sedimentary
River Pebble (Siltstone / Basalt)
Microcrystalline Quartz / Indurated Mudstone / Fine-grained Basalt
Hardness: 5-7 Mohs; Color: Dark olive brown, brownish-green to dark grey; Luster: Waxy to dull smooth polish; Texture: Aphanitic, ultra-fine-grained; Specific Gravity: 2.5-2.9
- Hardness
- 5-7 Mohs
- Color
- Dark olive brown, brownish-green to dark grey
- Luster
- Waxy to dull smooth polish
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Physical properties
Hardness: 5-7 Mohs; Color: Dark olive brown, brownish-green to dark grey; Luster: Waxy to dull smooth polish; Texture: Aphanitic, ultra-fine-grained; Specific Gravity: 2.5-2.9
Formation & geological history
Formed via erosion and mechanical weathering of fine-grained sedimentary mudstone or volcanic mafic rocks. The teardrop/kidney bean shape is created by natural water abrasion in riverbeds or coastal wave action.
Uses & applications
Commonly collected as smooth worry stones, used in landscaping, rock tumbling, or decorative aquarium gravel.
Geological facts
River pebbles acquire their smooth, rounded contours over decades or centuries of saltation, sliding, and tumbling against other stones along high-energy water currents.
Field identification & locations
Identify by its smooth water-worn surface, lack of visible macroscopic crystals, teardrop pebble shape, and dull to waxy luster. Found along riverbanks, streams, and beaches globally.
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