igneous
Basalt
Aphanitic Mafic Volcanic Rock
Hardness: 5-6 (Mohs); Color: Dark grey to black, often weathering to green or brown; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) or vesicular (pitted); Specific Gravity: 2.8-3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to black, often weathering to green or brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to black, often weathering to green or brown; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) or vesicular (pitted); 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. Most common rock type in Earth's crust.
Uses & applications
Extensively used in construction, crushed stone for road base, concrete aggregate, railroad ballast, and high-quality specimens for garden landscaping or aquarium decor.
Geological facts
Basalt also underlies Earth's ocean basins. Most of the basalt on Earth was formed in three environments: oceanic divergent boundaries, oceanic hotspots, and mantle plumes/hotspots beneath continental crust.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture. It often shows 'vesicles' (small holes) where gas was trapped during cooling.
