igneous
Vesicular Basalt (River Pebble)
Basalt (Mafic volcanic rock)
Hardness: 5-6 Mohs. Color: Dark brown to black (wheathered to brown here). Luster: Dull to sub-metallic. Crystal Structure: Aphanitic (fine-grained). Specific Gravity: 2.8–3.0. Features: Vesicular texture with small pits (gas bubbles).
- Hardness
- 5-6 Mohs
- Color
- Dark brown to black (wheathered to brown here)
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 Mohs. Color: Dark brown to black (wheathered to brown here). Luster: Dull to sub-metallic. Crystal Structure: Aphanitic (fine-grained). Specific Gravity: 2.8–3.0. Features: Vesicular texture with small pits (gas bubbles).
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. These specific pebbles were likely rounded by water erosion in a river or coastal environment over thousands of years.
Uses & applications
Commonly used as aggregate in construction, road base, and for landscaping or aquarium decor. Smooth river-worn versions are popular for rock tumbling and decorative stone mulch.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The pits, or vesicles, were once bubbles of gas trapped in the cooling lava.
Field identification & locations
Identify by its dark color, heavy weight (density), and the presence of small holes or 'vesicles'. Found worldwide in volcanic regions, riverbeds, and beaches.
