igneous
Basalt
Basalt (Mafic Extrusive)
Hardness: 5-6 Mohs. Color: Dark gray to black. Luster: Dull to sub-metallic. Structure: Fine-grained (aphanitic) or porphyritic. Specific gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- Dark gray to black
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 5-6 Mohs. Color: Dark gray to black. Luster: Dull to sub-metallic. Structure: Fine-grained (aphanitic) or porphyritic. Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. Common in oceanic crust and volcanic hotspots.
Uses & applications
Widely used in construction for road base, concrete aggregate, railroad ballast, and high-quality stone pavers.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify in the field by its heavy weight, dark color, and lack of visible large crystals. Often found in volcanic regions or riverbeds as rounded cobbles.
