igneous
Basalt
Basalt (extrusive volcanic rock)
Hardness: 6 on Mohs scale; Color: Dark gray to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic), sometimes vesicular; Cleavage: None; Specific Gravity: 2.8-3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark gray to black
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark gray to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic), sometimes vesicular; Cleavage: None; 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. It can be found in oceanic crust, volcanic islands, and continental flood basalts.
Uses & applications
Extensively used in construction for road base, concrete aggregate, railroad ballast, and high-quality floor tiles or monuments.
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 for its size, and absence of visible crystals. It is ubiquitous in volcanic regions such as Iceland, Hawaii, and the Pacific Northwest.
