igneous
Basalt Pebble
Extrusive Igneous Rock
Hardness: 6 on the Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often containing microscopic olivine or pyroxene crystals; Specific gravity: 2.8 - 3.0
- Hardness
- 6 on the Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on the Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often containing microscopic olivine or pyroxene crystals; Specific gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity basaltic lava exposed at or very near the Earth's surface, typically originating from volcanic eruptions.
Uses & applications
Commonly used in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and sometimes carved for decorative items or monuments.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins and is also found abundantly on the Moon, Mars, and Venus.
Field identification & locations
Easily identified by its dark, fine-grained appearance and heavy weight. Commonly found along beaches and riverbeds where wave action and tumbling have worn it into smooth pebbles.
