igneous
Vesicular Basalt
Vesicular Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 5-6 (Mohs); Color: Dark gray, reddish-brown, or black; Luster: Dull/Earthy; Crystal Structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.8-3.0; Texture: Vesicular (pitted with gas bubbles).
- Hardness
- 5-6 (Mohs)
- Color
- Dark gray, reddish-brown, or black
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark gray, reddish-brown, or black; Luster: Dull/Earthy; Crystal Structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.8-3.0; Texture: Vesicular (pitted with gas bubbles).
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (basaltic) expelled from a volcano. The small holes, or vesicles, formed as gas bubbles were trapped as the lava solidified. They are found in volcanic regions spanning from the Precambrian to present day.
Uses & applications
Used fundamentally in construction as aggregate for roads and railways, in high-strength concrete, and often in landscaping as decorative 'lava rock'.
Geological facts
Basalt is the most common rock type in Earth's crust and makes up most of the ocean floor. Vesicular basalt that is extremely porous is known as scoria.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and distinct 'Swiss cheese' texture. Commonly found in volcanic fields, ocean ridges, and basaltic plateaus like the Deccan Traps or Columbia River Plateau.
