igneous
Vesicular basalt (scoriaceous basalt)
Basalt; predominantly plagioclase, clinopyroxene, and olivine with iron oxides
AI-generated identification · may be incorrectDark gray, fine-grained to partly porphyritic, rough and locally vesicular, with dull to slightly vitreous luster; Mohs hardness about 5–6, no cleavage as a rock, specific gravity roughly 2.7–3.0.
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Physical properties
Dark gray, fine-grained to partly porphyritic, rough and locally vesicular, with dull to slightly vitreous luster; Mohs hardness about 5–6, no cleavage as a rock, specific gravity roughly 2.7–3.0.
Formation & geological history
An extrusive mafic igneous rock formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface. Comparable basalt may range from recent volcanic flows to ancient oceanic crust, but the specimen’s age cannot be determined from the image.
Uses & applications
Used as aggregate, road base, riprap, railroad ballast, and dimension stone; attractive pieces may be collected, though it is not normally a jewelry material.
Geological facts
The abundant cavities indicate gas bubbles trapped during lava cooling; weathering or alteration may fill them with zeolites, calcite, or quartz.
Field identification & locations
Identify it by its black-gray color, heavy feel, fine texture, and irregular vesicles; common in volcanic regions, oceanic crust, Hawaii, Iceland, the Pacific Northwest, and many continental flood basalts.
