sedimentary

River Pebble / Chert Pebble

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

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

Identified July 27, 2026More sedimentary →

Explore River Pebble / Chert Pebble in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

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.