igneous
Basalt (Vesicular)
Extrusive mafic igneous rock
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Sub-metallic, Structure: Aphanitic (fine-grained) with vesicles (air bubbles), Cleavage: None, Specific Gravity: 2.8-3.0.
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Sub-metallic, Structure: Aphanitic (fine-grained) with vesicles (air bubbles), 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 Earth's surface. This specimen shows a vesicular texture from gas bubbles trapped during cooling.
Uses & applications
Used primarily in construction for aggregate, road base, and railroad ballast. Porous varieties are used in landscaping and as 'lava rocks' for gas grills.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture. Found in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.
