igneous
Basalt
Basalt (extrusive igneous rock)
Hardness: 6 on Mohs scale; Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: aphanitic (fine-grained); Specific gravity: 2.8-3.0
- Hardness
- 6 on Mohs scale
- Color
- dark grey to black
- Luster
- dull to sub-metallic
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Physical properties
Hardness: 6 on Mohs scale; Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: aphanitic (fine-grained); 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 high-quality stone pavers. It can also be melted into fibers for insulation.
Geological facts
Basalt underlies more of the Earth's surface than any other rock type. Most areas within Earth's ocean basins are underlain by basalt. It is also common on the Moon and Mars.
Field identification & locations
Identified in the field by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. It often breaks with a conchoidal or irregular fracture.
