igneous
Weathered granite or granitic gneiss cobble
Granite; chiefly quartz, feldspar, and mica
AI-generated identification · may be incorrectCoarse, speckled gray-brown rock with visible light feldspar/quartz and dark mica or mafic minerals; typically Mohs 6–7, vitreous to dull luster, interlocking crystals, and no prominent cleavage as a whole.
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Physical properties
Coarse, speckled gray-brown rock with visible light feldspar/quartz and dark mica or mafic minerals; typically Mohs 6–7, vitreous to dull luster, interlocking crystals, and no prominent cleavage as a whole.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep in the crust, then exposed by uplift and erosion; the specimen is heavily weathered, and its exact age cannot be determined from the image.
Uses & applications
Commonly used as aggregate, riprap, paving stone, monuments, and dimension stone; this weathered cobble has little commercial or jewelry value.
Geological facts
The granular texture reflects slow cooling underground. Brown coloration commonly results from oxidation of iron-bearing minerals and surface weathering.
Field identification & locations
Identify it by its visible interlocking quartz-feldspar-mica grains, hardness, and lack of layering; common in continental crust, glacial deposits, streambeds, and construction fill. The surrounding material appears to be gravelly aggregate or beach sediment.
