igneous
Basalt
Extrusive mafic igneous rock
Hardness: 6-7 on Mohs scale; Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic) or porphyritic; Specific gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- dark grey to black
- Luster
- dull to sub-metallic
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Physical properties
Hardness: 6-7 on Mohs scale; Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic) or porphyritic; 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 moon. It is the most common volcanic rock on Earth.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and concrete. Also used for high-quality floor tiles and as a decorative stone.
Geological facts
Basalt underlies more of Earth's surface than any other rock type. Most areas within Earth's ocean basins are underlain by basalt. It also makes up the vast majority of the lunar maria on the Moon.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture. It often shows vesification (holes from gas bubbles). Common in volcanic regions like Hawaii or the Pacific Northwest.
