igneous
Basalt
Extrusive Igneous Rock (Mafic)
Hardness of 6 on the Mohs scale, typically dark gray to black in color, dull to sub-vitreous luster, fine-grained aphanitic crystal structure, lacks prominent cleavage, and has a higher specific gravity due to high iron and magnesium content.
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Physical properties
Hardness of 6 on the Mohs scale, typically dark gray to black in color, dull to sub-vitreous luster, fine-grained aphanitic crystal structure, lacks prominent cleavage, and has a higher specific gravity due to high iron and magnesium content.
Formation & geological history
Formed by the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a planet or moon, often associated with volcanic activity and oceanic crust formation.
Uses & applications
Commonly used 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 crust underlying the world's oceans, and it is also abundantly found on the Moon (forming the lunar maria) and Mars.
Field identification & locations
Easily identified in the field by its dark color, heavy weight relative to its size, and very fine-grained texture where individual mineral crystals are usually microscopic.
