igneous
Vesicular basalt
Basalt, a mafic volcanic rock composed mainly of plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray-brown, fine-grained, dull to slightly glassy, with tiny vesicles and weathered rusty surfaces; hardness about 5–6 Mohs, massive structure, poor cleavage, and specific gravity roughly 2.7–3.1.
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Physical properties
Dark gray-brown, fine-grained, dull to slightly glassy, with tiny vesicles and weathered rusty surfaces; hardness about 5–6 Mohs, massive structure, poor cleavage, and specific gravity roughly 2.7–3.1.
Formation & geological history
Formed when low-silica basaltic lava cooled rapidly at or near Earth’s surface, commonly in flows, dikes, or volcanic islands; its exact age cannot be determined from the image and may range from ancient to recent.
Uses & applications
Used as crushed aggregate, road base, railway ballast, riprap, and building stone; attractive polished pieces may be collected, though this specimen appears ordinary rather than gem-grade.
Geological facts
Basalt is the most abundant volcanic rock on Earth and makes up much of the oceanic crust. Vesicles formed when dissolved volcanic gases escaped during cooling.
Field identification & locations
Identify it by its dark color, fine texture, heavy feel, and possible gas bubbles; magnetism may occur if magnetite is present. Common worldwide in volcanic regions, including Hawaii, Iceland, India, and oceanic crust.
