sedimentary
Flint / Chert
Silicon dioxide (SiO2)
AI-generated identification · may be incorrectHardness: 7 (Mohs), Color: Grey, black, or tan, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs), Color: Grey, black, or tan, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed in sedimentary rocks, typically as nodules in limestone or chalk through the replacement of calcium carbonate by silica. Often Cretaceous or Jurassic in age.
Uses & applications
Historically used for tools (knapping), fire-starting (sparking with steel), and construction in flint-walled buildings. Used in high-grade ceramics and chemical industry.
Geological facts
Flint is technically a variety of chert. It was the most important material for early human technology, used to make arrowheads and skinscrapers.
Field identification & locations
Identify by its characteristic conchoidal fracture (curved, shell-like breaks) and sharp edges. Common in coastal areas with chalk cliffs or river beds.
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