sedimentary

Chert / Flint

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale. Color: Tan, brown, reddish-orange iron staining, pale green-grey core. Luster: Dull to waxy/vitreous. Conchoidal fracture with sharp edges. Microcrystalline to cryptocrystalline structure. Specific gravity: ~2.65.

Hardness: 7 on Mohs scale
Luster: Dull to waxy/vitreous

Identified July 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed biogenically or chemically in marine environments through the precipitation of silica from microscopic organisms (diatoms, radiolarians) or silica-rich water replacement in limestone/chalk beds.

Uses & applications

Historically used for knapping sharp stone tools, arrowheads, and spark generation in flintlock firearms. Modern uses include road aggregate, crushed stone, and lapidary carving.

Geological facts

Chert has been used by human ancestors for hundreds of thousands of years to craft tools due to its predictable, glass-like conchoidal fracturing.

Field identification & locations

Identify in the field by its extreme hardness (scratches steel), smooth waxy feel on fresh surfaces, and curved conchoidal fractures. Commonly found in limestone outcrops, stream beds, and gravel deposits.