sedimentary
Stream Pebble (Chert / Jasper)
Microcrystalline Quartz (SiO2)
Hardness 6.5-7 on Mohs scale; dark reddish-brown to dark gray color; sub-vitreous to waxy luster when wet; cryptocrystalline structure; smooth, well-rounded river-worn shape.
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Physical properties
Hardness 6.5-7 on Mohs scale; dark reddish-brown to dark gray color; sub-vitreous to waxy luster when wet; cryptocrystalline structure; smooth, well-rounded river-worn shape.
Formation & geological history
Formed through the accumulation of silica-rich fluids or radiolarian/diatomaceous ooze on the sea floor, followed by compaction and lithification. Later eroded and rounded by stream or river water transport.
Uses & applications
Commonly collected as river stones, used in landscaping, polished in rock tumblers for lapidary crafts, or used historically for knapping flint tools.
Geological facts
River pebbles become smooth and rounded due to mechanical attrition as they tumble downstream over years, decades, or millennia.
Field identification & locations
Look for rounded, smooth shapes along gravel bars, riverbeds, and ocean beaches. Extremely durable due to high quartz content.
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