sedimentary

River Pebble (Gravel)

Clastic sedimentary rock (likely Siltstone or Mudstone pebble; SiO2 with various impurities)

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs scale); Color: Brown, tan, and olive-green; Luster: Dull/Earthy when dry, waxy when wet; Crystal structure: Microcrystalline; Cleavage: None; Specific gravity: Approx 2.6.

Hardness: 6-7 (Mohs scale)
Color: Brown, tan, and olive-green
Luster: Dull/Earthy when dry, waxy when wet

Identified April 12, 2026More sedimentary →

Explore River Pebble (Gravel) in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 6-7 (Mohs scale); Color: Brown, tan, and olive-green; Luster: Dull/Earthy when dry, waxy when wet; Crystal structure: Microcrystalline; Cleavage: None; Specific gravity: Approx 2.6.

Formation & geological history

Formed through the erosion and weathering of larger rock formations. These specific specimens are water-worn, having been smoothed by mechanical abrasion in a stream, river, or glacial environment.

Uses & applications

Used primarily in construction (aggregate for concrete), landscaping, road surfacing, and as drainage material.

Geological facts

Pebbles are defined by the Udden-Wentworth scale as rock fragments between 4 and 64 millimeters in diameter. Over time, these can be naturally cemented together to form a rock called conglomerate.

Field identification & locations

Identify in the field by their rounded edges and smooth texture resulting from water transport. They are ubiquitous in riverbeds, floodplains, and coastal areas.