igneous
Basalt
Extrusive igneous rock
Hardness of 5-6 on the Mohs scale, typically dark gray to black in color, aphanitic (fine-grained) texture, dull to submetallic luster, no distinct visible crystals without magnification, 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 5-6 on the Mohs scale, typically dark gray to black in color, aphanitic (fine-grained) texture, dull to submetallic luster, no distinct visible crystals without magnification, specific gravity around 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in iron and magnesium exposed at or very near the Earth's surface, often from volcanic eruptions or oceanic crust formation.
Uses & applications
Used extensively in construction (as crushed stone for roads, railroad ballast, and concrete aggregate), production of rock wool insulation, and occasionally as dimension stone.
Geological facts
Basalt is the most common rock type in the Earth's crust, particularly making up most of the ocean floor and large extraterrestrial volcanic provinces such as on the Moon and Mars.
Field identification & locations
Identify in the field by its dark gray to black color, heavy weight, fine-grained texture, and sometimes vesicular (gas bubble) cavities. Common worldwide in volcanic regions.
