igneous
Scoria
Scoriaceous Basalt
Hardness: 5-6 Mohs; Color: reddish-brown to dark gray/black; Luster: dull/sub-metallic; Crystal structure: fine-grained (aphanitic) with vesicular texture; Specific gravity: approx. 0.8-2.1 (can be light but usually sinks in water, unlike pumice)
- Hardness
- 5-6 Mohs
- Color
- reddish-brown to dark gray/black
- Luster
- dull/sub-metallic
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Physical properties
Hardness: 5-6 Mohs; Color: reddish-brown to dark gray/black; Luster: dull/sub-metallic; Crystal structure: fine-grained (aphanitic) with vesicular texture; Specific gravity: approx. 0.8-2.1 (can be light but usually sinks in water, unlike pumice)
Formation & geological history
Formed from basaltic or andesitic magma containing dissolved gases. As the magma erupts, gases expand to form bubbles (vesicles) that are frozen in place as the lava cools rapidly. Often found on the flanks of cinder cone volcanoes.
Uses & applications
Commonly used in landscaping as decorative 'lava rock', in high-temperature gas grills, for drainage control in construction, and as lightweight aggregate in concrete and sauna rocks.
Geological facts
Scoria is technically a glass, but its many cavities make it look like a stony sponge. Unlike pumice, which is also vesicular, scoria is typically darker and heavier because it contains more iron and magnesium.
Field identification & locations
Identify by its characteristic 'swiss cheese' holes (vesicles) and relatively light weight compared to solid basalt. It is usually rough to the touch. Commonly found in volcanic regions like Hawaii, the American Southwest, or Iceland.
