igneous
Vesicular basalt (probable)
Basalt; chiefly plagioclase feldspar, clinopyroxene, and iron-rich minerals, with vesicles possibly lined by zeolites or calcite
AI-generated identification · may be incorrectDark gray, fine-grained, dull to slightly glassy, irregular and strongly vesicular; hardness about 5–6 Mohs, no obvious cleavage, and typical specific gravity around 2.7–3.0. The rounded pale cavities may be secondary mineral fillings or weathered vesicles.
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Physical properties
Dark gray, fine-grained, dull to slightly glassy, irregular and strongly vesicular; hardness about 5–6 Mohs, no obvious cleavage, and typical specific gravity around 2.7–3.0. The rounded pale cavities may be secondary mineral fillings or weathered vesicles.
Formation & geological history
An extrusive volcanic rock formed when basaltic lava cooled rapidly at or near Earth’s surface, commonly during Cenozoic to recent volcanic activity. Vesicles formed from trapped gas bubbles during eruption.
Uses & applications
Used as crushed aggregate, road base, riprap, and landscaping stone; attractive zeolite- or calcite-filled specimens are collected but are rarely valuable.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust and commonly forms lava flows, pillow lavas, and volcanic islands.
Field identification & locations
Identify it by its dark fine-grained matrix, high density, and abundant rounded holes; a steel nail generally will not scratch fresh basalt. Common localities include Hawaii, Iceland, the Pacific Northwest, India’s Deccan Traps, and oceanic islands.
