igneous
Vesicular basalt
Basalt, chiefly plagioclase, pyroxene, and olivine
AI-generated identification · may be incorrectDark gray-brown, fine-grained, rough and locally vesicular with a dull to weakly glassy luster; hardness about 6, with no prominent cleavage. The granular pale crystals may be plagioclase or weathered zeolite fillings.
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Physical properties
Dark gray-brown, fine-grained, rough and locally vesicular with a dull to weakly glassy luster; hardness about 6, with no prominent cleavage. The granular pale crystals may be plagioclase or weathered zeolite fillings.
Formation & geological history
An extrusive volcanic rock formed when mafic lava cooled rapidly at or near Earth’s surface, commonly during the Cenozoic or older volcanic episodes. Vesicles formed from gas bubbles trapped in the cooling lava and may later become mineral-filled.
Uses & applications
Used extensively as crushed aggregate, road base, railway ballast, riprap, and building stone; attractive polished pieces are occasionally collected. This rough specimen has little commercial value.
Geological facts
Basalt is the most widespread volcanic rock and forms much of oceanic crust, including mid-ocean ridges and many volcanic islands.
Field identification & locations
Identify it by its dark color, heavy feel, fine texture, and scattered holes or pale mineral grains; a streak test is usually gray, and it commonly attracts no magnet or only weakly. Common localities include Hawaii, Iceland, India’s Deccan Traps, and oceanic volcanic regions.
