A Mexican 1538 eight reales silver coin is to lead a sale at Daniel Frank Sedwick on November 6 in Orlando with a $500,000-1m estimate.
The lot is the first dollar-sized coin ever minted on the American continent and is one of three discovered in a shipwreck in 1990.
One, in lesser condition, sold for $373,750 at Heritage Auctions in 2006.
Daniel Sedwick, founder and president of the company, commented: "We cannot overstress the importance of this auction, both for the history of Mexico and the larger field of North American numismatics".
"These coins are the absolute root of the concept of the American dollar."
The coins were struck under the reign of Carlos and Joanna of Spain, just over 10 years after Hernan Cortes' conquest of Mexico ended with the Destruction of Tenochtitlan.
Sedwick went on: "Only three people or institutions, at most, can own a specimen of this highly important coin and opportunities like this are as rare as the coins themselves."
Vice President Agustin Garcia-Barneche, commented: "We already have interested parties, which mean this coin could break the record for the highest price ever paid for a 'dollar' that was not struck at a US mint.
"There will be worldwide interest, not just for the coin's historical importance but also because collectors are confident about its extreme rarity."
We have a fascinating selection of coins and banknotes available.
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