igneous
Basalt
Extrusive mafic igneous rock
Hardness: 6-7 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) or vesicular; Specific gravity: 2.8–3.0.
- Hardness
- 6-7 (Mohs)
- Color
- Dark gray to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) or 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 Earth's surface. Common in oceanic crust and volcanic regions.
Uses & applications
Used extensively in construction as crushed stone for road base, concrete aggregate, and railroad ballast. Also used as dimension stone for tiles and landscape features.
Geological facts
Basalt is the most common rock on Earth's surface and also covers large areas of the Moon (the lunar maria) and Mars.
Field identification & locations
Field ID: Look for dark color, heavy weight (dense), and fine-grained texture. It may contain small holes called vesicles or form hexagonal columns. Common in oceanic islands like Hawaii or Iceland.
