igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6; Color: Dark grey to black; Luster: Dull to submetallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None; Specific gravity: 2.8-3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull to submetallic
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Physical properties
Hardness: 6; Color: Dark grey to black; Luster: Dull to submetallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None; 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 basalt on Earth was formed by volcanic activity at mid-ocean ridges or hot spots.
Uses & applications
Extensively used in construction for road base, concrete aggregate, and railroad ballast. Denser varieties are used for high-quality floor tiles and monuments.
Geological facts
Basalt is the most common rock type in Earth's crust and makes up most of the ocean floor. It is also the primary rock covering large areas of the Moon, Mars, and Venus (the Lunar Maria).
Field identification & locations
Identified in the field by its dark color, heavy weight compared to its size, and fine-grained texture. It often weathers to a reddish-brown color due to oxidation of iron content. Common in volcanic regions and coastal areas near seafloor spreads.
