igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Matte, Crystal structure: Aphanitic (fine-grained), Specific gravity: 2.8–3.0
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Matte, Crystal structure: Aphanitic (fine-grained), 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 surface of a terrestrial planet or a moon. Most common rock in the Earth's crust.
Uses & applications
Extensively used in construction for aggregate in highway engineering, railroad ballast, and tile flooring. Also used in high-performance insulation (mineral wool).
Geological facts
Basalt is the primary rock type on the seafloor and makes up the majority of the lunar maria on the Moon. Some columns of basalt form perfect hexagonal shapes like Giant's Causeway.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows small holes (vesicles) where gas was trapped during cooling.
