igneous
Basalt
Extrusive mafic igneous rock
Hardness: 6 (Mohs); Color: Dark gray to black, often with greenish or reddish weathering; Luster: Dull/Matte; Structure: Fine-grained (aphanitic), sometimes vesicular; Specific Gravity: 2.8–3.0
- Hardness
- 6 (Mohs)
- Luster
- Dull/Matte
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Physical properties
Hardness: 6 (Mohs); Color: Dark gray to black, often with greenish or reddish weathering; Luster: Dull/Matte; Structure: Fine-grained (aphanitic), sometimes 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. Most of the Earth's crust is composed of basaltic rock.
Uses & applications
Used primarily in construction as aggregate (crushed stone), for asphalt pavement, railroad ballast, and in the manufacturing of stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust. It also makes up the 'maria' on the Moon (the dark plains visible from Earth) and is prevalent on Mars and Venus.
Field identification & locations
Identify by its heavy weight, dark color, and fine-grained texture. It often shows small holes (vesicles) where gas was trapped. Common in volcanic regions and ocean floor outcrops.
