igneous
Basalt Pebble
Mafic Extrusive Igneous Rock
Hardness: 6 on Mohs scale. Color: Dark gray to black, often weathered. Luster: Dull to earthy. Texture: Fine-grained (aphanitic). Density: High specific gravity (~2.8 - 3.0).
- Hardness
- 6 on Mohs scale
- Color
- Dark gray to black, often weathered
- Luster
- Dull to earthy
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Physical properties
Hardness: 6 on Mohs scale. Color: Dark gray to black, often weathered. Luster: Dull to earthy. Texture: Fine-grained (aphanitic). Density: High 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 Earth's surface. Commonly smoothed and rounded by river, stream, or beach erosion over time.
Uses & applications
Basalt is extensively used in construction as crushed stone for road bases, concrete aggregate, and railroad ballast. Smooth river pebbles are popular for landscaping, aquariums, and decorative gardens.
Geological facts
Basalt is the most common rock type in the Earth's crust, forming the vast majority of the ocean floor. It is also extremely common on the Moon and Mars.
Field identification & locations
Identified by its smooth, water-worn shape, dark color, and dense, fine-grained texture with no visible individual crystals to the naked eye. Commonly found along riverbeds, lakeshores, and ocean beaches worldwide.
