igneous
Basalt (Vesicular or Scoriaceous)
Aphanitic Mafic Volcanic Rock
Hardness: 5-6 Mohs. Color: dark grey to black. Luster: dull to slightly vitreous. Structure: fine-grained (aphanitic) with small vesicles. Specific gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- dark grey to black
- Luster
- dull to slightly vitreous
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Physical properties
Hardness: 5-6 Mohs. Color: dark grey to black. Luster: dull to slightly vitreous. Structure: fine-grained (aphanitic) with small vesicles. Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. The small holes (vesicles) are created by trapped gas bubbles escaping as the lava solidifies.
Uses & applications
Used extensively in construction as aggregate for concrete and asphalt, as road base, and for railroad ballast. High-quality specimens are used in stone masonry and landscaping.
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 compared to other light rocks, and fine-grained texture. Found near volcanic hotspots and oceanic ridges.
