igneous
Basalt
Mafic volcanic rock (various silicate minerals)
Hardness: 6 (Mohs scale); Color: Dark gray to black, often weathering to brown; Luster: Dull or earthy; Structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black, often weathering to brown
- Luster
- Dull or earthy
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray to black, often weathering to brown; Luster: Dull or earthy; Structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. It is the most common rock type in the Earth's crust.
Uses & applications
Used extensively in construction as aggregate for roads, railroad ballast, and concrete. It is also used as raw material for stone wool insulation and cast basalt liners.
Geological facts
Basalt is the primary rock of the ocean floors. It is also found on the Moon, Mars, and in large flood basalt provinces on Earth like the Deccan Traps or Columbia River Plateau.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and very fine crystalline structure. Often shows vesicular (bubbly) holes if gases were trapped during cooling.
