igneous
Basalt
Aphanitic Mafic Igneous Rock
Hardness: 6 (Mohs), Color: Dark grey to blackish-green, Luster: Dull/Earthy, Structure: Fine-grained (Aphanitic), Specific gravity: 2.8-3.0
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Physical properties
Hardness: 6 (Mohs), Color: Dark grey to blackish-green, Luster: Dull/Earthy, 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 exposed at or very near the surface of a terrestrial planet or a moon. Most basalt flows are from the Cenozoic era.
Uses & applications
Commonly used as crushed stone for road base, concrete aggregate, railroad ballast, and for high-quality floor tiles and monuments.
Geological facts
Basalt is the most common rock type in Earth's crust; it also makes up most of the surface of the Moon (the lunar maria) and Mars.
Field identification & locations
Identify by its dark color, heavy weight compared to its size, and fine-grained texture. Often found in volcanic regions, oceanic crust, and plateaus.
