sedimentary

River Pebble (Brecciated Chert/Siltstone)

Silicon Dioxide (SiO2) with mineral inclusions

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale), Color: Mottled grey and black with white veining, Luster: Dull to waxy, Crystal Structure: Microcrystalline, Cleavage: None/Conchoidal fracture

Hardness: 6

Identified May 5, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale), Color: Mottled grey and black with white veining, Luster: Dull to waxy, Crystal Structure: Microcrystalline, Cleavage: None/Conchoidal fracture

Formation & geological history

Formed through the accumulation of fine-grained silica or clay minerals, followed by physical fracturing (brecciation) and cementation. This specific piece has been smoothed by water erosion in a fluvial (river) environment.

Uses & applications

Primarily used as decorative landscaping stone, drainage aggregate, and for tumbling by hobbyists. Brecciated varieties are sometimes used in lapidary art.

Geological facts

River pebbles like this can travel hundreds of miles from their source, becoming more rounded and polished the further they go. This specimen shows 'brecciation', which indicates it was once part of a fault zone or area of high geological pressure.

Field identification & locations

Identify by its smooth, water-worn texture and hardness (it will easily scratch glass). Look for these in stream beds, beaches, or glacial till deposits.