igneous
Basalt
Extrusive mafic igneous rock
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull/Matte
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Matte; 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 on Earth's crust.
Uses & applications
Commonly used as aggregate in construction, road base, railroad ballast, and in some decorative stonework or as stone for massage therapy.
Geological facts
Basalt underlies more of Earth's surface than any other rock type. It is the primary component of the oceanic crust and is also found on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture lacking visible crystals. Found worldwide in volcanic regions and ocean floors.
