igneous
Basalt
Mafic Volcanic Rock
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) or porphyritic; Cleavage: None; Specific Gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) or porphyritic; 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. It occurs throughout geological time, from the Archean eon to modern volcanic eruptions.
Uses & applications
Used primarily in construction (crushed stone for road bases and concrete aggregate), high-tensile fiber for insulation, and occasionally as structural stone or in landscaping.
Geological facts
Basalt is the most common volcanic rock on Earth and also makes up most of the surface of the Moon and Mars. On Earth, it forms the entirety of the oceanic crust.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture. It often shows small white speckles of plagioclase or green crystals of olivine. Found worldwide in volcanic regions like Hawaii, the Pacific Northwest, and Iceland.
