igneous
Basalt
Mafic volcanic rock
Hardness (Mohs scale): 6; Color: Dark grey to black; Luster: Dull or sub-metallic; Crystal structure: Fine-grained/aphanitic; Specific gravity: 2.8 - 3.0
- Color
- Dark grey to black
- Luster
- Dull or sub-metallic
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness (Mohs scale): 6; Color: Dark grey to black; Luster: Dull or sub-metallic; Crystal structure: Fine-grained/aphanitic; 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 specimen appears water-worn, suggesting it was shaped by river or coastal erosion.
Uses & applications
Commonly used in construction for road base, concrete aggregate, and railroad ballast. It is also used as dimension stone for tiles and memorials.
Geological facts
Basalt is the most common rock on Earth's surface and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify in the field by its high density, dark color, and lack of visible crystals. It is ubiquitous in volcanic regions and along contemporary or ancient riverbeds.
