igneous
Vesicular Basalt (Scoria)
Aphanitic Mafic Igneous Rock (Vesicular Basalt)
Hardness: 6.0; Color: Dark grey to reddish-black; Luster: Dull/Earthy; Structure: Vesicular (gas bubbles); Cleavage: None (conchoidal fracture); Specific Gravity: 2.8–3.0
- Hardness
- 6
- Color
- Dark grey to reddish-black
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6.0; Color: Dark grey to reddish-black; Luster: Dull/Earthy; Structure: Vesicular (gas bubbles); Cleavage: None (conchoidal fracture); Specific Gravity: 2.8–3.0
Formation & geological history
Formed during explosive volcanic eruptions or on the surface of lava flows when volcanic gases expand and get trapped in cooling magma during the Cenozoic era.
Uses & applications
Used in landscaping, lightweight concrete, gas grill lava rocks, drainage systems, and as an abrasive in stone-washing textiles.
Geological facts
The holes, called vesicles, are formed by gases coming out of solution as the magma depressurizes. If a specimen has enough holes, it can occasionally float on water briefly, though less so than pumice.
Field identification & locations
Identified by its swiss-cheese appearance and high density compared to pumice. Commonly found in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.
