Flint is a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as a variety of chert.
Quartz is a mineral composed of silicon and oxygen atoms in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2.
Cryptocrystalline is a rock texture made up of such minute crystals that its crystalline nature is only vaguely revealed even microscopically in thin section by transmitted polarized light.
A mineral is a naturally occurring chemical compound, usually of crystalline form and not produced by life processes.
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It occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones.
Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the Earth's surface and within bodies of water.
Limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral, forams and molluscs.
Chalk is a soft, white, porous, sedimentary carbonate rock, a form of limestone composed of the mineral calcite.
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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" occurs in limestone.