That's some pretty tough looking stuff, looks like porphyritic rhyolite (rhyolite containing phenocrysts of quartz, feldspar, pyrite and such), some of which is pretty hard to knap, and some of which isquite knappable. From what I can find, the prehistoric people in New England used Kineo Rhyolite extensively, so it may be decent stuff. Tell you what, if you're interested, I'll trade you a couple good chunks of obsidian or something for a couple good chunks of that stuff-that way I can beat on some of it and can give you some better advice on working it.