igneous
Vesicular basalt (possibly scoriaceous basalt)
Basalt; chiefly plagioclase, clinopyroxene, and iron-rich minerals, with vesicles formerly filled by volcanic gas
AI-generated identification · may be incorrectDark gray-black, fine-grained, locally glassy and highly vesicular, with dull to submetallic luster; Mohs hardness about 5–6, no obvious cleavage, and typical specific gravity around 2.7–3.0 (lower if very porous).
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Physical properties
Dark gray-black, fine-grained, locally glassy and highly vesicular, with dull to submetallic luster; Mohs hardness about 5–6, no obvious cleavage, and typical specific gravity around 2.7–3.0 (lower if very porous).
Formation & geological history
An extrusive volcanic rock formed when mafic lava cooled rapidly at or near Earth’s surface, commonly during eruptions ranging from recent to Precambrian age; rusty areas represent oxidation or weathered secondary minerals.
Uses & applications
Used as aggregate, ballast, riprap, and occasionally decorative stone; porous scoria is also used in landscaping and lightweight concrete. This specimen has modest collector value unless its locality or vesicle mineralization is documented.
Geological facts
The holes are vesicles, created by expanding bubbles in lava; larger irregular cavities may be amygdules later lined or partly filled by zeolite, calcite, or quartz minerals.
Field identification & locations
Identify it by its black mafic color, very fine texture, abundant rounded cavities, and low-to-moderate density; a streak is usually gray-black and it is generally nonmagnetic to weakly magnetic. Common worldwide near basaltic volcanoes, including Hawaii, Iceland, Mexico, and oceanic islands.
