igneous
Basalt
Extrusive mafic igneous rock
Hardness: 6.0; Color: Dark grey to black; Luster: Dull to sub-metallic when wet; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic when wet
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Physical properties
Hardness: 6.0; Color: Dark grey to black; Luster: Dull to sub-metallic when wet; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic) at or near the Earth's surface. Common in oceanic crust and volcanic islands.
Uses & applications
Used in construction for road base, concrete aggregate, railroad ballast, and high-quality stone tiles/countertops.
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.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture. Found commonly on beaches near volcanic activity or oceanic ridges.
