The original $50 coins were almost lost when, after they were struck in 1877, Chief Coiner Archibald Snowden suddenly left the U.S. Mint, and the coins disappeared, too. Eventually the solid gold coins were returned to the Mint. Experience first hand the dazzling design and massive size of the largest gold coin ever struck. Reserve your proof today! It's also one of the rarest coins in the history of the United States as it was only struck twice in solid gold. Both now reside in the Smithsonian, and they are literally priceless. Until now, just viewing this magnificent design was a rare opportunity. But today you can reserve your very own 1877 Half Union Proof, measuring almost 51 mm in diameter.