igneous
Basalt
Extrusive mafic igneous rock
Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull/Matte
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Physical properties
Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); 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. Often found in oceanic crust and volcanic regions.
Uses & applications
Used primarily in construction for aggregate, road base, and concrete; also used as a thermal insulator in stone wool form and occasionally for stonework and sculptures.
Geological facts
Basalt is the most common rock type on Earth's surface and also covers large areas of the Moon, Venus, and Mars (where it forms the giant volcano Olympus Mons).
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and lack of visible large crystals. Most common in volcanic fields, near faults, and along coastlines with volcanic history.
