sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale), Color: Variegated brown, tan, and reddish, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Identified June 7, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: Variegated brown, tan, and reddish, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Formation & geological history

Formed from the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or through chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds.

Uses & applications

Historically used for stone tools and arrowheads. Currently used as road aggregate, in glass manufacturing, and as decorative landscaping stones.

Geological facts

Because it fractures with extremely sharp edges, chert was one of the most important materials for early human technology (Stone Age tools). Variations include flint, jasper, and chalcedony.

Field identification & locations

Identify in the field by its hardness (scratches glass), waxy feel, and characteristic shell-like (conchoidal) fractures. Common in sedimentary basins worldwide.