igneous
Basalt
Basalt
Hardness: 6.0; Color: dark grey to black; Luster: dull to submetallic; Crystal structure: fine-grained (aphanitic); 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: 6.0; Color: dark grey to black; Luster: dull to submetallic; Crystal structure: fine-grained (aphanitic); 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. Common in oceanic crust and volcanic islands.
Uses & applications
Used widely in construction for road base, concrete aggregate, asphalt pavement aggregate, railroad ballast, and filter stone in drain fields.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor. It also exists on other planetary bodies like Mars and the Moon.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture. It often weathers to a reddish-brown color due to high iron content.
