I think you can forget the idea of it being a tool, primitive tools were pretty much confined to cutting, cooking, sewing, and beating . Knowledge of primitive tools is well established, simply because there weren't that many. I seriously doubt there's going to be a discovery of a heretofore unknown tool. If the piece is as old as you think, then it must be an ornament. It's not a weapon, not useful for procuring food or cooking it, not useful for making clothes, not a potato digger. If you want to narrow things down, you can start by eliminating everything invented after the foundation for the first pyramid was laid. Failing that, call it a mistake someone made and threw away.