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,