igneous
Basalt
Basalt (extrusive volcanic rock)
Hardness: 6 on Mohs scale; Color: charcoal grey to black; Luster: dull to sub-metallic; Structure: fine-grained (aphanitic); Specific gravity: 2.8-3.0
- Hardness
- 6 on Mohs scale
- Color
- charcoal grey to black
- Luster
- dull to sub-metallic
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Physical properties
Hardness: 6 on Mohs scale; Color: charcoal grey to black; Luster: dull to sub-metallic; Structure: fine-grained (aphanitic); 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 basalt flows are from the Cenozoic era, though it has formed throughout Earth's history.
Uses & applications
Extensively used in construction (crushed stone for road base, concrete aggregate, railroad ballast), as thermal insulation (rock wool), and in sculptures or 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
Identified in the field by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. Often found in volcanic regions, oceanic islands (like Hawaii), and flood basalt provinces.
