igneous
Vesicular basalt with a pale mineral vesicle filling
Basalt, likely amygdaloidal basalt; pale filling may be calcite, zeolite, or quartz
AI-generated identification · may be incorrectDark gray-black, fine-grained and highly vesicular, with a dull to faintly vitreous luster; hardness about 5–6 for basalt, while the filling may vary from 3 (calcite) to 7 (quartz). Basalt is composed mainly of plagioclase, pyroxene, and commonly olivine; no obvious cleavage is visible.
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Physical properties
Dark gray-black, fine-grained and highly vesicular, with a dull to faintly vitreous luster; hardness about 5–6 for basalt, while the filling may vary from 3 (calcite) to 7 (quartz). Basalt is composed mainly of plagioclase, pyroxene, and commonly olivine; no obvious cleavage is visible.
Formation & geological history
Formed when mafic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles; the pale patch later filled a vesicle with secondary minerals from circulating fluids. Basalt ranges from Precambrian to modern, and its exact age cannot be determined from the photograph.
Uses & applications
Used widely as crushed aggregate, road stone, building stone, and occasionally as decorative material; attractive amygdaloidal pieces are collected. Value is typically $5–$25 for a hand specimen, or up to $30–$100 if the mineral filling is attractive and identified.
Geological facts
Common in volcanic islands, lava flows, oceanic crust, and flood-basalt provinces. The holes indicate gas-rich lava, while the lighter patch is an amygdule rather than the original basalt texture.
Field identification & locations
Identify it by its black porous volcanic texture and relatively heavy weight; acid testing can distinguish calcite filling (effervescence), while a steel scratch test helps estimate hardness. Common localities include Hawaii, Iceland, India, the Columbia River Basalt region, and many volcanic terrains.
