igneous
Scoria (vesicular basalt)
Scoria; iron- and magnesium-rich volcanic rock, chiefly plagioclase, pyroxene, and olivine
AI-generated identification · may be incorrectDark black to reddish-brown, highly vesicular, rough, and commonly glassy to dull; hardness about 5–6 Mohs, with no prominent cleavage and low-to-moderate specific gravity. The specimen’s porous texture and irregular volcanic shape are characteristic.
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Physical properties
Dark black to reddish-brown, highly vesicular, rough, and commonly glassy to dull; hardness about 5–6 Mohs, with no prominent cleavage and low-to-moderate specific gravity. The specimen’s porous texture and irregular volcanic shape are characteristic.
Formation & geological history
Forms when gas-rich basaltic magma erupts and rapidly cools, trapping bubbles; it is generally Quaternary to modern in age and occurs in cinder cones, lava flows, and volcanic fields.
Uses & applications
Used as lightweight aggregate, drainage material, landscaping rock, abrasive, and sometimes as a decorative stone; it has little jewelry value.
Geological facts
Scoria is denser and darker than pumice because basaltic magma contains more iron and magnesium. Its vesicles are frozen gas bubbles, not holes caused by weathering.
Field identification & locations
Identify it by its black or rust-red color, abundant angular vesicles, rough surface, and light weight compared with solid basalt; common around basaltic volcanoes worldwide. A small common specimen is typically worth $1–$10, while attractive large or locality-labeled pieces may sell for $15–$50.
