igneous
Basalt
Mafic extrusive igneous rock
Hardness: 6-7 on Mohs scale. Color: Dark gray to black. Luster: Earthy, dull, or slightly silky. Texture: Fine-grained (aphanitic). Cleavage: None. Specific Gravity: 2.8 - 3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark gray to black
- Luster
- Earthy, dull, or slightly silky
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Dark gray to black. Luster: Earthy, dull, or slightly silky. Texture: Fine-grained (aphanitic). Cleavage: None. Specific Gravity: 2.8 - 3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or moon. Extensively found along oceanic spreading centers.
Uses & applications
Widely used as crushed stone in construction, road base, concrete aggregate, and railroad ballast. Also used as dimension stone, for stone carving, and in basalt fiber insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up most of the oceanic floors. It is also extremely common on the Moon and Mars, forming the dark lunar maria.
Field identification & locations
Identify by its dark charcoal-gray color, heavy weight relative to size, fine-grained mineral texture, and lack of visible quartz crystals. Found in volcanic regions worldwide.
