Most parts of the globe have abundant rocks that can serve as blades, and you don't need to be a geologist to find them. Razor-edged rocks are as close by as the nearest creek, although not all rocks break with a good cutting edge. Flint, chert, jasper, chalcedony, quartz, and obsidian are a few that do. Try the different types of rock in your area to see what works best. There are two ways to get sharp flakes of rock for your stone knife and other tools--bi-polar percussion and direct percussion--and both methods involve striking the stone with a hard hammer rock. For either method, I suggest you wear gloves--preferably made of leather--and protective glasses of some sort.