igneous
Unidentified weathered rock, possibly quartz-bearing granite or rhyolite
Indeterminate; likely quartz–feldspar-rich silicate rock
AI-generated identification · may be incorrectGray-tan, irregular and fine-to-medium grained with a dull to slightly granular luster; apparent hardness about 6–7 Mohs if quartz-rich. Crystal structure and cleavage are not reliably visible from the photograph.
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Physical properties
Gray-tan, irregular and fine-to-medium grained with a dull to slightly granular luster; apparent hardness about 6–7 Mohs if quartz-rich. Crystal structure and cleavage are not reliably visible from the photograph.
Formation & geological history
Likely formed by cooling of silica-rich magma, either underground (granite) or at the surface (rhyolite); its geological age cannot be determined visually. Surface weathering has produced the rough, rounded exterior.
Uses & applications
Unprocessed material has little industrial or jewelry value, though comparable granite and rhyolite are used as aggregate, building stone, and decorative rock.
Geological facts
The specimen may also be a weathered quartz vein fragment or another common silicate rock; a fresh broken surface and magnification would substantially improve identification.
Field identification & locations
Look for visible interlocking quartz and feldspar grains for granite, or a very fine matrix for rhyolite; a streak test, hardness test, acid test, and hand lens are useful. Common worldwide in continental volcanic and plutonic terrains.
