limestone layer, Buffalo, New York. (3.8 cm wide)]] cliffs, Cape Arkona, Rügen]] flint axe, about 31 cm long]] being struck]] in Kent, England, with walls of flint knapped to show the black inner surface.]]Flint (or flintstone) is a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as a variety of chalcedony or chert. Flint is usually dark-grey, black, or deep brown in colour, and often has a waxy appearance. It occurs chiefly as nodule and masses in sedimentary rocks, such as chalks and limestones.http://www.bbm.me.uk/portsdown/PH_320_Flint.htm The Flints from Portsdown Hillhttp://www.theaaca.com/Learning_Center/flintvs.htm Flint vs Chert Authentic Artefacts Collectors Assn. The exact mode of formation of flint is not yet clear or agreed but it is thought that it occurs as a result of chemical changes in compressed sedimentary rock formations, during the process of diagene