Gold is not the only metal which has been used as money: First, people bartered; they swapped goods. But it wasn't always convenient and some goods didn't last all year. The very first money was probably shells. China led the ancient world by introducing shells as a medium of exchange and unit of account in commerce. Shells are durable and easy to carry and count. Silver was used a lot to make coins, probably even before gold was used. Before the gold standard system, some countries used a silver standard. Iron, copper and nickel were also used. The five-cent US coin is called a nickel, but it contains more copper (75 per cent) than nickel (25 per cent).