igneous
Weathered quartz-rich cobble, possibly granitic gneiss
Probable quartz–feldspar–mica aggregate; exact lithology uncertain from image
AI-generated identification · may be incorrectGray-brown, fine- to medium-grained, dull to slightly vitreous; likely quartz and feldspar with dark mica or amphibole. Hardness approximately 6–7 Mohs, massive with no obvious cleavage, and rounded by abrasion and weathering.
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Physical properties
Gray-brown, fine- to medium-grained, dull to slightly vitreous; likely quartz and feldspar with dark mica or amphibole. Hardness approximately 6–7 Mohs, massive with no obvious cleavage, and rounded by abrasion and weathering.
Formation & geological history
Likely formed by slow crystallization of silica-rich magma, or metamorphic recrystallization if weak foliation is present, then exposed and rounded in a stream, beach, or glacial deposit. Its geological age cannot be determined visually and may range from Precambrian to recent source-rock erosion.
Uses & applications
Commonly used as landscaping stone, aggregate, and decorative cobble; this small weathered specimen has minimal commercial value but can be useful for teaching rock identification.
Geological facts
The pitted surface reflects differential weathering: softer feldspar or dark minerals weather faster than quartz. A fresh broken surface would be needed to distinguish granite, granitic gneiss, or another quartz-rich rock confidently.
Field identification & locations
Look for glassy gray quartz, blocky white or pink feldspar, and black mica; visible banding would favor gneiss, while random interlocking grains favor granite. Common worldwide in continental uplands and sedimentary gravel deposits.
