igneous
Basalt
Extrusive mafic igneous rock
Hardness: 6; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; 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; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); 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 terrestrial basalt was formed during the Cenozoic era, though occurrences date back billions of years.
Uses & applications
Commonly used as crushed stone for construction projects, road base, railroad ballast, and high-quality concrete aggregate. Sometimes used in polished form for floor tiles or monument carvings.
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 and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows vesicular (bubbly) textures if gases were trapped during cooling. Found globally in volcanic regions and oceanic crust.
