Why is cupronickel used in coins?

Cupronickel is widely used in coins primarily because it is a durable, easily worked alloy that provides a desirable white appearance.12

Specifically, an alloy consisting of 25 percent nickel and 75 percent copper has been a standard choice for coinage since the mid-19th century, when it was first adopted by Belgium and later by the United States. Beyond its aesthetic qualities, the alloy is valued for being stronger and more resistant to oxidation than pure copper. In modern applications, such as the U.S. 10-cent and 25-cent pieces, this cupronickel composition is often used for the outer layers of the coin to provide a resilient, attractive finish over a copper core.12