sedimentary

Grey River Pebble (Greywacke / Basalt)

Stream-rounded silicate rock pebble

Hardness: 6-7 on Mohs scale. Color: Dark grey with faint white veinings. Luster: Dull to sub-vitreous when dry. Structure: Fine-grained, microcrystalline to clastic matrix. Cleavage: None (conchoidal to uneven fracture).

Hardness: 6-7 on Mohs scale
Color: Dark grey with faint white veinings
Luster: Dull to sub-vitreous when dry

Identified July 24, 2026More sedimentary →

Explore Grey River Pebble (Greywacke / Basalt) in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

Formed through the erosion, mechanical weathering, and stream transport of fine-grained sedimentary rock (like greywacke or shale) or fine-grained igneous rock (like basalt). The rounded shape is caused by natural water attrition over time.

Uses & applications

Commonly used in landscaping, river rock gardens, aquarium decor, and aggregate in construction.

Geological facts

Smooth pebbles like this are natural indicators of ancient or present watercourses, such as rivers, streams, and beaches, where water flow naturally grinds sharp rock fragments into smooth oval shapes.

Field identification & locations

Identify in the field by its smooth, water-worn exterior, rounded edges, and uniform fine-grained grey texture with fine calcite or quartz veinlets. Commonly found along riverbanks, gravel bars, and coastal beaches.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sedimentary Sandstone

Arenite (Sedimentary Rock)

sedimentary

Fossiliferous Concretion

Septarian Concretion containing Brachiopods/Crinoids

fossil

Shale

Shale (clastic sedimentary rock)

sedimentary

Shale

Argillaceous sedimentary rock

sedimentary

Mudstone

Argillite / Siliciclastic sedimentary rock

sedimentary