In 2012, Congress commissioned a special set of coins to commemorate the 75th anniversary of the Baseball Hall of Fame. The coins will come in denominations of $5, $1 and half-dollar. But what's unique about them is their shape—this set will be the first run of curved coins the U.S. Mint has ever made.

Don’t expect to find them in regular circulation though. An uncirculated $5 gold coin will cost $419.75, a silver coin will cost $47.95, and the half-dollar coin will cost $18.95.* ("Proof" coins, which "receive the highest quality strike," cost a few dollars more.) A small portion of the proceeds will be sent to the National Baseball Hall of Fame. The museum, located in Cooperstown, New York, is gearing up for its big anniversary celebration this August.

The process of making a curved coin was highly technical. The Mint described the research and development that went into creating the coin as “unprecedented.”

From Wired:

With their billiards-inspired design complete, they took the unprecedented step of CNC milling test dies themselves. “We’d never done that before,” Antonucci says. Whereas it usually takes months to get first dies for standard commemorative coins, here the team had prototypes just weeks into the project. The test runs went surprisingly well. Initially, the plan was to make only the gold and silver coins domed. But at some point, an order came down to make the clad, half-dollar coins (those that, like nickels, dimes, and quarters, have a copper core plated with nickel alloy) were to be curved as well. This was another challenge–Antonucci called the clad coin his “nemesis”–as introducing additional metals increased the risk of warping and die defects. But his team eventually got the kinks ironed out, tweaking the shape of the dome and the severity of the relief to make it all work. This coin is the first clad domed coin produced anywhere in the world.

The reverse side of the coin, depicting a baseball glove, was designed by baseball enthusiast Cassie McFarland, an artist in San Francisco. Though this was the first curved coin designed in the United States, other countries, including Australia and France have done it before, and were consulted by the U.S. Mint during the development of this coin.

There was another commemorative coin issued by the U.S. Mint this year, commemorating the fiftieth anniversary of the Civil Rights Act of 1964. That one will cost you $54.95, if you choose the fancier version. It's flat, just like any coin, but it does honor "one of the cornerstones of the civil rights movement," which is pretty special all on its own.

*This sentence originally reported only the surcharges that will go to the National Baseball Hall of Fame. It's been updated to list the total cost of the uncirculated version of the coins.