sedimentary
River Pebble (Brecciated Chert/Siltstone)
Silicon Dioxide (SiO2) with mineral inclusions
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
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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.
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