igneous
Porous vesicular volcanic rock (likely scoria)
Scoria; chiefly iron-rich volcanic glass with plagioclase, pyroxene, and/or olivine
AI-generated identification · may be incorrectHardness about 5–6 Mohs; rusty brown to dark gray, dull to slightly glassy luster, abundant rounded vesicles, and no obvious cleavage. Low-to-moderate density, though this specimen appears relatively compact and water-worn.
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Physical properties
Hardness about 5–6 Mohs; rusty brown to dark gray, dull to slightly glassy luster, abundant rounded vesicles, and no obvious cleavage. Low-to-moderate density, though this specimen appears relatively compact and water-worn.
Formation & geological history
Forms when gas-rich basaltic lava rapidly cools, trapping bubbles; commonly Quaternary to modern in age near cinder cones and lava flows. Its rounded shape and smoothed cavities suggest stream, beach, or other abrasion after formation.
Uses & applications
Used as lightweight aggregate, drainage and landscaping stone, abrasive, and decorative material; attractive pieces are collected but are generally not jewelry-grade.
Geological facts
Scoria differs from pumice by being darker, denser, and usually less frothy. The brown coloration commonly results from oxidation of iron-bearing minerals and volcanic glass.
Field identification & locations
Identify it by its dark rusty color, vesicles, irregular texture, and volcanic appearance; it is common in basaltic volcanic regions such as Hawaii, Iceland, the western United States, and the Mediterranean. A streak, density, and lack of carbonate reaction help distinguish it from porous sedimentary rock.
