I have found a 1974 quarter that is completely brown. I have seen similar images of this coin circulating around the internet. I have thoroughly cleaned it and have tried scratching it off. I have read a forum (see link) but it seems it is old and came to no conclusions. I'm ruling out the possibility of it being stained by earth because it appears to only happen to the 1974 quarter. Is this a completely copper coin? Is it a mistake? Is it rare? https://www.cointalk.com/threads/brown-1974-quarter.17271/
I am by no means an expert, but I have dug many quarters metal detecting that look similar. After much washing they still keep that color. Not sure if that's the case with yours.
bhh is correct. Your coin suffered environmental damage. Being buried is one of the major causes of this discoloration. There are a couple posts every week asking about discolored coins just like this. Sorry, but it's not rare and only worth face value
