igneous
Basalt
Mafic igneous rock (primarily Plagioclase feldspar and Pyroxene)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.9–3.1
- 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: 2.9–3.1
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. Most common rock in Earth's crust, primarily forming the ocean floor.
Uses & applications
Used extensively in construction as aggregate for concrete and asphalt, road base, railroad ballast, and sometimes as a dimension stone for floor tiles or monuments.
Geological facts
Basalt is the most common rock on Earth and also makes up much of the surfaces of the Moon, Mars, and Venus. The Giant's Causeway in Ireland is a famous example of columnar basalt joints.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. Found in volcanic regions and volcanic plateaus globally.
