sedimentary
Chert Concretion (Flint)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: tan, brown, white, and gray with concentric banding, Luster: waxy to dull, Structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.65
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: tan, brown, white, and gray with concentric banding, Luster: waxy to dull, Structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed by the precipitation of mineral cement in the spaces between particles in sedimentary rock, often replacing organic matter or following water flow patterns within limestone or chalk beds. Often Cretaceous or Jurassic in age.
Uses & applications
Historical use for tool-making (arrowheads, scrapers) and fire-starting. Currently used in road construction, landscaping, and as a collector's specimen.
Geological facts
The banding seen in this specimen is often caused by rhythmic precipitation of iron oxides and silicates, similar to how agates form. These rounded nodules are often mistaken for fossils or dinosaur eggs.
Field identification & locations
Identify by its waxy luster on broken surfaces, conchoidal (shell-like) fracture, and the fact that it can scratch glass. Common in riverbeds and limestone outcrops.
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