igneous
Basalt
Basalt (Mafic Extrusive)
Hardness: 6.0 on Mohs scale. Color: Dark grey to black, sometimes greenish. Luster: Dull to sub-metallic when fresh. Crystal structure: Aphanitic (fine-grained), often containing phenocrysts of olivine or pyroxene. Specific gravity: 2.8–3.0.
- Hardness
- 6
- Color
- Dark grey to black, sometimes greenish
- Luster
- Dull to sub-metallic when fresh
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: 6.0 on Mohs scale. Color: Dark grey to black, sometimes greenish. Luster: Dull to sub-metallic when fresh. Crystal structure: Aphanitic (fine-grained), often containing phenocrysts of olivine or pyroxene. Specific gravity: 2.8–3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (magma) at or very near the Earth's surface. It is the most common rock type in Earth's crust, primarily making up the ocean floors.
Uses & applications
Extensively used in construction as aggregate for roads, railroad ballast, and concrete. It is also used as a dimension stone for flooring, monuments, and occasionally in stone wool insulation manufacturing.
Geological facts
Basalt is not only the most common rock on Earth but also on other terrestrial planets like Mars and Venus, and the Moon. The 'Maria' (dark plains) of the Moon are composed of basaltic lava flows.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often weathers to a reddish-brown color due to iron oxidation. Look for columnar jointing in large outcrops.
