igneous
Basalt
Basalt (Extrusive Igneous Rock)
Hardness: 6; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None/Irregular; Specific Gravity: 2.8-3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None/Irregular; 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 is the most common volcanic rock on Earth.
Uses & applications
Extensively used in construction for road base, concrete aggregate, railroad ballast, and dimension stone for floor tiles and monuments.
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 a large portion of the surface of the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture. It often shows vesiculation (small holes from gas bubbles). Found globally in volcanic regions and oceanic crust.
