Flint is 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 colour, and often has a glassy or waxy appearance. A thin layer on the outside of the nodules is usually different in colour, 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 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 flint nodules that are found. The source of dissolved silica in the porous media could arise from the spicules of silicious sponges. Certain types of flint, such as that from the south coast of England, contain trapped fossilised marine flora. Pieces of coral and vegetation have been found preserved like amber inside the flint. Thin slices of the stone often reveal this effect.
Puzzling giant flint formations known as paramoudra and flint circles are found around Europe but especially in Norfolk, England on the beaches at Beeston Bump and West Runton.
Flint sometimes occurs in large flint fields in Jurassic or Cretaceous beds, for example in Europe.
Famous quotes containing the word flint:
“He believes without reservation that Kentucky is the garden spot of the world, and is ready to dispute with anyone who questions his claim. In his enthusiasm for his State he compares with the Methodist preacher whom Timothy Flint heard tell a congregation that “Heaven is a Kentucky of a place.””
—For the State of Kentucky, U.S. public relief program (1935-1943)
“I see you boys of summer in your ruin.
Man in his maggot’s barren.
And boys are full and foreign in the pouch.
I am the man your father was.
We are the sons of flint and pitch.
O see the poles are kissing as they cross.”
—Dylan Thomas (1914–1953)
“Without passion man is a mere latent force and possibility, like the flint which awaits the shock of the iron before it can give forth its spark.”
—Henri-Frédéric Amiel (1821–1881)