igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 on Mohs scale; Color: Black, dark grey, or greenish; Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8 - 3.0
- Hardness
- 6 on Mohs scale
- Color
- Black, dark grey, or greenish
- Luster
- Dull or earthy
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Physical properties
Hardness: 6 on Mohs scale; Color: Black, dark grey, or greenish; Luster: Dull or earthy; 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 is the most common volcanic rock on Earth.
Uses & applications
Extensively used in construction for aggregate, road base, concrete, and railroad ballast. Also used as dimension stone for tiles and floorings, and in the production of mineral wool insulation.
Geological facts
Basalt is the primary component of the ocean floor and is also found on the Moon and Mars. It forms unique hexagonal columns when cooled slowly, such as at the Giant's Causeway.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture with occasional small holes (vesicles) or visible crystals. Common in volcanic regions and ocean basins.
