ELECTRUM is a naturally occurring alloy of gold and silver, first used for coinage in ancient Lydia in the 7th century BCE, and its color ranges from rich gold to a pale, greenish hue depending on its composition. The word comes from the Greek elktron, which referred to both electrum and amber. Because amber produces static electricity when rubbed, this same root eventually gave rise to words like electric and electron, linking electrum etymologically to light and charge.