1871Two known in silver. I believe the few silvers that exist were given to either the recipient's family or, more likely, the Congressman or Senator proposing the issuance of the gold Congressional medal. The original gold medal is in the National Museum of American History at the Smithsonian, located "in a high security storage unit" (evidently never on exhibit) within the Division of Politics and Reform. This information was only recently revealed after a 2 year-long inquiry with the SI w/o response. The chocolate bronze is rather rare.silver77