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FLINT: A hard sedimentary cryptocrystalline form of the mineral quartz. Categorized as a variety of chert. It occurs chiefly as nodules and masses in sedimentary rocks such as chalks and limestones. Inside the nodule, flint is usually dark grey, black, green, white, or brown in color and often has a glassy or waxy appearance. A thin layer on the outside of the nodules is usually different in color, typically white and rough in texture. From a petrological point of view. “Flint” refers specifically to the form of chert which occurs in chalk or marly limestone. Similarly, “common chert” (sometimes referred to simply as “chert”) occurs in limestone.
The exact mode of formation of flint is not as yet clear but it is thought that it occurs as a result of chemical changes in compressed sedimentary rock formations, during the process of diagenesis. One hypothesis is that a gelatinous material fills cavities in the sediment, such as holes bored by crustaceans or molluscs and that this becomes silicified. This theory certainly explains the complex shapes of fllint nodules that are found. The source of dissolved silica in the porous media couldarise from the spicules of silicious sponges. Certain types of flint such as that from the south coast of England, containtrapped fossilised marine flora. Pieces of coral and vegitation have been found preserved like amber inside the flint. Thin slices of the stone often reveal this effect.
