igneous
Basalt
Mafic volcanic rock (Basalt)
Hardness: 6 on Mohs scale; Color: Dark grey to black, weathering to brown/red; Luster: Dull to earthy; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8–3.0.
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black, weathering to brown/red
- Luster
- Dull to earthy
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black, weathering to brown/red; Luster: Dull to 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, covering much of the ocean floor and large continental regions.
Uses & applications
Used primarily in construction for crushed stone, road base, concrete aggregate, and railroad ballast. Exceptionally durable varieties are used for floor tiles and landscaping.
Geological facts
Basalt is the primary rock type of the ocean crust. On the Moon, the dark plains known as 'maria' are actually vast plains of basaltic lava flows. It often forms unique hexagonal columns during cooling, known as columnar jointing.
Field identification & locations
Identify in the field by its dark color, heavy weight for its size, and lack of visible crystals to the naked eye. It is commonly found in volcanic regions, oceanic islands like Hawaii, and mid-ocean ridges.
