igneous
Weathered vesicular basalt
Basalt, a mafic volcanic rock composed mainly of plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray to brown, fine-grained, rough and locally vesicular with weathering rind; typically glassy to dull luster, no visible cleavage, hardness about 5–6 Mohs, and specific gravity around 2.8–3.0.
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Physical properties
Dark gray to brown, fine-grained, rough and locally vesicular with weathering rind; typically glassy to dull luster, no visible cleavage, hardness about 5–6 Mohs, and specific gravity around 2.8–3.0.
Formation & geological history
Formed when basaltic lava cooled rapidly at or near Earth’s surface, likely during a relatively young volcanic episode; the pale, rusty surface reflects oxidation and chemical weathering. Exact age and locality cannot be determined from the image.
Uses & applications
Used as crushed aggregate, road metal, riprap, railroad ballast, and building stone; attractive polished pieces may be used decoratively, though this specimen appears ordinary and heavily weathered.
Geological facts
Basalt is the most abundant volcanic rock on Earth and forms much of the oceanic crust. Vesicles are gas bubbles preserved during lava cooling.
Field identification & locations
Identify it by its dark fine-grained matrix, substantial weight, lack of obvious quartz, and scattered gas cavities; common in volcanic regions, lava fields, and stream gravels. The pictured rock may also be weathered scoria or an altered basaltic fragment.
