While it’s always good practice to carry multiple sharp, modern knives on your hunting, fishing, and camping trips, it’s also nice to have a backup plan, or two, or three. Lucky for us, surgery-sharp, disposable blades are often as close as under our feet. Surprisingly effective blades and tools can be flaked from a variety of stones, including flint, chert, jasper, chalcedony, quartz, and obsidian. That last one is my favorite. Obsidian is a form of volcanic glass common on the west coast and around the Pacific Rim. This shiny stone is capable of breaking into such sharp pieces that the cutting edge can be just one molecule thick in some spots. That’s 25 times sharper than scalpels used in modern surgery. Here’s how to make your own insanely sharp primitive tools.