igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6.0 on Mohs scale; Color: dark grey to black; Luster: dull to sub-metallic; Structure: Fine-grained/aphanitic; Specific gravity: 2.8 - 3.0
- Hardness
- 6
- Color
- dark grey to black
- Luster
- dull to sub-metallic
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Physical properties
Hardness: 6.0 on Mohs scale; Color: dark 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 moon. Occurs frequently in oceanic plates and volcanic hotspots.
Uses & applications
Used primarily in construction for aggregate, road base, concrete, and railroad ballast. Frequently used in industrial stone wool insulation and occasionally for decorative stone masonry.
Geological facts
Basalt is the most common rock type in Earth's crust and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus, making it a key rock for understanding planetary formation.
Field identification & locations
Identify in the field by its dark color, fine-grained texture (crystals not visible to the naked eye), and high density. Commonly found in lava flow regions like the Pacific Northwest or ocean island chains.
