sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Grey, black, or tan; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
- Hardness
- 7 on Mohs scale
- Color
- Grey, black, or tan
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Grey, black, or tan; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
Formation & geological history
Formed in sedimentary environments from the accumulation of silica-rich organic remains or chemical precipitation. Found in limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons (arrowheads); currently used in road construction, concrete aggregate, and fire-starting kits.
Geological facts
Chert was one of the first materials used by early humans for tools because it breaks into very sharp edges. Darker varieties are often called flint.
Field identification & locations
Identify by its waxy luster, hardness (will scratch glass), and distinctive shell-like (conchoidal) curved fractures. Commonly found in riverbeds or coastal cliffs.
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