sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
AI-generated identification · may be incorrectHardness: 7 on Mohs scale; Color: Black, grey, or brown often with a weathered white/tan cortex; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Black, grey, or brown often with a weathered white/tan cortex; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed as nodules or layers in limestone or chalk through the accumulation of siliceous remains of marine organisms like diatoms and radiolarians. The silica precipitates and replaces calcite through diagenesis.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges; modern uses include flintlocks for firearms, road surfacing, and as a raw material in ceramics.
Geological facts
Chert exhibits conchoidal fracture, allowing it to be chipped into extremely sharp blades. It was one of the most important minerals for prehistoric humans during the Stone Age.
Field identification & locations
Identify by its waxy luster on fresh surfaces and glass-like, sharp edges when broken. It will scratch glass but cannot be scratched by a steel knife. Common in limestone outcrops and riverbeds.
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