igneous
Basalt Pebble
Extrusive Igneous Rock
Hardness of 6 on the Mohs scale, dark gray to black color, fine-grained aphanitic texture, dull to submetallic luster, specific gravity around 2.8 to 3.0
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Physical properties
Hardness of 6 on the Mohs scale, dark gray to black color, fine-grained aphanitic texture, dull to submetallic luster, specific gravity around 2.8 to 3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in iron and magnesium exposed at or very near the Earth's surface.
Uses & applications
Used in construction, aggregate for roads, railroad ballast, and sometimes in landscaping and stone polishing.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the oceans and is also found abundantly on the Moon and Mars.
Field identification & locations
Commonly found in stream beds and beaches where dark, fine-grained volcanic rocks have been naturally tumbled and rounded by water action.
