sedimentary
River Cobble (Quartzite or Sandstone)
Arenite or Meta-quartzite (SiO2 composition)
Hardness: 6-7 (Mohs scale); Color: Tan, beige, brown mottling; Luster: Dull/Earthy (unpolished); Structure: Granular/Clastic; Cleavage: None
- Hardness
- 6-7 (Mohs scale)
- Color
- Tan, beige, brown mottling
- Luster
- Dull/Earthy (unpolished)
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Tan, beige, brown mottling; Luster: Dull/Earthy (unpolished); Structure: Granular/Clastic; Cleavage: None
Formation & geological history
Formed through the accumulation of sand-sized grains in a high-energy environment like a riverbed or shoreline, eventually lithified and rounded by aquatic erosion over thousands of years.
Uses & applications
Commonly used in landscaping, as decorative garden stones, or in construction as aggregate. Smooth river stones are also popular for rock painting and decorative indoor displays.
Geological facts
The smooth, rounded shape is the result of 'saltation' and abrasion as the rock was tumbled along a riverbed by flowing water, wearing down all sharp edges.
Field identification & locations
Identify by its rounded, ovoid shape and granular texture. Found worldwide in active or ancient riverbeds, alluvial fans, and coastal regions. It will often scratch glass if it is quartz-heavy.
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Arenite (if sandstone)
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Brown Sandstone (River Rock)
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Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Sandstone
Arenite (primarily SiO2)
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