igneous
Scoria (Lava Rock)
Scoria (Vesicular Basalt)
Hardness: 5-6 Mohs; Color: reddish-brown, dark red, or black; Luster: dull/earthy; Crystal Structure: aphanitic (fine-grained) with large vesicles; Specific Gravity: 2.5-3.0 (but low bulk density due to air pockets)
- Hardness
- 5-6 Mohs
- Color
- reddish-brown, dark red, or black
- Luster
- dull/earthy
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Physical properties
Hardness: 5-6 Mohs; Color: reddish-brown, dark red, or black; Luster: dull/earthy; Crystal Structure: aphanitic (fine-grained) with large vesicles; Specific Gravity: 2.5-3.0 (but low bulk density due to air pockets)
Formation & geological history
Formed from the cooling of mafic lava (high in iron and magnesium) that contains high amounts of dissolved gases. As the lava is ejected during volcanic activity, gas bubbles expand and become trapped as the rock solidifies, creating a vesicular texture.
Uses & applications
Commonly used in landscaping (lava rocks), as a lightweight aggregate in concrete, for high-temperature insulation, and in sauna heaters. It is also used in traction control on icy roads.
Geological facts
Unlike pumice, which is also a volcanic rock with holes, scoria has larger vesicles and thicker cell walls, which causes it to sink in water whereas pumice usually floats.
Field identification & locations
Identify in the field by its distinctive 'swiss cheese' or honeycomb texture and relatively low weight compared to solid basalt. Often found in volcanic cinder cones in places like the American Southwest, Iceland, and Italy.
