igneous
Basalt
Aphanitic Mafic Volcanic Rock (Fe/Mg rich)
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull/Earthy; Crystal structure: Fine-grained/Aphanitic; Specific gravity: 2.8-3.0
- Hardness
- 6 (Mohs)
- Color
- Dark grey to black
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull/Earthy; 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 surface of the Earth.
Uses & applications
Extensively used in construction, especially as aggregate for asphalt and concrete, road base, and railroad ballast.
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 and Mars.
Field identification & locations
Identify by its dark color, heavy weight (density), and lack of visible crystals. Commonly found in volcanic fields, lava plateaus, and oceanic islands.
