igneous
Basalt
Basalt (Mafic Igneous Rock)
Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull or sub-metallic; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0; Vesicular or massive texture.
- Hardness
- 6 (Mohs)
- Color
- Dark gray to black
- Luster
- Dull or sub-metallic
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Physical properties
Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull or sub-metallic; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0; Vesicular or massive texture.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (basaltic lava) exposed at or very near the surface of a terrestrial planet or a moon. Most common rock in the Earth’s crust.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Can be used in stone wool insulation and cast basalt liners.
Geological facts
Basalt is the primary rock type on the seafloor. It also makes up prominent features like the Giant's Causeway in Ireland and the Moon's maria (dark plains visible from Earth).
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture which lacks visible crystals. Commonly found in volcanic regions and ocean basins.
