igneous
Basalt
Basalt
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8-3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; 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 is the most common volcanic rock on Earth.
Uses & applications
Extensively used in construction for road base, aggregate, and railroad ballast. Also used in high-end pavers, tiles, and as a raw material for stone wool insulation.
Geological facts
Basalt is equivalent to Gabbro in chemical composition, but Basalt is extrusive (fine-grained) while Gabbro is intrusive (coarse-grained). It covers much of the ocean floor and is found on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture with occasional small holes (vesicles) or visible crystals (phenocrysts). Common in volcanic regions like Hawaii or the Pacific Northwest.
