Electrum, although also been produced artificially, is an alloy of gold and silver which occurs naturally and is commonly known as ‘white gold.’ It also contains very small or trace amounts of metals such as copper.
“The ancient Greeks called it ‘gold’ or ‘white gold’, as opposed to ‘refined gold’. Its color ranges from pale to bright yellow, depending on the proportions of gold and silver. The gold content of naturally occurring electrum in modern Western Anatolia ranges from 70% to 90%, in contrast to the 45–55% of electrum used in ancient Lydian coinage of the same geographical area. This suggests that one reason for the invention of coinage in that area was to increase the profits from seignorage by issuing currency with a lower gold content than the commonly circulating metal” (Wikipedia).
“Electrum was used as early as the third millennium BC in Old Kingdom Egypt, sometimes as an exterior coating to the pyramidions atop ancient Egyptian pyramids and obelisks.” In addition, it “was also used in the making of ancient drinking vessels and coins” (Wikipedia).