sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: light grey to brown/tan, Luster: waxy to dull, Crystal structure: microcrystalline (cryptocrystalline), Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: light grey to brown/tan, Luster: waxy to dull, Crystal structure: microcrystalline (cryptocrystalline), Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the precipitation of silica from groundwater or the accumulation of silica-rich marine microfossils (like radiolaria or diatoms) in limestone or chalk beds. Often Cretaceous or Jurassic in age.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used as road aggregate, architectural stone, and for survival fire-starting.
Geological facts
Flint was one of the first materials traded over long distances by prehistoric humans. When struck against steel, it produces sparks used to ignite gunpowder or fire tinder.
Field identification & locations
Identify in the field by its waxy texture and sharp, shell-like (conchoidal) edges when broken. Commonly found as nodules in chalk or limestone cliffs.
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