I found some small pebbles of very fine-grained basalt when I lived in oregon...it knapped really well and was almost like slightly tougher Dacite. It worked great. If you can find some of that, it would work. But then again, if you want to try to make a point out of that stuff, be my guest. I'll bet it would sound like a pipe organ if you actually made a point out of it, tied it to an arrow and then shot it....