Chert (specifically Flint or Common Chert)

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.

Identified on: 4/26/2026

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