Chert formations, Pindus mountains Greece(source: candiru)
Our ancestors discovered that certain stones were very hard and, when broken, they formed very sharp edges. These were logically used to produce cutting tools such as knife blades, arrowheads, axe heads and scrapers. Geologists have refined classification of these various stones into categories such as flints, cherts, jaspers, chalcedonies, agates, quartz, obsidian, etc. For the purposes of simplicity it is easy to lump them into two broad categories: Flint-like and obsidian.