igneous
Basalt
Basalt (Extrusive Mafic Igneous)
Hardness: 6 (Mohs); Color: dark gray to black; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic); Specific gravity: 2.8–3.0
- Hardness
- 6 (Mohs)
- Color
- dark gray to black
- Luster
- dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs); Color: dark gray to black; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic); 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 Earth's surface. Common in oceanic crust and volcanic regions.
Uses & applications
Used in construction for road base, concrete aggregate, railroad ballast, and sometimes as a decorative stone or for stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the surface of the Moon and Mars.
Field identification & locations
Identified in the field by its dark color, heavy weight compared to other small stones, and very fine-grained texture with no large visible crystals.
