igneous
Basalt
Aphanitic Mafic Volcanic Rock
Hardness: 6 (Mohs scale); Color: dark gray to black; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic) to vesicular; Specific gravity: 2.8-3.0
- Hardness
- 6 (Mohs scale)
- Color
- dark gray to black
- Luster
- dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: dark gray to black; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic) to vesicular; 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. It covers about 70 percent of Earth's surface.
Uses & applications
Extensively used in construction, especially as crushed stone for road base, railroad ballast, and concrete aggregate. High-quality pieces are used for sculptures and hot stone massage therapy.
Geological facts
Basalt is the most common rock on the Earth's crust and also makes up the lunar maria on the Moon. It is the primary rock type of all ocean basins.
Field identification & locations
Identified in the field by its dark color, heavy weight (relative to size), and fine-grained texture. It often shows columnar jointing in large outcrops.
