igneous
Scoria (Volcanic Cinder)
Extrusive Igneous Rock
Hardness of 5-6 on the Mohs scale; color ranges from dark brown to reddish-brown; vesicular texture with abundant gas bubble cavities; dull luster; specific gravity typically less than 1.0 if it floats, though denser varieties exist.
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Physical properties
Hardness of 5-6 on the Mohs scale; color ranges from dark brown to reddish-brown; vesicular texture with abundant gas bubble cavities; dull luster; specific gravity typically less than 1.0 if it floats, though denser varieties exist.
Formation & geological history
Formed from gas-rich mafic to intermediate lava that erupted from a volcano. As the lava depressurizes and cools rapidly, escaping gases create bubbles trapped within the solidifying rock.
Uses & applications
Used in landscaping, lightweight aggregate in concrete, gas barbecue grills, and as a soil amendment (expanded clay/shale alternative).
Geological facts
Due to its high vesicularity, many varieties of scoria have a low enough density to float on water until water fills the air pockets.
Field identification & locations
Easily identified by its reddish or dark brown color, rough, vesicular surface, and lightweight feel. Commonly found around volcanic cinder cones worldwide.
