igneous
Scoria
Vesicular Basalt / Scoriaceous Basalt
Hardness: 5-6 (Mohs scale); Color: Dark red, black, or reddish-brown; Luster: Dull (sub-vitreous); Crystal Structure: Aphanitic (fine-grained) with high vesicularity; Specific Gravity: 0.8-2.1 (relatively lightweight due to gas bubbles).
- Hardness
- 5-6 (Mohs scale)
- Color
- Dark red, black, or reddish-brown
- Luster
- Dull (sub-vitreous)
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark red, black, or reddish-brown; Luster: Dull (sub-vitreous); Crystal Structure: Aphanitic (fine-grained) with high vesicularity; Specific Gravity: 0.8-2.1 (relatively lightweight due to gas bubbles).
Formation & geological history
Formed through the rapid cooling of basaltic or andesitic lava containing high concentrations of trapped gases. As the lava erupts, the pressure drops, gas bubbles expand, and the rock solidifies while the bubbles are still present. Typically associated with volcanic cinder cones and quaternary geological ages.
Uses & applications
Used widely in landscaping (lava rocks), as high-temperature insulation, in the production of lightweight concrete, and as high-traction base material for roads in icy conditions.
Geological facts
Scoria is often mistaken for pumice; however, scoria is denser, has larger vesicles, and is typically basaltic (dark) rather than rhyolitic (light). It is the primary component of many iconic volcanic cinder cones found around the world.
Field identification & locations
Identify in the field by its dark reddish-black color and 'Swiss cheese' texture. Found in volcanic regions like the American Southwest, Iceland, and Hawaii. Collectors look for pieces with unique flow patterns or iridescent surfaces.
