igneous
Weathered volcanic rock, likely andesite or basalt
Fine-grained mafic to intermediate volcanic rock; commonly plagioclase ± pyroxene, amphibole, and iron oxides
AI-generated identification · may be incorrectDark brown-gray, dull to weakly earthy luster, irregular granular texture, and no obvious cleavage; estimated Mohs hardness 5–6. The surface appears heavily weathered, making crystal identification difficult.
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Physical properties
Dark brown-gray, dull to weakly earthy luster, irregular granular texture, and no obvious cleavage; estimated Mohs hardness 5–6. The surface appears heavily weathered, making crystal identification difficult.
Formation & geological history
Formed when lava cooled relatively quickly at or near Earth’s surface, generally during Cenozoic or older volcanic activity; the specimen’s exact age cannot be determined visually.
Uses & applications
Primarily used as aggregate, roadstone, riprap, and building material; this small weathered fragment has negligible jewelry or commercial value.
Geological facts
Its brown coloration likely reflects oxidation of iron-bearing minerals during weathering. Vesicles are not clearly visible, so it is less likely to be pumice or scoria.
Field identification & locations
Common in volcanic regions worldwide, including the Pacific Ring of Fire, western North America, Iceland, and Mediterranean areas. A streak test, fresh broken surface, magnetism test, and thin-section analysis would help distinguish basalt from andesite.
