Here is a favorite point a found some years back. I am going to call the material unknown, maybe Glacial till. It measures almost 2 3/4 inches from Central Illinois.
Thanks Larson. As far as its use, that is a good question and I am not sure of the answer. I think it was an atlatl dart point. I am basing this on its thickness, although the hafting area seems a bit wide for a dart. It is cracker thin....about 6 mm. I would be interested what others think.