Igneous
Basalt
Mafic Igneous Rock (composed primarily of Pyroxene and Plagioclase Feldspar)
Hardness: 6 (Mohs scale); Color: Dark gray to black (often weathers to brown/green); Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained, invisible crystals); Specific gravity: 2.8 - 3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black (often weathers to brown/green)
- 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 weathers to brown/green); Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained, invisible crystals); Specific gravity: 2.8 - 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity magnesium and iron-rich lava at or very near the surface. It is the most common rock in Earth's crust, making up most of the ocean floors. Geological age varies from modern volcanic flows to billions of years old.
Uses & applications
Extensively used as an aggregate in construction projects (road base, concrete, railroad ballast). Finely crushed basalt is used in agriculture for soil remineralization and as a raw material for stone wool insulation.
Geological facts
Basalt is also found on other terrestrial planets like Mars and Venus, and makes up the vast 'Maria' (dark plains) of the Moon. It is the extrusive equivalent of the intrusive rock Gabbro.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture. It often shows 'vesicles' (gas bubble holes) or a conchoidal fracture. Commonly found in volcanic regions, oceanic islands (like Hawaii), and mid-ocean ridges.
