igneous
Scoria (Lava Rock)
Scoria (highly vesicular extrusive igneous rock)
Hardness: 5-6 (Mohs scale), Color: Dark red to reddish-brown (oxidized iron), Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Cleavage: None, Specific Gravity: 2.5-3.0 (though it often feels lighter due to air pockets)
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Physical properties
Hardness: 5-6 (Mohs scale), Color: Dark red to reddish-brown (oxidized iron), Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Cleavage: None, Specific Gravity: 2.5-3.0 (though it often feels lighter due to air pockets)
Formation & geological history
Formed from the rapid cooling of gas-rich basaltic or andesitic lava. As the lava is ejected during a volcanic eruption, gas bubbles (vesicles) are trapped as the rock solidifies. Most specimens are relatively young geologically (Cenozoic era).
Uses & applications
Commonly used in landscaping and garden mulch for its decorative color and water retention. Used in high-temperature insulation, gas grills (lava rocks), lightweight concrete, and road traction on snowy surfaces.
Geological facts
Unlike pumice, which is also vesicular, scoria typically has larger holes, thicker walls, and is dense enough to sink in water. Its red color is usually due to the oxidation of iron within the lava as it reacts with the atmosphere.
Field identification & locations
Identify by its highly porous, honeycomb-like texture and rough, abrasive surface. It is very light for its size but usually does not float. Commonly found in volcanic fields such as those in Iceland, Hawaii, the Canary Islands, and the western United States.
