igneous
Weathered basaltic volcanic rock
Basalt, likely vesicular/amygdaloidal basalt
AI-generated identification · may be incorrectDark gray to black, fine-grained, dull to slightly vitreous luster, with abundant rounded weathering cavities (vesicles). Basalt typically has Mohs hardness 6, no visible cleavage, specific gravity about 2.8–3.0, and consists mainly of plagioclase and pyroxene with possible olivine or iron oxides.
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Physical properties
Dark gray to black, fine-grained, dull to slightly vitreous luster, with abundant rounded weathering cavities (vesicles). Basalt typically has Mohs hardness 6, no visible cleavage, specific gravity about 2.8–3.0, and consists mainly of plagioclase and pyroxene with possible olivine or iron oxides.
Formation & geological history
Formed when mafic lava cooled rapidly at or near Earth’s surface, likely during a Cenozoic or older volcanic eruption; the exact age cannot be determined from the photograph. Cavities formed from trapped gas and were later enlarged or accentuated by weathering and erosion.
Uses & applications
Used as crushed aggregate, road base, riprap, railroad ballast, paving stone, and building stone; attractive polished pieces may be used decoratively. This rough exposure has little specimen value.
Geological facts
The holes are vesicles or weathering pits, not necessarily fossils. Brown-orange patches likely represent iron-oxide staining, while lighter zones may be altered minerals or weathered surfaces.
Field identification & locations
Identify by its dark, dense, fine texture, heavy weight, and lack of visible quartz grains; a streak, fresh broken surface, and magnet test can help confirm it. Common in volcanic regions, oceanic crust, Hawaii, Iceland, the Pacific Northwest, and continental basalt provinces.
