sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Black, grey, dark blue; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Black, grey, dark blue
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: Black, grey, dark blue; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of microscopic silica-rich organisms (like diatoms or radiolarians) or chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires; modernly used in road construction, ceramics, and as decorative gravel.
Geological facts
Dark-colored chert is specifically called Flint. It was the primary material for the Stone Age tool revolution due to its predictable conchoidal fracturing which creates razor-sharp edges.
Field identification & locations
Identify by its waxy texture, extreme hardness (it will scratch glass), and its characteristic shell-like (conchoidal) fracture patterns when broken.
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