igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
AI-generated identification · may be incorrectHardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Sub-metallic; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull/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 grey to black; Luster: Dull/Sub-metallic; Crystal Structure: Aphanitic (fine-grained); 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 moon. Most basalt flows on Earth have occurred within the last 200 million years.
Uses & applications
Used widely in construction as highway aggregate, railroad ballast, and in concrete. Polished basalt is used for tiles, countertops, and decorative landscape stones.
Geological facts
Basalt is the most common rock on Earth's surface, making up most of the ocean floor. Large areas of the Moon's surface are covered in basaltic lava flows called 'maria.'
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often breaks into angular fragments. It is ubiquitous along coastlines and volcanic regions.
