igneous
Basalt
Aphanitic Mafic Igneous Rock
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Fine-grained (aphanitic); Cleavage: None; Specific gravity: 2.8 - 3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Fine-grained (aphanitic); Cleavage: None; Specific gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. It is the most common volcanic rock on Earth.
Uses & applications
Extensively used in construction, specifically for aggregate in road base, concrete, and railroad ballast. It is also used as a dimension stone for flooring and landscaping.
Geological facts
Basalt is equivalent to the composition of Earth's oceanic crust. It is also found on the Moon and Mars, where basaltic plains (marias) cover vast areas.
Field identification & locations
Identified in the field by its dark color, heavy weight (relative to size), and lack of visible crystals. It is found globally in volcanic regions like Hawaii, Iceland, and the Columbia River Plateau.
