igneous
Scoria
Extrusive igneous basaltic rock
Hardness: 5-6 (Mohs scale); Color: Dark reddish-brown to dark gray/black; Luster: Dull to earthy; Texture: Vesicular (porous, filled with small cavities/vesicles); Density: Low density due to air pockets, though denser than pumice
- Hardness
- 5-6 (Mohs scale)
- Color
- Dark reddish-brown to dark gray/black
- Luster
- Dull to earthy
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark reddish-brown to dark gray/black; Luster: Dull to earthy; Texture: Vesicular (porous, filled with small cavities/vesicles); Density: Low density due to air pockets, though denser than pumice
Formation & geological history
Formed during explosive volcanic eruptions when gas-rich basaltic or andesitic lava is ejected into the air. As the lava cools rapidly, trapped gas bubbles form small vesicles before the rock solidifies.
Uses & applications
Used in landscaping, high-temperature insulation, barbecue gas grills as heat retainers, lightweight concrete aggregate, and decorative stone work.
Geological facts
Scoria differs from pumice because it has thicker cell walls and higher density, causing scoria to sink in water whereas pumice floats. The reddish color often comes from the oxidation of iron in the lava during eruption.
Field identification & locations
Identified in the field by its dark red to black color, rough surface, and abundant small holes (vesicles). Commonly found in volcanic fields, cinder cones, and lava flow areas around active or extinct volcanoes worldwide.
