Jessie Yeung , CNN Written by

This coin was worth half a dollar when it was made in 1838. It has now sold for $504,000 at auction.

which described it as "a truly legendary coin ... that will forever be revered, studied and dreamed about." The 1838-O Capped Bust Half Dollar was auctioned on Friday in Baltimore by auction house Stack's Bowers Galleries,which described it as "a truly legendary coin ... that will forever be revered, studied and dreamed about."

It isn't just old, it's extremely rare. Only 20 were ever created, and the Smithsonian Institution believes only 11 still exist. Stack's Bowers says it could be as few as nine.

The specific coin auctioned is called the Cox Specimen, which last changed hands in the 1980s, according to the auction house. It features a woman wearing a band that reads "Liberty" on one face, and the national symbol of the bald eagle on the other.

It was created at the New Orleans Mint, which opened in 1838 with the purpose of creating gold and silver coins. The coins created there are stamped with the letter "O," representative of the city's name, to distinguish it from coins made at other mints.

At the time, lots of silver coins were being imported into the United States from other countries like Mexico -- but silver coins from Latin America had an "uneven quality," said the auction house.

Converting them into silver half dollars would then turn these uneven coins into ones that were "fit for banking and commerce."

According to the Smithsonian , US coin expert Walter Breen said the coins could have been made to test the capabilities of a new large press -- or perhaps were designed to be presentation pieces.

However, the mint ended up producing very few of these half dollars. The spread of yellow fever that year closed the mint for months, and technical issues halted progress -- making the existing few 1838-O half dollar coins highly coveted by modern collectors.

One of the most enthusiastic collectors was a man named "Colonel" E.H.R. Green, who once owned six of the half dollar coins, including the Cox Specimen, according to the statement. The Cox Specimen was bought and sold by several other dealers before finding its way to the auction house.

The other eight coins are either owned by dealers or are on display -- one of the coins is currently part of the National Numismatic Collection in the Smithsonian Institution in Washington, DC.

Even with the sale price of, the coin isn't the most expensive of its type.

Another 1838-O half dollar coin sold for $763,750 in 2014. Most recently, one fetched $444,000 at a Florida auction last January.

The difference in selling price depends on market forces as well as the grade and "eye appeal" of the individual coin, Vicken Yegparian, Vice President of Numismatics at the auction house, told CNN in an e-mail. For instance, the Cox Specimen has highly reflective surfaces with sharp and distinct features.

Stack's Bowers Galleries has made headlines for astronomical sales before -- a famous silver coin dated 1794 sold for over $10 million in 2013, setting the world record for highest auction price for a rare coin.