sedimentary

Chert (Flint)

Chert (SiO2)

Hardness: 7.0 (Mohs); Color: Grey, brown, or white; Luster: Waxy to dull; Crystal structure: Microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8

Hardness: 7
Color: Grey, brown, or white
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 7.0 (Mohs); Color: Grey, brown, or white; Luster: Waxy to dull; Crystal structure: Microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8

Formation & geological history

Formed by the precipitation of silica in sedimentary environments, often from the remains of siliceous organisms like diatoms or radiolarians, or through chemical replacement within limestone.

Uses & applications

Historically used for stone tools and fire-starting; currently used in construction aggregate, road surfacing, and as high-quality decorative river stones.

Geological facts

Chert has been used by humans for millions of years to create sharp-edged tools like arrowheads. When struck against steel, it produces sparks used to start fires.

Field identification & locations

Identify by its extreme hardness (scratches glass), waxy luster on fresh surfaces, and distinctive shell-like (conchoidal) fracture patterns. Frequently found in limestone beds.