The thing about that piece that sticks in my mind is the slick/glossy/glassy homogeneity of the material. I imagine that is something that helps make it a good stone to work. Wish I had a week of free time, two pickup loads of this stuff, and a couple of knappers like you, Iowabow, Will H, Tower, Gus, and more to teach me.
Even with all that combined experience and knapping genius, I may still not be able to turn out anything even suitable for driveway fill.