You will get very little but frustration if you continue trying to knap that kind of rock. It just isn't going to work. You could buy workable material from neolithics.com or a number of other places, but it's a lot cheaper to learn on glass and the thick glass from an old TV picture tube works well for percussion. Plain window glass is pretty thin but plate glass is good, and often a broken mirror will have reasonably thick (thicker than 1/8 inch) glass. Mirrors have the advantage of having a 'cortex' (the backing) to remove and allow you to better see where your flakes are going. There's the old standby of bottle bottoms, of course. The glass will work like obsidian. To work material more like flints and cherts, find some broken porcelain; old toilet tanks (johnstone) are the standby, but anything made of porcelain will work; a broken plate, for instance. There are different qualities of porcelain, just as there are different cherts, and some will work better than others, but any will work better than what you have pictured. Good luck!
