The preform is some heat treated rock or what we call bull rock from the colorado river in wharton county.As for the other ones that is a good question.I heated these from my scrap pile.I know that one rock was some stuff that was given to me by one of your members.It came from i beleive central texas.I don't have good quality stone here so i have to really struggle with river rocks.Most are round,some are too glassy,some will work raw,but heat will make them work better.