sedimentary
Banded Chert (likely Flint or Jasper variety)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Dark grey-green with brown bands, Luster: Waxy to dull, Crystal Structure: Microcrystalline/Cryptocrystalline (trigonal system), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Dark grey-green with brown bands, Luster: Waxy to dull, Crystal Structure: Microcrystalline/Cryptocrystalline (trigonal system), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation within sedimentary rock layers, often from ancient marine environments during various geological eras from Precambrian to Cenozoic.
Uses & applications
Used historically for stone tools due to its sharp conchoidal fracture. Modern uses include decorative gravel, tumbled stones for jewelry, and lapidary art.
Geological facts
Banded chert was one of the most important materials for early humans to strike sparks for fire and create arrowheads. The banding represents changes in mineral content during deposition.
Field identification & locations
Identify by its waxy appearance, smooth water-worn surface, and extreme hardness (cannot be scratched by a steel knife). Common in riverbeds and coastal regions where sedimentary layers erode.
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