sedimentary
River cobble (Greywacke/Sandstone)
Sandstone / Greywacke
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
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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.
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