igneous
Basalt
Basalt
Hardness: 6.0; Color: Dark grey to black, weathering to brown or rust; Luster: Dull to earthy; Crystal structure: Aphanitic (fine-grained), often vesicular (pits from gas bubbles); Specific gravity: 2.8–3.0
- Hardness
- 6
- Color
- Dark grey to black, weathering to brown or rust
- Luster
- Dull to earthy
Identified More igneous →
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Physical properties
Hardness: 6.0; Color: Dark grey to black, weathering to brown or rust; Luster: Dull to earthy; Crystal structure: Aphanitic (fine-grained), often vesicular (pits from gas bubbles); 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. Found in oceanic crust, volcanic islands (like Hawaii), and large continental flood basalt provinces.
Uses & applications
Extensively used in construction for aggregate, road base, concrete, and railroad ballast. It is also used as a thermal insulator in the form of rock wool.
Geological facts
Basalt is the most common rock type on Earth's surface and also covers large areas of the Moon, Mars, and Venus. The famous Giant's Causeway in Ireland is composed of basalt columns.
Field identification & locations
Identify by its dark color, heavy weight (relative to other surface rocks), and fine-grained texture. It often shows small holes (vesicles) or may have small green crystals of olivine embedded inside. Found globally in volcanic regions.
