igneous
Basalt
Basalt (extrusive volcanic rock)
Hardness: 6 (Mohs scale); Color: Dark gray to black, often weathering to brownish or greenish; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained), often containing phenocrysts of olivine or pyroxene; Specific gravity: 2.8–3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black, often weathering to brownish or greenish
- Luster
- Dull to sub-metallic
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 (Mohs scale); Color: Dark gray to black, often weathering to brownish or greenish; Luster: Dull to sub-metallic; 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 exposed at or very near the surface of a terrestrial planet or a moon. It is the most common volcanic rock on Earth, making up most of the ocean floor.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and floor tiles. It is also used in the manufacturing of stone wool insulation.
Geological facts
Basalt is found on the Moon, Mars, and Venus. The Giant's Causeway in Northern Ireland and the columnar joints of Devil's Postpile in California are famous basaltic formations.
Field identification & locations
Identify in the field by its dark color, fine grain size, and heavy weight (density). It is commonly found in volcanic regions, oceanic crust, and riverbeds where it has been smoothed by water into 'river rocks.'
