<P> In Europe, some of the best toolmaking flint has come from Belgium (Obourg, flint mines of Spiennes), the coastal chalks of the English Channel, the Paris Basin, Thy in Jutland (flint mine at Hov), the Sennonian deposits of Rügen, Grimes Graves in England, the Upper Cretaceous chalk formation of Dobruja and the lower Danube (Balkan flint), the Cenomanian chalky marl formation of the Moldavian Plateau (Miorcani flint) and the Jurassic deposits of the Kraków area and Krzemionki in Poland, as well as of the Lägern (silex) in the Jura Mountains of Switzerland . Flint mining is attested since the Palaeolithic, but became more common since the Neolithic (Michelsberg culture, Funnelbeaker culture). </P> <P> When struck against steel, a flint edge produces sparks . The hard flint edge shaves off a particle of the steel that exposes iron, which reacts with oxygen from the atmosphere and can ignite the proper tinder . Prior to the wide availability of steel, rocks of pyrite (FeS) would be used along with the flint, in a similar (but more time - consuming) way . These methods are popular in woodcraft, bushcraft, and amongst people practising traditional fire - starting skills . </P> <P> A later, major use of flint and steel was in the flintlock mechanism, used primarily in flintlock firearms, but also used on dedicated fire - starting tools . A piece of flint held in the jaws of a spring - loaded hammer, when released by a trigger, strikes a hinged piece of steel ("frizzen") at an angle, creating a shower of sparks and exposing a charge of priming powder . The sparks ignite the priming powder and that flame, in turn, ignites the main charge, propelling the ball, bullet, or shot through the barrel . While the military use of the flintlock declined after the adoption of the percussion cap from the 1840s onward, flintlock rifles and shotguns remain in use amongst recreational shooters . </P> <P> Flint and steel used to strike sparks were superseded by ferrocerium (sometimes referred to as "flint", although not true flint, "mischmetal", "hot spark", "metal match", or "fire steel"). This man - made material, when scraped with any hard, sharp edge, produces sparks that are much hotter than obtained with natural flint and steel, allowing use of a wider range of tinders . Because it can produce sparks when wet and can start fires when used correctly, ferrocerium is commonly included in survival kits . Ferrocerium is used in many cigarette lighters, where it is referred to as "flint". </P>

Why are there layers of flint in chalk cliffs