sedimentary
Chert (specifically Flint or Common Chert)
Chert (Cryptocrystalline Silica, SiO2)
Hardness: 7 (Mohs scale); Color: Gray, tan, white, or brown; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, white, or brown
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, tan, white, or brown; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater. Found in sedimentary environments, often as nodules in limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used in construction aggregate, road surfacing, and as a component in ceramics.
Geological facts
Chert has a conchoidal fracture, meaning it breaks like glass to create extremely sharp edges. It was one of the most important minerals for early humans for survival and tool-making.
Field identification & locations
Identify it by its extreme hardness (will scratch glass), waxy luster on fresh surfaces, and smooth, curved (conchoidal) break patterns. Very common in many riverbeds and outcroppings worldwide.
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