Flint knapping is actually a very precise skill, whether it's done with two stones or by flaking chips off with a piece of antler. The result can be a very, very sharp tool, as sharp as a surgeon's scalpel. Volcanic glass, or obsidian, can be made that sharp rather easily; it can even be ground rather than chipped. In any case, creating weapons and tools out of stone is not done by "banging the rocks together," nor is using flint to create sparks for a fire.

You might want to visit the old flint mines in East Anglia (as I have) to learn more on this subject. It's really quite interesting.