igneous
Vesicular Basalt (Scoria)
Scoriaceous Basalt (FeMgSiO3-rich)
Hardness: 5-6 (Mohs); Color: Dark brown, black, or reddish-brown; Luster: Dull/Sub-metallic; Structure: Highly vesicular (honeycombed with gas bubbles); Cleavage: None; Specific Gravity: 2.5-3.0.
- Hardness
- 5-6 (Mohs)
- Color
- Dark brown, black, or reddish-brown
- Luster
- Dull/Sub-metallic
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark brown, black, or reddish-brown; Luster: Dull/Sub-metallic; Structure: Highly vesicular (honeycombed with gas bubbles); Cleavage: None; Specific Gravity: 2.5-3.0.
Formation & geological history
Formed through the rapid cooling of mafic lava containing high amounts of dissolved gases. As the lava erupts, the gases expand and escape, leaving behind a porous, vesicular texture. Most specimens range from Cenozoic to recent geological ages.
Uses & applications
Used primarily in landscaping, gas grill lava rocks, drainage systems, and as an abrasive in 'stone-washed' textile production.
Geological facts
Scoria is similar to pumice, but because it is basaltic, it has larger vesicles and thicker cell walls, making it dense enough to sink in water, unlike most pumice.
Field identification & locations
Identify in the field by its dark color, lightweight feel compared to solid rock, and the presence of numerous circular or elliptical pits (vesicles). Commonly found in volcanic fields such as those in the Western US, Italy, or Iceland.
