sedimentary
Chert (Flint Nodules)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Dark grey to black with a light tan/white weathered rind (cortex), Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark grey to black with a light tan/white weathered rind (cortex), Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal
Formation & geological history
Forms as nodules within sedimentary rocks like limestone or chalk when silica precipitates from groundwater or organic remains. Often found in Cretaceous or Jurassic formations.
Uses & applications
Historically used for stone tools and starting fires; currently used for decorative gravel, landscaping, and lapidary practice.
Geological facts
Flint was used for the first tools of humanity. When struck with steel, it produces sparks used for ignition in flintlock firearms.
Field identification & locations
Identify by the conchoidal fracture (curved, glass-like breaks) and the presence of a white powdery outer crust. Found in chalk cliffs and riverbeds.
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