igneous
Basalt
Extrusive Igneous Rock
Hardness: 6 on the Mohs scale, Color: Dark gray to black or dark brown, Luster: Dull to sub-aphanitic, Crystal structure: Fine-grained (aphanitic) with microscopic crystals, Cleavage: None, Specific Gravity: 2.8 - 3.0
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Physical properties
Hardness: 6 on the Mohs scale, Color: Dark gray to black or dark brown, Luster: Dull to sub-aphanitic, Crystal structure: Fine-grained (aphanitic) with microscopic crystals, Cleavage: None, Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a planet or moon.
Uses & applications
Used in construction as crushed stone for road bases, aggregate in concrete, railroad ballast, and in the production of rock wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's oceans, and it is also extensively found on the Moon and Mars.
Field identification & locations
Identify by its dark, fine-grained texture, often vesicular (containing gas bubbles) or aphanitic appearance; found worldwide in volcanic provinces and oceanic crusts.
