try to see how much it weighs..I wonder if it could be a nickel struck on a dime planchett (please don't think it is until others with more knowledge posts..I dont want to get your hopes up and make you think it is something that is it not.)
It's nothing more than a 1973 nickel that has spent a little time in some acid: http://hermes.csd.net/~coneca/content/OhNo0035-AcidCoins.htm