Tey don't break too bad while making them. If each flake detaches smooth, it makes the platform for the next one. If ya slip or round off a platform then it takes more pressure and more likely to break.
I use a slightly domed hand pad with a notch about 3/16" wide and support the piece with my fingertips directly behind where I'm flaking. I broke a lot at first but don't break too many these days.
UtahChippewa, Pert near any knappable rock will work, even obsidian I rekon. I use gravel because that's my rock source and it is pretty tough stuff too. I've made them from all different types of knappable stone. Actually I've made more plain hooks than jigs, but aint much difference as far as making and using them. The jigs are ready to fish and don't require any thing added to get reactions from fish, where a hook might need some type of bait or attractant added to it.
I've made some how to's in the past but I will do another detailed one and cover some things that I think really help to make it and not break it.