igneous
Vesicular Basalt (Scoria)
Vesicular Basalt
Hardness: 5-6 Mohs. Color: Dark gray, black, or reddish-brown with green olivine inclusions. Luster: Dull to earthy. Structure: Vesicular (pitted with gas bubbles). Cleavage: None. Specific gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Luster
- Dull to earthy
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Physical properties
Hardness: 5-6 Mohs. Color: Dark gray, black, or reddish-brown with green olivine inclusions. Luster: Dull to earthy. Structure: Vesicular (pitted with gas bubbles). Cleavage: None. Specific gravity: 2.8-3.0.
Formation & geological history
Formed from rapid cooling of mafic lava rich in dissolved gases. As the lava depressurizes upon erupting, gas bubbles (vesicles) are trapped as the rock solidifies. Common in volcanic fields of various geological ages.
Uses & applications
Used in landscaping, high-temperature insulation, gas grill stones, drainage systems, and as an abrasive in stone-washing processes. Small specimens are collected for educational purposes.
Geological facts
The holes in this rock, called vesicles, are actually prehistoric gas bubbles. If the bubbles are large and numerous enough, the rock can become lightweight, though unlike pumice, basaltic scoria usually sinks in water.
Field identification & locations
Identify by its dark color, heavy weight compared to pumice, and the presence of small circular cavities. Often found near cinder cones or basaltic lava flows. Green tints usually indicate the presence of olivine.
