igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6.0; Color: Dark grey to black or olive green; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
- Hardness
- 6
- Color
- Dark grey to black or olive green
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6.0; Color: Dark grey to black or olive green; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); 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
Extensively used in construction as crushed stone for road base, concrete aggregate, and railroad ballast. Also used as a raw material for stone wool insulation.
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 and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and absence of visible crystals. Commonly found in lava flow fields and oceanic ridges.
