igneous
River Pebble (Basalt or fine-grained Quartzite)
Fine-grained Mafic Rock (Volcanic Basalt)
Hardness: 6-7 on Mohs scale; Color: Dull grey to charcoal; Luster: Matte when dry, waxy when wet; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.7-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Dull grey to charcoal
- Luster
- Matte when dry, waxy when wet
Identified More igneous →
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dull grey to charcoal; Luster: Matte when dry, waxy when wet; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.7-3.0.
Formation & geological history
Formed from cooled lava (if basalt) or compressed sand crystals (if quartzite). This specific specimen has been smoothed by fluvial (river) erosion over thousands of years.
Uses & applications
Commonly used in landscaping, construction aggregate, and as 'worry stones' or for aquarium decor.
Geological facts
The rounded shape indicates that this rock has traveled many miles in moving water, which acts as a natural tumbler to wear down sharp edges.
Field identification & locations
Identify by its rounded, smooth texture and lack of visible large crystals. Commonly found in riverbeds, glacial tills, and coastal beaches.
