sedimentary

Chert Pebble

Microcrystalline silica (SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Grey or brownish-grey. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Grey or brownish-grey
Luster: Waxy to dull

Identified May 18, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale. Color: Grey or brownish-grey. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).

Formation & geological history

Formed via the accumulation of siliceous remains of marine organisms or through chemical precipitation in sedimentary basins over millions of years. This specific specimen appears water-worn into a pebble shape.

Uses & applications

Historically used for stone tools and fire-starting. Currently used as road aggregate, in landscaping, or as a tumble-polishing specimen for beginners.

Geological facts

Chert is composed of the same chemical material as quartz but has a much finer grain size. It was a primary material for prehistoric arrowheads due to its sharp conchoidal fracture.

Field identification & locations

Identified by its extreme hardness (scratches glass), waxy appearance, and smooth, rounded surface indicating fluvial or coastal erosion. Commonly found in riverbeds and glacial tills.