igneous
Basalt
Mafic extrusive igneous rock
Mohs hardness 6, dark gray to black or brownish-black color, dull to earthy luster, fine-grained (aphanitic) microcrystalline structure, poor cleavage, density approximately 2.8-3.0 g/cm³.
Identified More igneous →
Explore Basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Mohs hardness 6, dark gray to black or brownish-black color, dull to earthy luster, fine-grained (aphanitic) microcrystalline structure, poor cleavage, density approximately 2.8-3.0 g/cm³.
Formation & geological history
Formed from the rapid cooling of low-viscosity magnesium-rich and iron-rich lava exposed at or very near the Earth's surface or ocean floor.
Uses & applications
Widely used in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and dimension stone for paving.
Geological facts
Basalt makes up over 90% of all volcanic rock on Earth and forms almost the entirety of the oceanic crust. It is also extremely common on the Moon and Mars.
Field identification & locations
Identified by its fine-grained texture, dark color, and high density. Found worldwide in volcanic terrains such as oceanic ridges and continental flood basalt regions.
