igneous
Scoria (vesicular basalt)
Vesicular basalt; chiefly plagioclase, pyroxene, and iron-rich volcanic glass
AI-generated identification · may be incorrectDark reddish-brown, highly vesicular, rough, and typically dull to slightly glassy; Mohs hardness about 5–6, no cleavage, fine-grained groundmass, and relatively low-to-moderate specific gravity (about 2.0–2.7). The blue-green patches may be secondary mineral coatings or weathering products.
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Physical properties
Dark reddish-brown, highly vesicular, rough, and typically dull to slightly glassy; Mohs hardness about 5–6, no cleavage, fine-grained groundmass, and relatively low-to-moderate specific gravity (about 2.0–2.7). The blue-green patches may be secondary mineral coatings or weathering products.
Formation & geological history
Forms when gas-rich basaltic lava erupts and rapidly cools, trapping bubbles; oxidation of iron produces the red-brown color. It is generally Quaternary to Cenozoic, though scoria occurs in volcanic rocks of many ages.
Uses & applications
Used as lightweight aggregate, drainage material, landscaping stone, abrasives, and occasionally in decorative or lapidary pieces.
Geological facts
Scoria is denser and commonly darker than pumice, whose abundant interconnected pores allow it to float. Vesicles are gas bubbles preserved in the lava.
Field identification & locations
Identify it by its black-to-red color, abundant irregular holes, rough texture, and volcanic appearance; common around cinder cones and basaltic lava fields worldwide, including Iceland, Mexico, Italy, and the western United States.
