There is a huge difference. Celts will almost always be symmetrical and entirely rounded except for the sharpened and usually well worn cutting edge. In my 12 years of collecting native American artifacts and looking through my father's 40year collection which includes roughly 100 examples, no Celt was ever shaped like that, or made from that type of material. I see no indication of tooling marks or usage, and I've never seen one made from that particular material. My guess is a well worn River rock, probably a type of limestone judging by the white color.