sedimentary
Chert (Chert / Flint)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, brown, or black; Luster: Dull to waxy; Structure: Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, brown, or black
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, brown, or black; Luster: Dull to waxy; Structure: Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation in marine environments; ages range from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to sharp edges; currently used in construction aggregate, road surfacing, and as a component in glass and ceramics.
Geological facts
Dark-colored chert is often called 'flint' and was the primary material for starting fires and discharging early firearms (flintlocks) because it produces sparks when struck against steel.
Field identification & locations
Identify in the field by its hardness (will scratch glass), smooth shell-like (conchoidal) fracture surfaces, and sharp edges. Commonly found in limestone or chalk beds as nodules or layers.
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