sedimentary
Cobblestones (Basalt/River Rock)
Polished lithic fragments and rounded pebbles
Hardness: Varies by mineral composition (typically 6-7 on Mohs scale for quartz/basalt mix); Color: Dark gray to black with smooth texture; Luster: Dull to sub-vitreous due to polishing by water or wear; Structure: Rounded, smooth, clastic
- Color
- Dark gray to black with smooth texture
- Luster
- Dull to sub-vitreous due to polishing by water or wear
Identified More sedimentary →
Explore Cobblestones (Basalt/River Rock) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: Varies by mineral composition (typically 6-7 on Mohs scale for quartz/basalt mix); Color: Dark gray to black with smooth texture; Luster: Dull to sub-vitreous due to polishing by water or wear; Structure: Rounded, smooth, clastic
Formation & geological history
Formed through the natural weathering, erosion, and water-transport of various parent rocks (often igneous rocks like basalt or sedimentary rocks like sandstone) in riverbeds or coastal environments, subsequently shaped by human masonry.
Uses & applications
Used primarily in landscaping, paving pedestrian walkways, patios, and historic road construction.
Geological facts
Cobblestones were historically used because they created durable roads for horse-drawn carriages before asphalt and concrete became common. Their rounded shape is the result of continuous abrasion in high-energy water environments.
Field identification & locations
Easily identified by their smooth, rounded, elongated shapes embedded in mortar or soil. Commonly found in riverbeds, beaches, and historic urban pathways.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Quartz pebble
Silicon dioxide (SiO2)
sedimentary
Generic Pebble / Rock Fragment
Lithic fragment / Weathered rock
sedimentary
Fossiliferous Concretion
Septarian Concretion containing Brachiopods/Crinoids
fossil
Sedimentary Sandstone
Arenite (Sedimentary Rock)
sedimentary
Banded Siltstone / Mudstone Pebble
Siltstone / Argillite
sedimentary