Welcome, and you truly do have some good rock. I'm sure there will be plenty of people willing to start it for you, just kidding.
With a good hammerstone or big billet find a narrow end of the rock and try and knock a piece off at an angle. From there just keep hitting the Cortex at a different angle so you are really just peeling it off.
if you can't get together with a knapper in your area( there are some real good ones where you live), then try to find DC Waldorfs books or check out some of the good videos on YouTube.