igneous
Vesicular Basalt
Extrusive Mafic Igneous Rock with Vesicular Texture
Hardness: 5-6 (Mohs); Color: Dark gray to light gray/blue (weathered); Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Porosity: High due to vesicles (gas bubbles); Specific Gravity: 2.8-3.0.
- Hardness
- 5-6 (Mohs)
- Color
- Dark gray to light gray/blue (weathered)
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark gray to light gray/blue (weathered); Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Porosity: High due to vesicles (gas bubbles); Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (basaltic) erupted at the Earth's surface or on the ocean floor. The holes (vesicles) are formed by trapped gas bubbles escaping as the lava solidifies. Typically found in volcanic fields or as beach cobbles eroded from volcanic cliffs.
Uses & applications
Used in landscaping, construction (as aggregate), road stone, and heat-retention stones for saunas or massages. Large weathered pieces are often kept as decorative garden specimens.
Geological facts
This specimen shows significant rounding, suggesting it has been tumbled in a high-energy aquatic environment like a beach or river for a long period. Some of the vesicles appear to have secondary mineral infilling starting to occur, which could eventually lead to amygdaloidal basalt.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to pumice), and the presence of small circular pits or holes. It is widespread in volcanic regions like Iceland, Hawaii, and parts of the Pacific Northwest.
