igneous
Basalt
Mafic Igneous Rock
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8 - 3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; 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 primarily in construction for aggregate, road base, concrete, and railroad ballast. Also used as dimension stone and for industrial floor tiles.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up the entirety of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture. Found globally in volcanic regions such as Iceland, Hawaii, and the Deccan Traps. Collectors look for vesicles (gas bubbles) often filled with secondary minerals like zeolites.
