igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6 on Mohs scale; Color: Dark grey to charcoal black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to charcoal black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to charcoal black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); 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.
Uses & applications
Commonly used as crushed stone for road base, railroad ballast, and concrete aggregate. Denser varieties are used for floor tiles and monument stone.
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
Identify by its dark color, heavy weight (relative to size), and fine-grained texture. It often shows rounding when found as stream or beach pebbles.
