igneous
Scoria
Scoria (vesicular basalt-andesite)
Hardness: 5-6 (Mohs); Color: Dark reddish-brown to black; Luster: Dull, earthy; Structure: Highly vesicular (pitted with gas bubbles); Cleavage: None; Specific gravity: Low (often sinks in water, unlike pumice)
- Hardness
- 5-6 (Mohs)
- Color
- Dark reddish-brown to black
- Luster
- Dull, earthy
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark reddish-brown to black; Luster: Dull, earthy; Structure: Highly vesicular (pitted with gas bubbles); Cleavage: None; Specific gravity: Low (often sinks in water, unlike pumice)
Formation & geological history
Formed from the rapid cooling of gas-rich mafic lava during explosive volcanic eruptions. The vesicles are formed by trapped gas bubbles that expand as pressure drops during the eruption. Found in cinder cones and volcanic fields.
Uses & applications
Used in landscaping as decorative ground cover, high-temperature insulation, drainage rock, and in lightweight concrete as an aggregate.
Geological facts
Scoria is a common component of cinder cones, which are the smallest and most common type of volcano. Unlike pumice, scoria has larger vesicles and thicker cell walls, making it dense enough to sink in water.
Field identification & locations
Identify by its characteristic 'sponge-like' appearance with many holes, its rough/abrasive texture, and it is usually darker and heavier than pumice. Common in volcanic regions like the American Southwest, Iceland, and Italy.
