igneous
Scoria (Lava Rock)
Scoria
Hardness: 5.0 - 6.0; Color: Dark red to reddish-brown (due to iron oxidation); Luster: Dull to sub-vitreous; Structure: Vesicular (highly porous/holey); Specific Gravity: 0.8 - 2.1 (low, but usually sinks in water contrast to pumice).
- Hardness
- 5
- Color
- Dark red to reddish-brown (due to iron oxidation)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 5.0 - 6.0; Color: Dark red to reddish-brown (due to iron oxidation); Luster: Dull to sub-vitreous; Structure: Vesicular (highly porous/holey); Specific Gravity: 0.8 - 2.1 (low, but usually sinks in water contrast to pumice).
Formation & geological history
Formed from extrusive volcanic activity during explosive eruptions. Gasses trapped in cooling basaltic or andesitic magma create bubbles (vesicles) as the pressure drops suddenly upon surfacing.
Uses & applications
Commonly used in landscaping as decorative ground cover, in gas grills as 'lava rocks' for heat retention, in high-temperature insulation, and as lightweight aggregate for concrete.
Geological facts
Unlike its cousin pumice, scoria typically has larger holes and thicker walls, making it dense enough to sink in water. The red color is usually a result of the oxidation of iron within the lava while it is still hot.
Field identification & locations
Identify in the field by its sponge-like, porous appearance and relatively light weight despite being rock. Found near cinder cones and volcanic vents worldwide, particularly in Hawaii, Iceland, and the Canary Islands.
