igneous
River Cobble (Basalt or Sandstone)
Weathered Basalt or Fine-Grained Sandstone
Hardness: 6-7 on Mohs scale; Color: Dark brown, brownish-grey, or dark reddish-brown; Luster: Dull to earthy; Texture: Fine-grained, smoothed and rounded by river abrasion.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark brown, brownish-grey, or dark reddish-brown
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark brown, brownish-grey, or dark reddish-brown; Luster: Dull to earthy; Texture: Fine-grained, smoothed and rounded by river abrasion.
Formation & geological history
Formed through volcanic cooling (if basaltic) or erosion and compaction of sediments (if sandstone), then subsequently rounded over time by water flow in a riverbed or stream environment.
Uses & applications
Used in landscaping, decorative rock arrangements, construction aggregate, or aquascaping.
Geological facts
River rocks owe their smooth, rounded contours to thousands of years of mechanical weathering as flowing water bounces them along stream beds.
Field identification & locations
Look for rounded, smooth edges caused by water erosion, often found in stream beds, riverbanks, or glacial till deposits.
