After a massive importation of gold bullion during the California Gold Rush, silver could be traded for increasing amounts of gold, so U.S. silver coins were exported and melted for their metal. This, and the reduction of postage rates to three cents, prompted Congress to authorize a 3-cent piece in 1851 made of 75% silver. The 3-cent silver coin was the first American coin to contain metal valued significantly less than its face value and the first silver coin to be a legal tender for only a limited amount. Weighing only 0.80 grams, it is also the lightest U.S. coin ever minted. The original obverse design featured a star bearing the Union shield, while the reverse depicted an ornamental C (for cents) surrounding the Roman numeral III. The composition was later changed to 90% silver in 1854, and the coins were subsequently hoarded during the Civil War. A nickel 3-cent piece was introduced in 1865 that co-circulated with the silver version until the latter was discontinued in 1873. By today’s standards, the highly unusual silver and nickel three-cent coins are highly popular amongst collectors and numismatic investors alike.