That's killer, Mike. I'd call it a backed knife. A hand knife. Real nice, super tool. Looks like it may be ground on the flat sides.
That kind of patination in FL is most often quite old boom. Looks also like the maker was trying to thin, possibly flute the base......and right after that realized he was gonna wind up with a tool. That really has a paleo look to it, like Suwannee, but what do I know?! muhaha.