igneous
Basalt (Road Aggregate Specimen)
Aphanitic mafic volcanic rock
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull; Crystal structure: Fine-grained/aphanitic; Specific gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black
- Luster
- Dull
Identified More igneous →
Explore Basalt (Road Aggregate Specimen) 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; Luster: Dull; 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 the Earth's surface. Basalt is common throughout Earth's history, spanning billions of years to modern volcanic eruptions.
Uses & applications
Crushed stone for road construction, concrete aggregate, railroad ballast, and high-strength industrial flooring.
Geological facts
Basalt is the most common rock type in Earth's crust and also makes up most of the surface of the moon and Mars.
Field identification & locations
Identified by its dense, dark, fine-grained texture and heavy weight. Commonly found near volcanic sites or as crushed aggregate in urban environments.
