igneous
Basalt Scoria
Scoria (vesicular basalt)
Hardness: 5-6 (Mohs); Color: Dark brown, black, or reddish-brown; Luster: Dull/earthy; Structure: Highly vesicular (pitted with gas bubbles); Specific Gravity: 2.5-3.0 (though it feels light due to holes).
- Hardness
- 5-6 (Mohs)
- Color
- Dark brown, black, or reddish-brown
- Luster
- Dull/earthy
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark brown, black, or reddish-brown; Luster: Dull/earthy; Structure: Highly vesicular (pitted with gas bubbles); Specific Gravity: 2.5-3.0 (though it feels light due to holes).
Formation & geological history
Formed during explosive volcanic eruptions when magma containing dissolved gases is ejected into the air; the cooling rock solidifies around gas bubbles creating a vesicular texture. Usually of Cenozoic age in surface occurrences.
Uses & applications
Used in landscaping as lava rock, for drainage in gardening, as an abrasive in stone-washing jeans, and as a lightweight aggregate in concrete and heat-insulating building materials.
Geological facts
Unlike pumice, scoria has larger bubbles and thicker cell walls, causing most specimens to sink in water rather than float. It is a common constituent of cinder cones.
Field identification & locations
Identified by its dark color and 'Swiss cheese' appearance with many holes (vesicles). To distinguish from pumice, look for dark color and a density that usually feels heavier than pumice but lighter than solid basalt.
