IMHO...it appears to have been "tagged" by an earlier CRH...with the color wearing off. I initially thought it to have been a "dug" coin that has spent some time in the ground giving up its finish to the mineralization in the dirt, but after looking a little closer...paint. thx ddf.
Guessing from the looks of the coin with the blackish and brownish debris and staining on it and the Copper showing through, I would say that the coin was in a fire. It probably was not in the fire long but just long enough to cause the Copper core to bleed through the Cladding.
perhaps this was used in one of those high school science experiments whey they electroplate things with copper. Coins and keys were popular choices when I was in school.