igneous
Vesicular Basalt
Extrusive Mafic Igneous Rock (Vesicular Basalt)
Hardness: 5-6 Mohs. Color: dark grey to black. Luster: dull to sub-metallic. Crystal structure: fine-grained (aphanitic). Features: prominent vesicles (gas bubbles). Specific Gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- dark grey to black
- Luster
- dull to sub-metallic
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Physical properties
Hardness: 5-6 Mohs. Color: dark grey to black. Luster: dull to sub-metallic. Crystal structure: fine-grained (aphanitic). Features: prominent vesicles (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. The holes or 'vesicles' are formed by gas bubbles that were trapped in the lava as it solidified.
Uses & applications
Used in landscaping, as an abrasive in 'stone-washed' fabric processing, in construction as aggregate, and sometimes in sauna heaters due to heat retention.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Large-scale basaltic flows can form unique hexagonal columns, such as at the Giant's Causeway.
Field identification & locations
Look for a heavy, dark-colored rock with many small holes or pits. Commonly found in volcanic regions such as Hawaii, Iceland, or the Pacific Northwest. Not to be confused with pumice, which is much lighter and can float.
