igneous
Basalt
Basalt (Aphanitic Mafic Igneous)
Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained); Cleavage: None (conchoidal fracture); Specific Gravity: 2.8–3.0
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained); 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 at or very near the Earth's surface. Most basalt found on Earth is from the Cenozoic era, though it has formed throughout geological history.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. It is also used as dimension stone for tiles and in the manufacturing of rock wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus, making it a key component of the terrestrial planets in our solar system.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and very fine-grained texture where individual crystals are not visible to the naked eye. Often found in volcanic fields, oceanic islands, and mid-ocean ridges.
