The large rock acts like an anvil, to provide unyielding resistance behind the rock you want to break. You’ll also stand up the rock you want broken on its tallest axis. Make it stand tall, as if you were trying to make an egg stand on its tallest end. Making the rock stand tall is an important part of the process, allowing the shock waves from the hammer stone strike to move through the rock on the most efficient path. Use a large, flat hammer stone to crack down hard on the rock you are breaking. The hammer rock should be 4 to 5 times larger than the rock you are trying to break. If you are lucky, you’ll fracture off some nice, thin, wickedly sharp stone blades within a few strikes. With a little practice, you should be cracking rocks into sharp blades in no time, you’ll be able to predict the outcome of the shape, and also be able to reproduce similar results from different rocks.