igneous
Basalt Pebble
Extrusive Igneous Rock
Hardness of 6 on the Mohs scale, dark gray to black or brownish color, dull to sub-metamorphic luster, aphanitic (fine-grained) crystal structure with visible vesicular (gas pore) cavities, and specific gravity around 2.8 - 3.0.
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Physical properties
Hardness of 6 on the Mohs scale, dark gray to black or brownish color, dull to sub-metamorphic luster, aphanitic (fine-grained) crystal structure with visible vesicular (gas pore) cavities, and specific gravity around 2.8 - 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity, magnesium- and iron-rich lava exposed at or very near the Earth's surface, typically originating from volcanic eruptions.
Uses & applications
Used widely in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and in the production 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, Mars, and Venus.
Field identification & locations
Easily identified by its dark, heavy, fine-grained nature and sometimes vesicular texture. Often found smoothed into pebbles along beaches and riverbeds due to wave and water action.
