Norfolk southern uses trap rock on their rail in the MS area from North Carolina and VA. It is basically a type of Basalt. I am an ameture when it comes to knapping but a fellow from IL that I had a chance to spend some time with last year told me a neat rule to follow while you are a newbe, heat it if its white dont heat if its black. If it is basalt then it is silica poor and besides not benefiting from it, it may explode.
