igneous
Basalt with Phenocrysts
Extrusive Igneous Rock
Hardness of 6 on the Mohs scale, dark gray to black color with lighter mineral flecks, dull to sub-vitreous luster, fine-grained aphanitic groundmass with visible crystals (phenocrysts), 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 with lighter mineral flecks, dull to sub-vitreous luster, fine-grained aphanitic groundmass with visible crystals (phenocrysts), specific gravity around 2.8 to 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity, iron- and magnesium-rich lava flows at or near the Earth's surface.
Uses & applications
Used in construction as crushed aggregate, road base, railroad ballast, and dimension stone.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the oceans and is also abundantly found on the Moon and Mars.
Field identification & locations
Identify in the field by its heavy, dark-colored, fine-grained matrix often containing vesicles or small crystals. Common in volcanic regions worldwide.
