterious. Rumour has it, the silver used in its manufacture was donated by George Washington.
Supposedly he gave the US Mint some of his own tableware to melt down, although this has never been conclusively proven.
Heritage comments: "In contrast to the 1792 half disme, there is little in the historical record that directly addresses the disme of the same year.
"Only three examples are known to collectors today, with two specimens struck on a normal flan and another on a thick planchet, with the date effaced.
"The present coin is by far the finest-known example, having graced the fabulous collections of Dr. J. Hewitt Judd and Donald G. Partrick."
Other lots in the sale included a 1776 Continental $1 (in pewter), which realised $235,000.
No documents authorising the production of this issue have ever come to light, but it is thought to have been introduced due to a shortage of paper dollars.
It was struck in three different materials; pewter, silver and brass.
Only three silver examples are known to exist, with one selling for a record $1.4m at Heritage in 2014.
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