metamorphic
Tumbled gneiss or granite pebble
Feldspar–quartz–mica rock; likely biotite gneiss (identification uncertain from image)
AI-generated identification · may be incorrectDark gray-blue, rounded and polished, with glittery mica and lighter mineral patches. Likely hardness 6–7 Mohs, nonmetallic luster, granular crystalline texture, no obvious cleavage as a whole rock; density about 2.6–2.8 g/cm³.
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Physical properties
Dark gray-blue, rounded and polished, with glittery mica and lighter mineral patches. Likely hardness 6–7 Mohs, nonmetallic luster, granular crystalline texture, no obvious cleavage as a whole rock; density about 2.6–2.8 g/cm³.
Formation & geological history
If gneiss, it formed by high-grade metamorphism of an older felsic rock during deep burial; if granite, it crystallized slowly from magma. The specimen’s geological age cannot be determined visually and may range from Precambrian to younger.
Uses & applications
Commonly used as a decorative tumbled stone, landscaping aggregate, and occasionally construction aggregate; generally little jewelry or collector value.
Geological facts
The sparkle likely comes from mica, while pale areas may be quartz or feldspar. Its rounded shape indicates natural stream wear or deliberate tumbling.
Field identification & locations
Look for interlocking grains, pale quartz/feldspar, and reflective mica flakes; distinct banding would support gneiss, while a more uniform texture suggests granite. Common worldwide, especially in continental shields and granitic terrains.
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