igneous
Weathered volcanic rock fragment
Likely andesite or basalt; exact identification requires fresh surface and testing
AI-generated identification · may be incorrectGray-brown, fine-grained, dull to slightly earthy luster, with dark mineral patches and irregular fracture; likely Mohs hardness 5–6, no obvious cleavage, and specific gravity about 2.6–2.9.
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Physical properties
Gray-brown, fine-grained, dull to slightly earthy luster, with dark mineral patches and irregular fracture; likely Mohs hardness 5–6, no obvious cleavage, and specific gravity about 2.6–2.9.
Formation & geological history
An igneous rock formed when iron- and magnesium-bearing lava cooled, probably rapidly at or near Earth’s surface. Its weathered appearance reflects later oxidation and environmental alteration; age cannot be determined visually.
Uses & applications
Common volcanic rock is used as crushed aggregate, road material, riprap, and sometimes building stone. This small weathered fragment has little commercial or collector value.
Geological facts
Basalt is typically darker and richer in pyroxene, while andesite is commonly medium gray and contains more feldspar. The specimen’s brown coloration likely comes from weathering of iron-bearing minerals.
Field identification & locations
Common in volcanic regions, including the Pacific Ring of Fire, oceanic crust, and ancient lava fields. A fresh break, acid test, hand lens, streak, and density comparison can distinguish it from sandstone or concrete.
