igneous
Weathered granite or granitic gneiss cobble
Quartz–feldspar–mica aggregate, likely granite; possible weakly foliated gneiss
AI-generated identification · may be incorrectCoarse, gray-green, granular rock with pale/tan feldspar patches and dark mica or amphibole; dull to slightly sparkly luster, no obvious cleavage as a whole, Mohs hardness about 6–7, and specific gravity roughly 2.6–2.8.
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Physical properties
Coarse, gray-green, granular rock with pale/tan feldspar patches and dark mica or amphibole; dull to slightly sparkly luster, no obvious cleavage as a whole, Mohs hardness about 6–7, and specific gravity roughly 2.6–2.8.
Formation & geological history
Formed by slow cooling of silica-rich magma deep in the crust, generally Precambrian to Mesozoic in age depending on locality; surface weathering has rounded and darkened the cobble.
Uses & applications
Granite is widely used as crushed aggregate, building stone, countertops, monuments, and paving; this small weathered specimen has modest educational or display value.
Geological facts
The tan areas are likely weathered feldspar, while gray translucent grains may be quartz. A definitive identification requires a fresh surface, hand lens, and locality information.
Field identification & locations
Look for interlocking quartz and feldspar grains, scattered dark minerals, and strong resistance to scratching; it should not fizz with dilute hydrochloric acid. Common in continental mountain belts, glacial deposits, streambeds, and construction fill.
