I found this in a roll this weekend and was wondering if it was an actual error or PMD. I'm leaning towards PMD but figured I'd ask the experts Thanks for looking.
Why would it be copper though? As I understand it, nickels are an alloy and not plated like dimes and quarters. If it was a lamination error wouldn't it still be nickel-colored?
We call it environmental damage. That's a catch-all phrase for coins that have been altered by some unknown reaction with the metal. In many cases, the coin was rediscovered after having been in the soil. This coin was probably found by someone with a metal detector. The green color also indicates that the coin has some corrosion going on.
PS: a nickel is mostly copper as far as its alloy, and environmental damage can cause the copper ions to migrate to the surface of the coin.
If that were the case would the core become nickel enriched? More likely under certain circumstances the Ni is preferentially removed at the surface leaving it relatively Cu enriched.
