sedimentary
Chert (Flint)
Chert (Cryptocrystalline Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or light brown (as shown); Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or light brown (as shown)
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or light brown (as shown); Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed via the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from silica-rich groundwater within limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges. Modernly used in road construction, as a component in ceramics, and for making fire (flint and steel).
Geological facts
Chert has been used by humans for over 2 million years to make tools. It produces sharp edges that are often more acute than a surgical scalpel.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and its characteristic shell-like (conchoidal) fracture patterns. Found globally in sedimentary rock sequences.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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