igneous
Basalt
Extrusive mafic igneous rock
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None (conchoidal fracture); Specific gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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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; Cleavage: None (conchoidal fracture); 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 moon. Basalt comprises more than 90% of all volcanic rock on Earth.
Uses & applications
Extensively used in construction, specifically as aggregate for roads, railroad ballast, and concrete. It is also used as dimension stone for tiles and floorings, and crushed for industrial high-temperature insulation.
Geological facts
Basalt is the most common rock type on Earth's crust and makes up most of the ocean floor. Large-scale eruptions of basalt can create 'Large Igneous Provinces' and it is the primary rock found on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture which lacks visible crystals to the naked eye. Often found in volcanic regions, oceanic islands, and mid-ocean ridges.
