metamorphic
River Pebble (Likely Quartzite or Chert)
Quartzite (primarily SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Grayish-green to olive; Luster: Waxy to dull (tumbled); Crystal structure: Microcrystalline; Cleavage: None; Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Grayish-green to olive
- Luster
- Waxy to dull (tumbled)
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Grayish-green to olive; Luster: Waxy to dull (tumbled); Crystal structure: Microcrystalline; Cleavage: None; Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, then naturally weathered and smoothed by water transport in a river or coastal environment.
Uses & applications
Common river stones are used for decorative landscaping, aquarium substrate, and as 'worry stones' or for rock tumbling hobbies.
Geological facts
The rounded, smooth shape is known as 'sphericity' and 'roundness' in sedimentology, indicating it has traveled a long distance from its source rock by water flow.
Field identification & locations
Identify in the field by its smooth, water-worn surface and extreme hardness (cannot be scratched by a steel knife). Commonly found in riverbeds, glacial tills, and beaches.
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