sedimentary

River Cobble (Sandstone)

Arenite (primarily SiO2)

AI-generated identification · may be incorrect

Hardness: 6-7 Mohs; Color: Tan, brown, or grey with green algae staining; Luster: Dull to earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific gravity: 2.2-2.8

Hardness: 6-7 Mohs
Color: Tan, brown, or grey with green algae staining
Luster: Dull to earthy

Identified June 26, 2026More sedimentary →

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Physical properties

Hardness: 6-7 Mohs; Color: Tan, brown, or grey with green algae staining; Luster: Dull to earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific gravity: 2.2-2.8

Formation & geological history

Formed from the accumulation and cementation of mineral particles or rock fragments of sand size, typically in riverbeds, lakes, or oceans. This specific specimen has been rounded by fluvial (water) erosion.

Uses & applications

Primarily used in construction aggregate, landscaping, road base, and occasionally for architectural stone veneer if large enough and decorative.

Geological facts

Sandstone makes up about 20-25% of all sedimentary rocks on Earth. The green coloring on the surface is likely organic algae growth rather than mineral content, common in riparian environments.

Field identification & locations

Identify in the field by its gritty 'sandpaper' feel and visible grains. Commonly found in riverbeds, glacial tills, and outcrops. Check for layering (bedding planes) if the rock is broken.