igneous
Vesicular basalt (likely scoria)
Vesicular basalt; predominantly plagioclase, pyroxene, and possibly olivine
AI-generated identification · may be incorrectDark gray-brown, fine-grained, dull to slightly glassy, with abundant gas vesicles; hardness about 5–6 Mohs, no visible cleavage, and typically high density except for its pores. The rounded shape appears water-worn or weathered.
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Physical properties
Dark gray-brown, fine-grained, dull to slightly glassy, with abundant gas vesicles; hardness about 5–6 Mohs, no visible cleavage, and typically high density except for its pores. The rounded shape appears water-worn or weathered.
Formation & geological history
An extrusive volcanic rock formed when basaltic lava cooled rapidly while escaping gas created cavities. Commonly Quaternary to modern in age, especially near cinder cones, lava flows, and volcanic islands.
Uses & applications
Used as lightweight aggregate, landscaping stone, drainage material, and occasionally abrasive or decorative stone; generally low gem or collector value.
Geological facts
Scoria is usually more reddish and porous, while basalt is commonly darker and denser; this specimen may be transitional between the two. Vesicles can later become filled with secondary minerals such as zeolite or calcite.
Field identification & locations
Identify it by its dark fine-grained matrix, numerous irregular holes, and lack of layered sedimentary structure; it is common in Hawaii, Iceland, Japan, the western United States, and other volcanic regions. A magnet may show weak attraction if iron-rich.
