igneous
Basalt
Basalt (Extrusive Igneous Rock)
Hardness: 5-6 Mohs. Color: dark grey to black. Luster: dull to sub-metallic. Crystal structure: fine-grained (aphanitic). Cleavage: none. Specific gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- dark grey to black
- Luster
- dull to sub-metallic
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Physical properties
Hardness: 5-6 Mohs. Color: dark grey to black. Luster: dull to sub-metallic. Crystal structure: fine-grained (aphanitic). Cleavage: none. 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 on Earth's oceanic crust.
Uses & applications
Used in construction for road base, concrete aggregate, railroad ballast, and dimension stone for floor tiles and monuments.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the lunar maria on the Moon. It was once lava flowing across the surface.
Field identification & locations
Identify by its dark color, heavy weight for its size (high density), and lack of visible crystals to the naked eye. Found worldwide in volcanic regions like Hawaii or the Pacific Northwest.
