And the 'blade' end-- the 'bit'? Grooves can be made by many things, erosion by sand, other rocks, dirt, water, etc. Rocks move and chip. Unless there's a blade to that puppy... Now, depending on where you are (I don't remember if you said)- if you're near water, it might have been an anchor? or maybe way heavy-duty net weight? I don't know. But I'm not convinced. Now, not all tools are all pretty and refined, but most of them are. If they're ground hard-stone, they're more than likely carefully and beautifully made. Strong, efficient, symmetrical and all that. Generally, you don't really need a half dozen pictures to convince someone that something is a tool. Take a look at the images above. Do you need a different angle to be sure they're really real? It isn't just one feature that tells the tail. It's the bit, the ground hasping area, the (generally) smooth texture, the symmetry, the beauty of the chosen stone (tho not all are pretty- mine are plane- and river-worn).
Someone might come one board and tell me I'm wrong and there's a tool that looks like that- or weapon. Then I'll be the one learning. In the mean time, I stand firm. I'm sorry.