sedimentary
Chert (Flint)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: Grey, black, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Grey, black, or brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grey, black, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or by chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges; used as flint for fire-starting; industrial uses in abrasives and road construction.
Geological facts
Flint was one of the most important resources for prehistoric humans. When struck, it breaks into sharp, glass-like shards. It was also critical for flintlock firearms in the 17th through 19th centuries.
Field identification & locations
Identify by its waxy appearance, extreme hardness (it will scratch glass), and conchoidal (shell-like) fracture patterns. It is extremely common in areas with limestone or chalk deposits.
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