sedimentary

Chert (specifically Flint or Common Chert)

Chert (Cryptocrystalline Silica, SiO2)

AI-generated identification · may be incorrect

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

Identified April 26, 2026More sedimentary →

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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.