sedimentary

River cobble (Greywacke/Sandstone)

Sandstone / Greywacke

AI-generated identification · may be incorrect

Hardness: 6-7 on Mohs scale. Color: Dull grey, brownish-tan with dark inclusions/veins. Luster: Earthy to dull. Texture: Fine to medium-grained, rounded by stream erosion.

Hardness: 6-7 on Mohs scale
Color: Dull grey, brownish-tan with dark inclusions/veins
Luster: Earthy to dull

Identified July 23, 2026More sedimentary →

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Physical properties

Hardness: 6-7 on Mohs scale. Color: Dull grey, brownish-tan with dark inclusions/veins. Luster: Earthy to dull. Texture: Fine to medium-grained, rounded by stream erosion.

Formation & geological history

Formed through the compaction and cementation of mineral grains and rock fragments in aquatic environments, followed by physical weathering and erosion in stream beds.

Uses & applications

Commonly used as construction aggregate, landscaping river rock, fill material, or as basic decorative rocks for gardens.

Geological facts

River cobbles are shaped by abrasion against other rocks and sand in flowing water over thousands of years, resulting in smooth, rounded edges.

Field identification & locations

Identify by its smooth, water-worn outer shape combined with fine-grained sandy or silty texture inside. Commonly found along riverbanks, lakeshores, and glacial deposits worldwide.