Flint ("Firestone"), tumbled from Ohio, USA

Flint or Firestone ( "wafer") is a rock that is often found in clumps in limestone and is usually brown or gray in color. Such 'lumps' are mentioned in Geology 'concretions'. In the era of the Late Cretaceous deposited vuursteenconcreties are very rich and shape vary from oblong plates to gewei- and bony stones. Flint consists of crypto-crystalline silicon dioxide and a lot of (chemically bound) water. It is a very hard (7 on the Mohs Hardness Scale) clastisch rock that is mainly found in padded dig corridors of crustaceans. In a hard blow on a piece of flint there is often a shell-shaped fracture surface with sharp edges. This is caused by a stress wave in the rock by the impact. The rock is called flint because a stroke can result with a piece of flint on a piece of iron or pyrite in sparks, which, lit with the necessary experience, a dry, flammable material (like a tuft of loose cotton or dried moss, or tinder) can be. The sparks generated by small iron particles that spontaneously oxidize in air with a lot of heat so that the particles glow. In prehistoric times (Neolithic) people made such as the Neanderthals and the Cro-Magnon man stone tools such as scrapers, arrowheads, axes and blades, preferably of this material. To the degree of sophistication of the product, and the techniques used can be estimated quite accurately how old is the subject. Because such utensils as opposed to human and animal tissue, wood and textiles not perish, they are adjacent or not processed bones and potsherds, almost the only trace we have of prehistoric man.