igneous
Scoria (vesicular basalt)
Scoria; mafic volcanic rock composed mainly of plagioclase, pyroxene, olivine, and volcanic glass
AI-generated identification · may be incorrectHardness about 5–6 Mohs; reddish-brown to black, dull to mildly vitreous, highly vesicular, with fine crystalline to glassy texture and no prominent cleavage. Its low density results from abundant gas cavities, though this specimen appears relatively compact.
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Physical properties
Hardness about 5–6 Mohs; reddish-brown to black, dull to mildly vitreous, highly vesicular, with fine crystalline to glassy texture and no prominent cleavage. Its low density results from abundant gas cavities, though this specimen appears relatively compact.
Formation & geological history
Forms when gas-rich basaltic lava froths and rapidly cools during volcanic eruptions, commonly in cinder cones and lava flows. Most examples are geologically young, ranging from Holocene to Cenozoic, although older scoria also occurs.
Uses & applications
Used as lightweight aggregate, drainage and landscaping stone, abrasive, and soil amendment; attractive pieces are collected but rarely used in jewelry.
Geological facts
The red color commonly develops through oxidation of iron minerals during or after eruption. Scoria differs from pumice because it is darker, denser, and formed from iron- and magnesium-rich magma.
Field identification & locations
Identify it by its dark red/black color, numerous irregular vesicles, lightweight feel, and rough surface; it is common near basaltic volcanoes worldwide, including Hawaii, Iceland, Italy, and the western United States.
