sedimentary
River Pebble / Chert Pebble
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Brownish-tan, yellowish-brown, dull earthy tones; Luster: Dull to waxy; Structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Brownish-tan, yellowish-brown, dull earthy tones
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Brownish-tan, yellowish-brown, dull earthy tones; Luster: Dull to waxy; Structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed by the weathering, erosion, and water-transport abrasion of quartz-rich rocks or silica-rich sedimentary deposits (chert/flint), rounded over time in riverbeds or marine environments.
Uses & applications
Commonly used in landscaping, river rock decor, aggregate for concrete, aquarium substrate, and as smooth pocket stones or tumbled specimens.
Geological facts
River pebbles get their smooth, rounded shapes from thousands of years of tumbling against other rocks in flowing water, a natural process mimicking a rock tumbler.
Field identification & locations
Identified by its smooth, rounded egg-like shape, hard surface that resists scratching by steel, and uniform microcrystalline matrix. Commonly found along riverbeds, beaches, and glacial gravel deposits.
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