sedimentary or metamorphic

River Pebble (likely Quartzite or Chert)

Silicon Dioxide (SiO2) crystal conglomerate

Hardness: 6.5-7 on Mohs scale. Color: Dull tan to greyish-white. Luster: Waxy to dull. Structure: Microcrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.

Hardness: 6
Color: Dull tan to greyish-white
Luster: Waxy to dull

Identified March 17, 2026More sedimentary or metamorphic →

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: Dull tan to greyish-white. Luster: Waxy to dull. Structure: Microcrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.

Formation & geological history

Formed through the smoothing of rock fragments by water erosion over hundreds to thousands of years. Usually originates from high-silica rocks like sandstone or quartz reefs, weathered out of mountains and transported by rivers.

Uses & applications

Commonly used as decorative landscaping stones, aquarium gravel, or as industrial aggregate in construction and concrete. Polished versions are used in basic lapidary work.

Geological facts

River pebbles become rounded due to the process of 'attrition,' where rocks collide with each other in moving water, wearing down sharp edges into smooth, ellipsoidal shapes.

Field identification & locations

Identify by its smooth, water-worn exterior and lack of sharp edges. To definitively identify the mineral, a scratch test against steel (usually leaves no mark) or a fracture test to reveal a waxy interior is used. Found in riverbeds, glacial deposits, and beaches.

Other sedimentary or metamorphic specimens

See all

Shale or Argillite

Shale (sedimentary) / Argillite (metamorphic)

Sedimentary or Metamorphic (low-grade)

Anthracite Coal

Anthracite (Carbon-rich Sedimentary-to-Metamorphic Rock)

metamorphic

Milky Quartz with Iron Inclusions

Quartz (Silicon Dioxide, SiO2)

mineral

Anthracite Coal

Anthracite (Carbon-based sedimentary-derived metamorphic rock)

metamorphic

Jasper Conglomerate (Puddingstone)

Siliceous Conglomerate (Quartz and Jasper clasts in a fine-grained matrix)

sedimentary

River Pebbles and Quartz

Mixed Igneous, Sedimentary, and Metamorphic Rocks (Silicon Dioxide SiO2 dominant)

mixed