igneous
Vesicular Basalt (Scoria)
Aphanitic Mafic Igneous Rock (primarily Plagioclase and Pyroxene)
Hardness: 5-6 (Mohs); Color: Dark brown, reddish-brown, to black; Luster: Dull/Earthy; Crystal Structure: Microcrystalline (aphanitic); Features: Highly vesicular/pitted texture with air bubbles (vesicles), specific gravity of 2.5-3.0.
- Hardness
- 5-6 (Mohs)
- Color
- Dark brown, reddish-brown, to black
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark brown, reddish-brown, to black; Luster: Dull/Earthy; Crystal Structure: Microcrystalline (aphanitic); Features: Highly vesicular/pitted texture with air bubbles (vesicles), specific gravity of 2.5-3.0.
Formation & geological history
Formed during explosive volcanic eruptions where dissolved gases expand rapidly as magma reaches the surface, cooling quickly to trap bubbles in the solidifying rock. Common in Cenozoic volcanic fields.
Uses & applications
Used in landscaping as volcanic rock, high-temperature insulation, drainage rock, and as an additive in lightweight concrete. Large pieces are valued by aquarium hobbyists.
Geological facts
Because it is so full of air bubbles, scoria is significantly lighter than solid basalt. Similar rocks with even higher gas content that can float on water are known as pumice.
Field identification & locations
Identified in the field by its dark color, rough/scratchy texture, and visible pits or holes. Found globally in volcanic regions like Hawaii, Iceland, and the western United States.
