igneous
Basalt
Extrusive volcanic basalt
Hardness: 5-6 Mohs; Color: Black, dark grey, or dark brown; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8–3.0
- Hardness
- 5-6 Mohs
- Color
- Black, dark grey, or dark brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 Mohs; Color: Black, dark grey, or dark brown; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to 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 a moon. It can be found in oceanic crust and continental flood basalt provinces.
Uses & applications
Commonly used in construction for aggregate in asphalt and concrete, road base, railroad ballast, and sometimes as a decorative stone for landscaping or dimension stone for flooring.
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 common on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, fine grain, and high density. It often shows a vesicular texture (small holes from gas bubbles). It is found worldwide in volcanic regions like Hawaii or the Pacific Northwest.
