What is the name of the natural alloy of gold and silver?

The natural alloy of gold and silver is called electrum.

Electrum occurs naturally, although it can also be manufactured by deliberately mixing gold and silver. Its color varies from pale yellow to bright yellow according to the proportions of the two metals; natural samples may also contain traces of copper, platinum or other elements.

The alloy has a particularly important place in ancient history. Egyptians used electrum as a decorative coating on pyramidions and obelisks, while the Lydians and Greeks used it for some of the earliest known coins, beginning in the seventh century BCE. Electrum was harder than pure gold and more durable for coinage, but its variable composition made its exact value difficult to judge.

Electrum is not the same as modern white gold. White gold is a deliberately made gold alloy with metals such as nickel, palladium or platinum. “Green gold” is sometimes used for electrum, but the natural alloy is usually better described as pale or silver-yellow.