igneous
Basalt with Alteration Crust
Basalt (SiO2 range 45-52%)
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Aphanitic (fine-grained) to vesicular; Specific Gravity: 2.8-3.0
- Hardness
- 6 (Mohs)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Aphanitic (fine-grained) to vesicular; Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the surface of a terrestrial planet or moon. The tan-colored outer layer is likely a weathered rind or a layer of palagonite formed by contact with water.
Uses & applications
Primarily used in construction (crushed stone), as an aggregate in concrete and asphalt, and for high-temperature insulation (stone wool).
Geological facts
Basalt is the most common volcanic rock on Earth and also makes up most of the surface of the Moon and Mars. It is the primary rock type of the oceanic crust.
Field identification & locations
Identified in the field by its dark color, heavy weight compared to other surface rocks, and fine-grained texture. Often found in volcanic regions, oceanic islands, and mid-ocean ridges.
