igneous
Weathered granite or granitic gneiss cobble
Quartz–feldspar–mica granitoid; exact identification requires a fresh surface or testing
AI-generated identification · may be incorrectCoarse, uneven granular texture with pale quartz/feldspar and darker mica or mafic minerals; dull earthy luster from weathering. Likely Mohs hardness 6–7, no obvious cleavage as a whole rock, and moderate-to-high specific gravity around 2.6–2.8.
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Physical properties
Coarse, uneven granular texture with pale quartz/feldspar and darker mica or mafic minerals; dull earthy luster from weathering. Likely Mohs hardness 6–7, no obvious cleavage as a whole rock, and moderate-to-high specific gravity around 2.6–2.8.
Formation & geological history
Probably crystallized slowly from silica-rich magma deep in the crust, commonly during Precambrian to younger continental mountain-building events, then exposed and rounded by erosion. The brown-gray surface reflects oxidation and weathering.
Uses & applications
Common granite is used for crushed aggregate, building stone, paving, monuments, and countertops; an ordinary cobble has little commercial value.
Geological facts
The image does not show diagnostic crystal faces or layering, so granite, gneiss, and weathered other silicate rocks cannot be separated confidently from appearance alone.
Field identification & locations
Look for visible interlocking quartz and feldspar grains; gneiss would show clear mineral banding. A glassy quartz grain should scratch glass, while feldspar commonly shows two cleavage directions; dilute acid should not fizz. Common worldwide, especially continental shields and mountain belts.
