igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 on Mohs scale; Color: Black to dark gray; Luster: Dull to sub-metallic; Structure: Fine-grained aphanitic; Cleavage: None; Specific Gravity: 2.8–3.0
- Hardness
- 6 on Mohs scale
- Color
- Black to dark gray
- 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 on Mohs scale; Color: Black to dark gray; Luster: Dull to sub-metallic; Structure: Fine-grained aphanitic; Cleavage: None; Specific Gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This particular specimen shows river-worn softening and possible quartz veining.
Uses & applications
Primarily used in construction as aggregate for roads and concrete, high-quality slabs for architecture, and occasionally for ground-line carvings.
Geological facts
Basalt is the most common rock type in Earth's crust and also makes up most of the surface of the Moon (the Lunar Maria).
Field identification & locations
Identify by its dark color, heavy weight for its size, and absence of visible large crystals. Commonly found in volcanic regions or as rounded cobbles in riverbeds.
