Electrum occurs naturally, and has been known since ancient times. The ancient Greeks called it 'gold' or 'white gold', as opposed to 'refined gold'. Its colour ranges from pale to bright yellow, depending on the proportions of gold and silver.
Electrum is believed to have been used in coins around 600 BC, in Lydia (western Anatolia). It was much better for coinage than gold, mainly because it was harder and more durable, but also because techniques for refining gold were not widespread at the time.
It's sometimes found with traces of platinum, copper, and other metals. It has also been produced artificially, and is often known as 'green gold'.
© Haydn Thompson 2017