igneous
Vesicular basalt
Basalt, a fine-grained mafic volcanic rock composed mainly of plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectTypically dark gray to black, here weathered reddish-brown, with abundant gas vesicles and dull to weakly vitreous luster; hardness about 5–6 Mohs, massive texture, and no obvious cleavage. The cavities may contain secondary iron oxides or zeolite minerals.
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Physical properties
Typically dark gray to black, here weathered reddish-brown, with abundant gas vesicles and dull to weakly vitreous luster; hardness about 5–6 Mohs, massive texture, and no obvious cleavage. The cavities may contain secondary iron oxides or zeolite minerals.
Formation & geological history
Formed when basaltic lava rapidly cooled at or near Earth’s surface, trapping volcanic gas bubbles; likely Cenozoic or younger, though age cannot be determined from the image. Common in lava flows, volcanic fields, oceanic crust, and basalt quarries.
Uses & applications
Used as crushed aggregate, road base, riprap, ballast, and building stone; attractive polished pieces are occasionally sold as landscaping or display specimens.
Geological facts
The reddish coloration generally reflects oxidation of iron-bearing minerals during weathering. Its vesicles distinguish it from most intrusive igneous rocks such as gabbro.
Field identification & locations
Identify it by its fine-grained dark matrix, heavy weight, angular fracture, and abundant rounded cavities; a streak test is usually gray, and it is not noticeably reactive with dilute hydrochloric acid. Common worldwide, especially in Hawaii, Iceland, India’s Deccan Traps, and oceanic volcanic regions.
