Flint is a type of sedimentary rock caused by diagenesis (chemical change) but doesn't undergo enough heat or compression to morph into a metamorphic rock. This was the rock of choice by Stone Age tool makers since it would splinter into sharp flakes when hit. Later it gave it's name to the flintlock gun which fired when steel would hit a flint edge. The resulting sparks ignited the gun powder. It's also been used for building construction since it weathers well. It has a hardness of 7. This picture is an example of striped flint. Beautiful stuff. One thing about flint is,while you can start a fire w/ it, the rock doesn't like being tossed in a fire (or any excessive heat). It has a tendency to explode.