igneous
Vesicular basalt (likely weathered volcanic rock)
Vesicular basalt; predominantly plagioclase, pyroxene, and possibly olivine, with secondary zeolite or calcite infill
AI-generated identification · may be incorrectDark gray-brown to cream, fine-grained volcanic matrix with abundant rounded vesicles and pale secondary mineral coatings; typically Mohs 5–6, dull to mildly vitreous luster, no strong cleavage, and specific gravity about 2.7–3.0.
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Physical properties
Dark gray-brown to cream, fine-grained volcanic matrix with abundant rounded vesicles and pale secondary mineral coatings; typically Mohs 5–6, dull to mildly vitreous luster, no strong cleavage, and specific gravity about 2.7–3.0.
Formation & geological history
Formed when gas-rich basaltic lava rapidly cooled, trapping bubbles; later groundwater deposited pale zeolites, calcite, or silica in the cavities. The specimen’s exact geological age cannot be determined from the photograph.
Uses & applications
Used mainly as a teaching or collector specimen; basalt is widely used for aggregate, roadstone, riprap, and sometimes dimension stone, while cavity minerals may add display value.
Geological facts
The porous texture is called vesicular; if the cavities are heavily filled with minerals, the material may be marketed as an amygdaloidal basalt or volcanic geode.
Field identification & locations
Identify it by its heavy volcanic matrix, abundant cavities, and dark mafic fragments surrounded by pale coatings. Common in lava flows and volcanic regions worldwide, including India, Iceland, Oregon, Mexico, and the western United States.
