I have read both, that it is, and that it isn't. It isn't as hard as glass, so it may be difficult to work. That was why I was wondering about heat treating it. It is very good looking stuff, and the place to gather it is only about an hour and a half from my house. My inlaws have a few boulders (150 plus pound rocks) of it in their rock garden. Next time i'm there I will sneak a chunk and see how it breaks.