25Mn Because nickel was a scarce strategic metal during World War II, from 1942 to 1945 US 5 cent pieces were made of 56% copper, 35% silver and 9% manganese. This particular alloy was chosen to duplicate the electromagnetic properties of copper-nickel in vending machines. For similar reasons, today's "golden" Sacagawea and Presidential dollar coins are 7% manganese brass with a pure copper core. (not listed in J&M)