metamorphic or sedimentary
River Cobble (likely Quartzite or Limestone)
SiO2 (Quartzite dominant) or CaCO3 (Limestone dominant)
Hardness: 7 (if quartzite) or 3 (if limestone); Color: Grey/Tan/White; Luster: Dull to Waxy; Structure: Finely crystalline to microcrystalline; Surface: Smooth, rounded, water-worn.
- Hardness
- 7 (if quartzite) or 3 (if limestone)
- Color
- Grey/Tan/White
- Luster
- Dull to Waxy
Identified More metamorphic or sedimentary →
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Physical properties
Hardness: 7 (if quartzite) or 3 (if limestone); Color: Grey/Tan/White; Luster: Dull to Waxy; Structure: Finely crystalline to microcrystalline; Surface: Smooth, rounded, water-worn.
Formation & geological history
Formed through the smoothing of rock fragments by water transport (abrasion) in rivers or ocean shorelines. Geologically, these can range from millions to billions of years old before being weathered.
Uses & applications
Landscaping, decorative garden stone, construction aggregate, and sometimes used in stone tumbling for hobbyists.
Geological facts
River stones get their smooth shape from 'attrition,' a process where rocks collide into each other in a current, wearing down jagged edges over time.
Field identification & locations
Identify by its smooth, rounded 'egg' shape and lack of sharp edges. Found in riverbeds, glacial tills, and beaches. A simple acid test (vinegar) can determine if it is limestone (it will fizz) or quartzite (no reaction).
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