igneous
Basalt Pebble
Extrusive Igneous Rock
Hardness: 6 on the Mohs scale, Color: Dark gray to black, Luster: Dull to sub-vitreous, Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific Gravity: 2.8 - 3.0
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Physical properties
Hardness: 6 on the Mohs scale, Color: Dark gray to black, Luster: Dull to sub-vitreous, Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific Gravity: 2.8 - 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 surface of a planet or moon.
Uses & applications
Used in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and sometimes in sculpture or monuments.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's ocean basins and also forms significant volcanic structures on the Moon, Mars, and Venus.
Field identification & locations
Found abundantly in riverbeds and beaches where water action has smoothed it into a pebble; identified by its dark, fine-grained matrix and heavy feel.
