Probably not worth keeping but I thought I'd ask. Mint mark is not distinct but is there ("P"). Keep it or throw it in the coin machine pile?
Whenever you are asking questions about a coin, it helps to get a picture of it. Without a picture it is very hard to help but from what your are describing it just sounds like a normal quarter with some wear so i would throw it in the coin machine pile.
Probably just damage, but it might be a grease-filled die. The folks in the Error forum can probably be more helpful.
