Strange wear on US dollar 1978

I just got this from the bank.You can see the copper under the chr nickel.Is it just wear, like some ascid. Or a clad issuse?


any thoughts? thank you yours daryl

Hi,

  It does look odd. Maybe the cu-ni coin acid treated or something. What is the weight?

Perhaps it has spent some years underground and was cleaned after recovery?

The weight is good
 But i think it was in the ground for some time,thinking about it.They use salt here for the ice. And the edge show some green on it. Thank you for your help
             yours daryl