igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull/earthy
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity magnesium-rich and iron-rich lava. It is the most common rock in Earth's crust, primarily composed of the ocean floors.
Uses & applications
Used extensively in construction as an aggregate for roads, railroad ballast, and concrete; also used as a dimension stone and in high-performance insulation (rock wool).
Geological facts
Basalt covers more than 70% of the Earth's surface. It is also found on the Moon, Mars, and Venus, making up the vast majority of the lunar maria (dark plains).
Field identification & locations
Identify by its dark color, heavy weight (density), and lack of visible crystals. It typically has a uniform, fine-grained texture and may contain small vesicles (gas bubbles).
