First, bang two simliar stones together. What sound did it make?
Thud. Soft stone.
Best for: sanding, abrading, and filing
Sharp crack. Hard rock.
Best for: hammering, digging
Crisp ring.Very hard rock.
Best for: cutting, slicing, weaponry
Make crude tools
Soft or hard, any rock can be used to file sticks sharp. The simplest way to manufacture tools is to take a hard stone and throw it against a rock face or boulder (shield your eyes). Search the debris for anything with a good edge.
Make better tools
Practiced campers can knap very hard stones (like flint) into effective blades and scrapers. Start with a crude edge (see above). Hold the edge parallel to the ground and hit a hard, rounded stone straight-down against it. Follow through. Tiny chips of rock will fall off the bottom of the edge, honing it.
Sharpen your knife
Collect a palm-size river stone, spit on it, and drag your knife blade against it in a smooth, arcing motion away from you. Hold the blade at a 20-degree angle for maximum sharpness.
Use a hardwood club to drive a large, wedge-shaped rock into a log.
Pile stones into cairns to help ground crews positively identify your track.
Place larger rocks (softball- to football-size) in your fire and let them heat through (at least 30 minutes). Transport them (by rolling or holding with two sticks) into your floorless shelter for a space heater. Two cautions: Never use river stones—they might explode if heated—and don’t let the rocks superheat or they may accidentally ignite any woody materials around them.