igneous
Basalt
Extrusive Igneous Rock
Hardness of 6 on the Mohs scale, typically dark gray to black in color, aphanitic (fine-grained) texture, dull luster, specific gravity around 2.8-3.0.
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Physical properties
Hardness of 6 on the Mohs scale, typically dark gray to black in color, aphanitic (fine-grained) texture, dull luster, specific gravity around 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 (crushed stone for road base, concrete aggregate), railroad ballast, and sometimes in the manufacture of stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's oceanic crust and is also found abundantly on the Moon and Mars.
Field identification & locations
Identify by its dark, fine-grained appearance, often vesicular if gas bubbles were trapped during cooling. Found worldwide in volcanic provinces and ocean floors.
