sedimentary

Chert (River Pebble)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs). Color: Variegated brown, tan, and dark grey. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6.

Hardness: 6
Color: Variegated brown, tan, and dark grey
Luster: Dull to waxy

Identified July 5, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs). Color: Variegated brown, tan, and dark grey. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6.

Formation & geological history

Formed from the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. This specific specimen has been smoothed and rounded by water erosion (fluvial transport).

Uses & applications

Primarily used as decorative landscaping stone, aggregate in construction, or for lapidary tumbling. Historically used for stone tools due to its sharp conchoidal fracture.

Geological facts

Chert is so durable that it often survives long after the surrounding rock has eroded away. It is essentially a non-banded form of chalcedony.

Field identification & locations

Identify by its hardness (it will scratch glass), smooth water-worn surface, and lack of visible grains. Common in riverbeds, gravel pits, and glacial till worldwide.