sedimentary
River Pebble (Gravel)
Clastic sedimentary rock (likely Siltstone or Mudstone pebble; SiO2 with various impurities)
Hardness: 6-7 (Mohs scale); Color: Brown, tan, and olive-green; Luster: Dull/Earthy when dry, waxy when wet; Crystal structure: Microcrystalline; Cleavage: None; Specific gravity: Approx 2.6.
- Hardness
- 6-7 (Mohs scale)
- Color
- Brown, tan, and olive-green
- Luster
- Dull/Earthy when dry, waxy when wet
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Brown, tan, and olive-green; Luster: Dull/Earthy when dry, waxy when wet; Crystal structure: Microcrystalline; Cleavage: None; Specific gravity: Approx 2.6.
Formation & geological history
Formed through the erosion and weathering of larger rock formations. These specific specimens are water-worn, having been smoothed by mechanical abrasion in a stream, river, or glacial environment.
Uses & applications
Used primarily in construction (aggregate for concrete), landscaping, road surfacing, and as drainage material.
Geological facts
Pebbles are defined by the Udden-Wentworth scale as rock fragments between 4 and 64 millimeters in diameter. Over time, these can be naturally cemented together to form a rock called conglomerate.
Field identification & locations
Identify in the field by their rounded edges and smooth texture resulting from water transport. They are ubiquitous in riverbeds, floodplains, and coastal areas.
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