igneous
Basalt
Aphanitic Mafic Igneous Rock
Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Microcrystalline (aphanitic); Cleavage: None; Specific gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Microcrystalline (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. Usually associated with volcanic activity and oceanic crust formation.
Uses & applications
Extensively used in construction for aggregate, road base, concrete, and railroad ballast. Also used as dimension stone and in high-temperature insulation (stone wool).
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identified in the field by its heavy weight, dark color, and fine-grained texture. It often shows weathering rinds of orange or brown. Commonly found in volcanic regions and river beds near basaltic flows.
