igneous
Basalt
Extrusive mafic igneous rock
Hardness: 6 on Mohs scale; Color: black to dark gray; Luster: dull to earthy; Crystal structure: aphanitic (fine-grained); Cleavage: none; Specific gravity: 2.8-3.0.
- Hardness
- 6 on Mohs scale
- Color
- black to dark gray
- Luster
- dull to earthy
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: 6 on Mohs scale; Color: black to dark gray; Luster: dull to earthy; Crystal structure: aphanitic (fine-grained); Cleavage: none; Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. Most of the Earth's oceanic crust is composed of basalt.
Uses & applications
Used primarily in construction (crushed stone for road base, railroad ballast, and concrete aggregate), as well as in the manufacturing of stone wool insulation and occasionally for decorative landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust and also covers large areas of the Moon, Mars, and Venus. The Giant's Causeway in Northern Ireland is a famous example of columnar basalt joints.
Field identification & locations
Identify by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. Often found in volcanic regions, oceanic islands, and mid-ocean ridges.
