igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 on Mohs scale; Color: Dark grey to black with reddish-brown oxidation; Luster: Dull to earthy; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8-3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black with reddish-brown oxidation
- Luster
- Dull to earthy
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black with reddish-brown oxidation; Luster: Dull to earthy; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the surface of a terrestrial planet or moon. Most basaltic lavas are of Cenozoic to recent age but can be billions of years old.
Uses & applications
Extensively used in construction for aggregate in road base, railroad ballast, and concrete. Also used for high-quality floor tiles and statues.
Geological facts
Basalt is the most common rock type on Earth's crust, making up most of the ocean floor. It is also common on the Moon, Mars, and Venus.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture. Frequently found in volcanic regions or as weathered river cobbles. Look for small vesicles (holes) or rust-colored weathering on the outer surface.
