igneous
Basalt
Basalt (Volcanic Mafic Rock)
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull/Submetallic; Crystal structure: Aphanitic (fine-grained crystals); Cleavage: None; Specific Gravity: 2.8-3.0.
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull/Submetallic
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull/Submetallic; Crystal structure: Aphanitic (fine-grained crystals); 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. Common in oceanic crust and volcanic islands.
Uses & applications
Used extensively in construction as road base, concrete aggregate, railroad ballast, and for architectural stone or statues.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the surface of the Moon (the lunar maria).
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture that lacks visible crystals to the naked eye. Commonly found in old volcanic regions and coastal areas.
