igneous
Basalt (Porphyritic Basalt)
Extrusive Igneous Rock
Hardness of 6 on the Mohs scale, dark gray to black color, fine-grained groundmass with visible lighter phenocrysts (such as plagioclase feldspar), dull to sub-vitreous luster, dense, specific gravity around 2.8 - 3.0.
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Physical properties
Hardness of 6 on the Mohs scale, dark gray to black color, fine-grained groundmass with visible lighter phenocrysts (such as plagioclase feldspar), dull to sub-vitreous luster, dense, specific gravity around 2.8 - 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity, magnesium- and iron-rich lava flows at or near the Earth's surface. Can occur in various geological eras from the Precambrian to active volcanic zones today.
Uses & applications
Used extensively 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 oceanic crust and is also the primary volcanic rock found on the Moon (forming the dark lunar maria) and Mars.
Field identification & locations
Identified by its dark color, fine-grained texture, and heavier weight compared to sedimentary rocks. Often found in volcanic regions, oceanic islands, and continental flood basalt provinces worldwide.
