The Mint Act of 1792 established the Mint of the United States. The Mint, in its first decades, only coined gold and silver in response to deposits of that metal by citizens, returning the bullion to the depositor in the form of coins. Either gold or silver could be presented for conversion into currency, as both metals were a legal tender, a dollar was equal to both a legally defined weight of silver, and another legally defined quantity of gold. Having a currency defined in terms of two different metals is called bimetallism. Such a system may experience instability as the price of gold and silver on the world market changes, and this took place in the first decades after 1792, as the relative values of gold and silver in Europe changed. At that time, gold or silver U.S. coins were rarely seen in the nation, as they were heavily exported because of such shifts—most pieces in circulation were foreign in origin.