igneous
Weathered basaltic volcanic rock
Likely vesicular basalt or basaltic-andesite; chiefly plagioclase, pyroxene, and iron-bearing minerals
AI-generated identification · may be incorrectDark brown-gray, fine-grained and rough with irregular vesicles or weathered cavities; typically dull to slightly subvitreous luster, no obvious cleavage, hardness about 5–6, and specific gravity roughly 2.7–3.1.
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Physical properties
Dark brown-gray, fine-grained and rough with irregular vesicles or weathered cavities; typically dull to slightly subvitreous luster, no obvious cleavage, hardness about 5–6, and specific gravity roughly 2.7–3.1.
Formation & geological history
Formed when mafic lava cooled rapidly at or near Earth’s surface, likely during a relatively recent volcanic episode; surface oxidation and alteration produced the brown coloration. Exact age and identification require fresh-surface examination and testing.
Uses & applications
Common basalt is used as crushed aggregate, road base, riprap, ballast, and dimension stone; attractive specimens may be kept for geological collections but usually have modest value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and forms much of the oceanic crust. Vesicles indicate gas bubbles trapped during lava cooling, though the cavities here may also be weathering pits.
Field identification & locations
Look for a dark fine-grained matrix, abundant plagioclase or pyroxene, high density, and possible weak magnetism; basalt commonly occurs in lava flows, volcanic islands, and oceanic crust. Estimated value: $5–$30 for a common hand specimen, occasionally $50–$100 if unusually textured or provenance-labeled.
