igneous
Scoria
Vesicular Basalt / Scoria
Hardness: 5-6 (Mohs scale); Color: Dark brown, black, or reddish; Luster: Dull (earthy); Crystal structure: Aphanitic (fine-grained) with large vesicles; Specific gravity: 2.5-3.0 (though it often feels lighter due to air pockets).
- Hardness
- 5-6 (Mohs scale)
- Color
- Dark brown, black, or reddish
- Luster
- Dull (earthy)
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark brown, black, or reddish; Luster: Dull (earthy); Crystal structure: Aphanitic (fine-grained) with large vesicles; Specific gravity: 2.5-3.0 (though it often feels lighter due to air pockets).
Formation & geological history
Formed from gas-rich basaltic magma cooling rapidly during a volcanic eruption. As the pressure drops, dissolved gases expand into bubbles which are trapped as the lava solidifies, creating a 'vesicular' texture.
Uses & applications
Used in high-temperature insulation, lightweight concrete, landscaping (lava rock), drainage stone, and as an abrasive in 'stone-washed' jeans.
Geological facts
Scoria is different from pumice in that it has larger vesicles and thicker cell walls, making it dense enough to sink in water, whereas pumice often floats.
Field identification & locations
Identify by its dark color, high porosity with visible rounded holes, and relatively heavy feel compared to pumice. Common in volcanic fields like those in Iceland, Hawaii, and the Western US.
