sedimentary
Chert (varietal Flint or Jasper)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: yellowish-brown to tan with grey banding; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- yellowish-brown to tan with grey banding
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: yellowish-brown to tan with grey banding; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed by the precipitation of silica in sedimentary environments, often replacing calcium carbonate in limestone or forming nodules through chemical accumulation of silica-rich fluids. It can date back from the Precambrian to recent eras.
Uses & applications
Historically used for stone tools and starting fires; modernly used in road construction, landscape gravel, and occasionally as semi-precious gemstones (Jasper) for jewelry.
Geological facts
Because of its extreme hardness and conchoidal fracture (breaking like glass), it was the primary material for prehistoric arrowheads and spears. Flint is a specific variety of chert used in strike-a-lights.
Field identification & locations
Identify in the field by its smooth, waxy texture and sharp edges when broken. It cannot be scratched by a steel blade. Commonly found in stream beds and areas with limestone outcrops.
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