igneous
Basalt
Extrusive mafic igneous rock
Hardness: 6 (Mohs scale); Color: Dark gray to black, often with greenish or rusty brown weathering; Luster: Dull to sub-metallic; Structure: Fine-grained/aphanitic; Specific Gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray to black, often with greenish or rusty brown weathering; Luster: Dull to sub-metallic; 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 the surface. Can range from recent formations to billions of years old. Commonly found in oceanic crust and lava flows.
Uses & applications
Used widely in construction for aggregate, road base, railroad ballast, and high-quality concrete. Also used for paving stones and stone sculptures.
Geological facts
Basalt is the most common rock type in Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture. Found near volcanic regions and riverbeds where erosion transports boulders.
