sedimentary
Chert (Flint variety)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Dark brown to black, Luster: Waxy to vitreous, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Dark brown to black, Luster: Waxy to vitreous, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)
Formation & geological history
Formed by the accumulation of siliceous remains of organisms or chemical precipitation from silica-rich groundwater within sedimentary beds.
Uses & applications
Used historically for stone tools and fire-starting; currently used in construction aggregates and occasionally as a laboratory abrasive.
Geological facts
Because of its conchoidal fracture, it was the primary material for spearheads and arrowheads during the Stone Age. It produces sparks when struck against steel.
Field identification & locations
Look for a smooth, waxy texture and sharp, shell-like (conchoidal) edges where broken. Commonly found in limestone and chalk deposits.
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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