sedimentary
River Pebble (Quartzite/Siltstone)
Clastic Sedimentary Rock / Quartzite
Hardness: 6-7 (Mohs); Color: Tan, beige, or brownish-grey; Luster: Dull to earthy; Texture: Fine-grained and water-worn; Structure: Rounded clast with no visible cleavage.
- Hardness
- 6-7 (Mohs)
- Color
- Tan, beige, or brownish-grey
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Tan, beige, or brownish-grey; Luster: Dull to earthy; Texture: Fine-grained and water-worn; Structure: Rounded clast with no visible cleavage.
Formation & geological history
Formed from the lithification of silt or sand-sized grains, later rounded by mechanical weathering in a high-energy aquatic environment such as a riverbed or shoreline. These rocks can date back to any geological era from the Paleozoic to the Cenozoic.
Uses & applications
Common pebbles are used as aquarium gravel, in landscaping, as decorative mulch, in construction aggregate, and occasionally for rock tumbling by hobbyists.
Geological facts
The rounding of the stone is a result of a process called 'abrasion' or 'attrition,' where rocks collide with each other in moving water, wearing down sharp edges over hundreds or thousands of years.
Field identification & locations
Identify by its smooth, rounded exterior and fine-grained texture. It will not scratch easily with a steel knife if it is quartz-rich. Found globally in stream beds, beaches, and glacial deposits.
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