Electrum alloy deposit (yellow), with a paper clip for scale. Electrum is a naturally occurring alloy of gold and silver. It can also contain trace amounts of other metals, such as platinum and copper. This alloy was used to make coins in cultures such as Ancient Egypt and Greece, and the alloy was used during the first millennium BC until pure silver and gold coins were introduced. This sample is from Altai in southern Siberia, Russia. The sample measures 25 by 35 millimetres.