igneous
Vesicular basalt (likely weathered volcanic scoria)
Basalt; chiefly plagioclase feldspar, pyroxene, and minor olivine, with vesicles formed by trapped gas
AI-generated identification · may be incorrectTypically dark gray to brown, fine-grained, dull to slightly glassy, and commonly vesicular; Mohs hardness about 6, with no obvious cleavage and specific gravity roughly 2.7–3.0. This specimen appears heavily weathered and unusually pale, with small gas cavities and possible mineral-filled vesicles.
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Physical properties
Typically dark gray to brown, fine-grained, dull to slightly glassy, and commonly vesicular; Mohs hardness about 6, with no obvious cleavage and specific gravity roughly 2.7–3.0. This specimen appears heavily weathered and unusually pale, with small gas cavities and possible mineral-filled vesicles.
Formation & geological history
An extrusive igneous rock formed when low-silica lava cooled rapidly at or near Earth’s surface, commonly during Cenozoic or older volcanic eruptions. Weathering has oxidized and lightened its surface.
Uses & applications
Crushed basalt is used for road aggregate, concrete, railroad ballast, and building stone; attractive vesicular pieces are collected as volcanic specimens. It is generally unsuitable for jewelry unless polished or mineral-filled.
Geological facts
Vesicles are bubbles preserved in lava as dissolved gases escaped during cooling. It may resemble pumice, but basalt is denser and less porous, while pumice is typically much lighter and often floats.
Field identification & locations
Identify it by its fine texture, dense weight, irregular cavities, and lack of visible sedimentary layering; a streak is usually pale gray. Common sources include volcanic regions such as Iceland, Hawaii, Mexico, the western United States, and oceanic islands.
