igneous
Basalt Pebble
Basalt (Extrusive Igneous Rock)
Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0.
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the surface of a terrestrial planet or a moon. This specimen appears water-worn into a pebble shape.
Uses & applications
Large scale basalt is used for crushed stone in construction, road base, and concrete aggregate. Individual pebbles are used for landscaping, aquariums, and decorative paving.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify in the field by its dark color, heavy weight for its size, and very fine-grained texture. Commonly found in volcanic regions or riverbeds downstream from volcanic sources.
