igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
Mohs hardness of 6; dark gray to black color; dull to sub-vitreous luster; fine-grained (aphanitic) texture; composition primarily plagioclase feldspar and pyroxene with occasional olivine.
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Physical properties
Mohs hardness of 6; dark gray to black color; dull to sub-vitreous luster; fine-grained (aphanitic) texture; composition primarily plagioclase feldspar and pyroxene with occasional olivine.
Formation & geological history
Formed from the rapid cooling and crystallization of basaltic lava exposed at or very near the Earth's surface, such as at oceanic ridges, volcanic hotspots, and continental flood basalt regions.
Uses & applications
Widely used as crushed stone for construction aggregate, road base, concrete, railroad ballast, and dimension stone for architectural paving.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up almost the entirety of the ocean floors. It is also extremely abundant on the Moon and Mars (e.g., Olympus Mons).
Field identification & locations
Identify in the field by its heavy weight, dark color, and fine-grained, crystalline texture without visible large crystals. Extremely widespread globally in volcanic terrains.
