Welcome from east/middle Tennessee! river patina and wear like that is great. i have a few spots that turn out a similar type of look. can't tell anything for certain on chert with the pics, could be fort payne. with that much patina and no fresh breaks it is hard to tell. does the bottom of it appear to have been broken? if so, it might be a broken tip of a point like terry mentioned. it almost looks like one of those bottom corners is worked though. if so, would make it a pretty large triangle. either from reworking a broken tip of a larger artifact or purpose made as is. great find and thanks for sharing.