sedimentary
Chert (Jasper/Flint variety)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, and dark bands; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, and dark bands
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, and dark bands; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. Often found as nodules in limestone or chalk.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges; used today as a decorative stone, in construction aggregate, and by flintknappers.
Geological facts
Because of its conchoidal fracture, chert breaks like glass, producing razor-sharp edges. It was the primary material for arrowheads and scrapers in prehistoric times.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, curved fracture surfaces. Found worldwide in sedimentary bedding planes.
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