Those are sweet finds. That's no preform. It's a completed piece. I often find pieces that thick down on my family's farm. The farm has lots of red clay and is so mineral rich I could never medal detect down there. In parts of the county with less mineral or metallic content in the soil, I've noticed my finds are flaked much thinner, with smaller reduction flakes. I hypothesize stones with higher iron, or other hard mineral content were harder to work. If not that, they were made in a manner that allowed multiple reworks after impact. That is my hypothesis, based on my observation. You guys may draw the conclusion that I'm full of bull snot. Lol! Nice finds any way!!