igneous
Vesicular Basalt
Vesicular Basalt (Aphanitic-Vesicular Mafic Rock)
Hardness: 6 (Mohs); Color: dark brown to black (mafic); Luster: dull to earthy; Structure: vesicular (pitted with gas bubbles); Specific Gravity: 2.8-3.0
- Hardness
- 6 (Mohs)
- Color
- dark brown to black (mafic)
- Luster
- dull to earthy
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Physical properties
Hardness: 6 (Mohs); Color: dark brown to black (mafic); Luster: dull to earthy; Structure: vesicular (pitted with gas bubbles); 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, where escaping gases leave behind bubble-like cavities (vesicles).
Uses & applications
Used primarily in construction for lightweight aggregate, railway ballast, and sometimes in landscaping or for decorative stone aquarium filters.
Geological facts
Vesicles represent gas bubbles trapped as the lava solidified; if the holes later fill with minerals, the rock is called amygdaloidal basalt.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and characteristic 'swiss cheese' texture. Commonly found in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.
