igneous
Basalt
Basalt (Igneous Volcanic Rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Cleavage: Non-existent; Specific Gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull/Matte
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Cleavage: Non-existent; 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 Earth's surface. Common in oceanic crust and huge volcanic plateaus.
Uses & applications
Extensively used in construction as aggregate for concrete and asphalt, road base, railroad ballast, and sometimes as dimension stone or floor tiles.
Geological facts
Basalt is the most common rock type in Earth's crust and also identifies the composition of the lunar maria on the Moon and much of the surface of Mars.
Field identification & locations
Identify by its dark color, heavy weight (high density), and very fine-grained texture that lacks visible crystals. Often shows 'vesicles' (gas bubbles) or columnar jointing in the field. Found globally in volcanic regions.
