it's worth 25 cents. the "copper" you are thinking is from environmental damage. Probably stuck in the ground for some time. coins are made of metal. Metals can tone and "rust" over time plus can be impacted by a variety of substances.
That one looks like it spent some time hidden away under the hydraulic lift in an auto repair shop exposed to the grease and oil and other elements. I would also say worth 25 cents. TC
@James Alexander Clad coins and even nickels contain Cupro-Nickel. It has copper mixed in.. So when exposed to the elements it gradually changes color. Here are my metal detected examples -
Your quarter is not copper but have a copper core. The outward appearance that you're seeing is environmental damage. It's worth $.25. Welcome to CT.
Everytime i see that coin. It freezes me. And trip about what i would do with that coin. I now know the answer. I'd keep it