igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6 (Mohs scale), Color: Dark grey to black or greenish-black, Luster: Dull to sub-metallic, Structure: Fine-grained/aphanitic with some vesicles or phenocrysts, Cleavage: None
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to black or greenish-black, Luster: Dull to sub-metallic, Structure: Fine-grained/aphanitic with some vesicles or phenocrysts, Cleavage: None
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 moon. Occurs throughout geological time from Precambrian to present.
Uses & applications
Extensively used in construction for road base, concrete aggregate, railroad ballast, and dimension stone for buildings. Also used as stone wool for insulation.
Geological facts
Basalt is the most common rock type on Earth's crust and makes up most of the ocean floor. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (high specific gravity), and very fine-grained texture. Commonly found in volcanic fields, oceanic islands, and mid-ocean ridges.
