igneous
Quartz-rich granite or granitic gneiss
Granite; predominantly quartz (SiO₂), feldspar, and minor mica/mafic minerals
AI-generated identification · may be incorrectCoarse, massive granular texture with white-gray quartz/feldspar and darker mineral patches; vitreous to dull luster, no obvious cleavage in quartz, Mohs hardness about 6–7, and specific gravity roughly 2.6–2.7. The rounded shape indicates natural weathering or tumbling.
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Physical properties
Coarse, massive granular texture with white-gray quartz/feldspar and darker mineral patches; vitreous to dull luster, no obvious cleavage in quartz, Mohs hardness about 6–7, and specific gravity roughly 2.6–2.7. The rounded shape indicates natural weathering or tumbling.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep in the continental crust, commonly during Precambrian to younger continental igneous events; the image could also represent mildly foliated granitic gneiss. Exact identification requires a fresh broken surface or testing.
Uses & applications
Commonly used as crushed stone, aggregate, building stone, countertops, monuments, and landscaping rock; this small weathered piece has little jewelry value.
Geological facts
Quartz appears translucent to gray and glassy, while feldspar is generally opaque and blocky; darker grains may be biotite or hornblende. A knife should not scratch fresh quartz, but glass can scratch many feldspars.
Field identification & locations
Common worldwide, especially in continental shields and mountain belts; test with a steel nail, inspect grain interlocking, and use dilute acid to exclude limestone. Common local specimens are typically worth $1–$10, or up to about $20 if unusually attractive or labeled with provenance.
