igneous
Vesicular basalt (weathered volcanic scoria)
Basalt, predominantly plagioclase feldspar and clinopyroxene with possible olivine; vesicular texture
AI-generated identification · may be incorrectDark gray to brown, fine-grained, strongly vesicular, with dull to slightly glassy luster and no obvious cleavage. Hardness is about 5–6 Mohs; individual vesicles are gas cavities, some partly weathered or mineral-filled.
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Physical properties
Dark gray to brown, fine-grained, strongly vesicular, with dull to slightly glassy luster and no obvious cleavage. Hardness is about 5–6 Mohs; individual vesicles are gas cavities, some partly weathered or mineral-filled.
Formation & geological history
Formed when gas-rich mafic lava rapidly cooled at or near the surface, commonly in a Holocene-to-Cenozoic volcanic field; the exact age cannot be determined from the image. Weathering has enlarged or softened some cavities.
Uses & applications
Used as lightweight aggregate, landscaping stone, drainage material, and occasionally as a lapidary or teaching specimen; generally not gem-grade.
Geological facts
Its abundant rounded holes distinguish vesicular basalt or scoria from dense basalt. The pale weathering crust and possible reddish patches may reflect oxidation of iron-bearing minerals.
Field identification & locations
Identify it by its low density, dark fine-grained matrix, abundant irregular vesicles, and lack of visible sedimentary layering; common near volcanic cones, lava flows, and cinder fields. A hand lens and streak, hardness, and magnetic tests can help confirm basalt.
