metamorphic
Rounded granitic gneiss cobble
Foliated granitoid gneiss, chiefly quartz, feldspar, and mica
AI-generated identification · may be incorrectCoarse-grained, pale gray-tan rock with visible quartz/feldspar speckling and weak foliation; likely Mohs 6–7, vitreous to dull luster, poor cleavage overall, and specific gravity about 2.6–2.7.
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Physical properties
Coarse-grained, pale gray-tan rock with visible quartz/feldspar speckling and weak foliation; likely Mohs 6–7, vitreous to dull luster, poor cleavage overall, and specific gravity about 2.6–2.7.
Formation & geological history
Formed by high-grade metamorphism of granite or related igneous rock, commonly during Precambrian to Paleozoic mountain-building; rounded by stream or glacial transport and weathering.
Uses & applications
Used locally as landscaping stone, riprap, aggregate, and building veneer; this ordinary weathered cobble has little jewelry or collector value.
Geological facts
The image shows a large, water-worn cobble among darker rounded river stones. Its granular quartz-feldspar texture distinguishes it from basalt, while subtle mineral alignment suggests gneiss rather than massive granite.
Field identification & locations
Identify it by its hard, speckled quartz-feldspar surface, occasional mica flakes, and inability to scratch with a steel knife; it commonly occurs in glacial tills and river gravels derived from crystalline bedrock.
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