Hi guys I am brand new to collecting coins and found this one today. I was hoping someone could point out exactly what happened to this coin as I am not an expert and can't tell if this is a mint error or something like heat damage. Thanks in advance!
Looks like a cup-holder coin to me. This happens all the time when drinks or beverages spill onto a pile of coins and then dries. The gunk stains and corrodes the coins and also hardens between coins stacked on one another leaving an impression when they are pulled apart.
Welcome to the world of coin collecting, and specifically, CoinTalk! While you might not have received the answer you were looking of this time, but keep up the search! Good luck.