I doubt if any of you would call this an error coin, but it is unusal to me. All my other similar coins are bright and shiny. What causes a coin to discolor from clad silver to a dark non-metalic finish?
Clad coins tarnish heavily in the ground. Your coin could have been dropped and spent several years in or on the ground before being found (possibly by a metal detectorist). Many of the clad coins that I have found with my metal detector look like your quarter.
