igneous
Basalt
Extrusive Igneous Rock (Mafic)
Hardness of 6 on the Mohs scale, typically dark gray to black in color, dull to sub-woody luster, aphanitic (fine-grained) crystal structure, conchoidal to uneven fracture, and 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, dull to sub-woody luster, aphanitic (fine-grained) crystal structure, conchoidal to uneven fracture, and specific gravity around 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium- and iron-rich lava exposed at or very near the Earth's surface, often originating from volcanic eruptions or oceanic crust expansion.
Uses & applications
Widely used in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and in the production of basalt fiber.
Geological facts
Basalt is the most common rock type in the Earth's crust, particularly making up most of the oceanic crust and forming massive geological formations like the Columbia River Basalt Group and the Giant's Causeway in Northern Ireland.
Field identification & locations
Easily identified in the field by its dark color, heavy weight relative to its size, and fine-grained texture where individual mineral crystals are usually invisible to the naked eye. Found globally in volcanic regions.
