igneous
Basalt
Extrusive igneous rock
Hardness of 6 on the Mohs scale, typically dark gray to black in color, fine-grained aphanitic texture, dull to sub-metallic luster, high specific gravity around 2.8-3.0.
Identified More igneous →
Explore Basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness of 6 on the Mohs scale, typically dark gray to black in color, fine-grained aphanitic texture, dull to sub-metallic luster, high specific gravity around 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron exposed at or very near the surface of a planet or moon.
Uses & applications
Used extensively in construction (crushed stone for road bases, concrete aggregate), railroad ballast, and sometimes in sculpture or architectural tiles.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's ocean basins, and it is also abundantly found on the Moon (forming the lunar maria) and Mars.
Field identification & locations
Easily identified by its dark, fine-grained appearance, heavy weight, and occurrence in volcanic regions as lava flows, columns, or tumbled pebbles.
