igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal 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. Most common rock type in the Earth's crust (oceanic crust).
Uses & applications
Used in construction as aggregate (crushed stone) for road base, railroad ballast, and concrete; also used as a dimension stone for flooring and pavers.
Geological facts
Basalt is the most common rock in the Earth's crust and also makes up the lunar maria on the Moon. It often forms striking hexagonal columns when cooling slowly, like at the Giant's Causeway.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and lack of visible crystals without a magnifying lens. It is common in volcanic regions and along riverbeds downstream from volcanic sources.
