igneous
Basalt
Basalt (extrusive volcanic rock)
Hardness: 5-6 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None; Specific Gravity: 2.8–3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark gray to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; 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 surface of a terrestrial planet or a moon. Most common rock in the Earth's crust, found in ocean basins and volcanic islands.
Uses & applications
Extensively used in construction, crushed stone for road base, concrete aggregate, railroad ballast, and sometimes in production of stone wool insulation.
Geological facts
Basalt is the most common rock type on the surfaces of Mars, Venus, and the Moon. It makes up the majority of the ocean floor on Earth.
Field identification & locations
Identify by its dark color, heavy weight (dense), and fine-grained texture. It often shows vesicles (gas bubbles). Common in volcanic regions and oceanic plate margins.
