igneous
Weathered basaltic rock (probable vesicular basalt)
Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine, with iron-oxide alteration
AI-generated identification · may be incorrectDark gray-green, fine-grained, dull to slightly earthy luster, with small vesicles and rusty oxidation spots; hardness about 5–6 Mohs, massive with no obvious cleavage, specific gravity roughly 2.8–3.0.
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Physical properties
Dark gray-green, fine-grained, dull to slightly earthy luster, with small vesicles and rusty oxidation spots; hardness about 5–6 Mohs, massive with no obvious cleavage, specific gravity roughly 2.8–3.0.
Formation & geological history
An extrusive igneous rock formed when basaltic lava cooled rapidly at or near Earth’s surface; its exact geologic age cannot be determined from the photograph, and weathering has produced the brown-red iron staining.
Uses & applications
Commonly used as crushed aggregate, road base, riprap, railroad ballast, and occasionally building or landscaping stone; generally has little jewelry value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and forms much of the oceanic crust. Vesicles record gas bubbles trapped during lava cooling, while green coloration may reflect altered basaltic minerals.
Field identification & locations
Look for a dense, dark fine-grained matrix, scattered vesicles, and weak magnetism from iron-bearing minerals; distinguish it from slag by its natural crystalline texture and lack of glassy flow surfaces. Common in volcanic regions and former lava flows.
