igneous
Weathered gray rock, likely basaltic or andesitic fragment
Fine-grained mafic to intermediate volcanic rock; exact identification requires fresh surface and testing
AI-generated identification · may be incorrectDark gray-brown, dull to weakly earthy luster, massive and fine-grained with weathering crust; likely hardness about 5–6 Mohs, no obvious cleavage, and moderate density around 2.7–3.0 g/cm³.
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Physical properties
Dark gray-brown, dull to weakly earthy luster, massive and fine-grained with weathering crust; likely hardness about 5–6 Mohs, no obvious cleavage, and moderate density around 2.7–3.0 g/cm³.
Formation & geological history
Probably formed when lava cooled rapidly at or near Earth’s surface, then weathered and rounded by erosion; its geological age cannot be determined from the photograph.
Uses & applications
Common basalt and andesite are used as crushed aggregate, roadstone, riprap, and building stone; an ordinary fragment has negligible commercial or jewelry value.
Geological facts
The pale gray surface may reflect oxidation, alteration, or adhered soil rather than the rock’s fresh color. Basalt is typically richer in iron and magnesium, whereas andesite is compositionally intermediate and may contain visible feldspar.
Field identification & locations
Look for a freshly broken surface, magnetic response, vesicles, and crystal size; basalt is commonly weakly magnetic and dark, while andesite is often lighter gray. Common worldwide in volcanic regions; professional identification may require microscopy or chemical analysis.
