To me, the inspiration to practice wilderness survival skills is based in an ideology of minimalism. The less gear you bring, the more intimate of an experience you will have with the earth... both physically and spiritually. Going with less also means that you can't rely on your gear as a safety net of comfort... rather you must be creative and find new solutions in order to thrive. If you have ever used stone tools to create a bow drill set, you know exactly what I am talking about. The experience can be tedious, but the reward is a profound feeling of satisfaction and an incredibly enhanced ability to use a modern knife.
Some areas are abundant with rocks that are good for making blades... others are completely lacking. Do some research in your area to find where the rocks hide. For me, being in the Midwest, I know that creeks tend to be loaded with quality rocks that make excellent blades. It isn't nearly as important to know the type of rocks that are good as it is know the qualities that make good rocks. If you clack the rocks together and they make a ringing sound or they sound like glass... that is a very good thing! Also, be sure to grab rocks that are relatively large because most of them will have a weathered outer surface called the cortex. The bigger the rock, the more quality material there will be under the cortex.
The hammer stone
A hammer stone is a medium sized rock with a rounded surface. This will be used for striking off the blades. The more spherical this rock is, the better.
Now before you start whacking... let's have a little physics lesson. Force travels through rock in a very specific way: when direct impact is made, the energy travels through in a cone shape and it breaks the rock in the same way that a BB from a gun breaks a window. When the hammer stone strikes the edge of the rock, the force will break a blade out from the bottom of the rock. The solid lines in this picture represent the concoidal fracture paths, and the dashed lines represent the stone and the arching path of the hammer stone. If you want to understand this more intuitively, see the video and then go smack some rocks together.
Rest the rock on your thigh and then smack the edge of it with the hammer stone. The hammer stone should glance the edge and it should be swung in a motion such that it follows through and does NOT stop on impact. You may also hold the rocks in midair if it gets to be too painful on the thigh.
If done properly your blades will chip out like the ones in this picture. It is possible to get much larger blades if using a bigger piece of material.
Special grip for carving
Unlike an ordinary knife, the stone blade works best if held very close to the body and pulled in a slicing motion. This will protect the fragile edge from chipping and breaking.
A sharpened stick
For this article, I sharpened a stick to demonstrate the effectiveness of the stone blade. You will be amazed at how well a piece of rock can carve if used properly. The most important thing is to never stop experimenting. There are a multitude of different rocks, striking techniques, and carving techniques to be learned. Get out there and start clacking rocks together! If nothing else, I promise you will feel superhuman when you pick up a modern knife again!