igneous
Scoria (Vesicular Basalt)
Extrusive mafic igneous rock (high vesicularity)
Dark reddish-brown to dark gray or black color. Highly porous and full of vesicles (gas pockets). Hardness ranges from 5 to 6 on the Mohs scale. Luster is dull to earthy. Fine-grained or aphanitic matrix consisting mainly of plagioclase feldspar, pyroxene, and olivine.
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Physical properties
Dark reddish-brown to dark gray or black color. Highly porous and full of vesicles (gas pockets). Hardness ranges from 5 to 6 on the Mohs scale. Luster is dull to earthy. Fine-grained or aphanitic matrix consisting mainly of plagioclase feldspar, pyroxene, and olivine.
Formation & geological history
Formed during explosive volcanic eruptions when gas-rich mafic magma is ejected into the air. As the molten rock cools rapidly while airborne, trapped gas bubbles expand and freeze in place, leaving behind a porous, sponge-like vesicular texture.
Uses & applications
Widely used in landscaping as lava rock, in high-temperature insulation, as lightweight aggregate in concrete, in gas grill heat distribution, and as an abrasive material.
Geological facts
Unlike pumice, scoria is denser due to its higher iron and magnesium content, meaning it usually sinks in water rather than floating.
Field identification & locations
Easily identified by its dark reddish or black color combined with a highly pitted, porous, vesicular surface. Commonly found near active or extinct volcanic vents, cinder cones, and basaltic lava fields.
