metamorphic
Tumbled banded metamorphic stone
Likely banded gneiss or migmatitic gneiss; exact identification requires testing
AI-generated identification · may be incorrectDark gray-brown, fine-to-medium grained, with pale and dark mineral bands and a subdued vitreous-to-earthy luster. Typical hardness is about 6–7 Mohs; quartz and feldspar dominate, with mica or amphibole possible; cleavage is weak or absent as a whole rock.
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Physical properties
Dark gray-brown, fine-to-medium grained, with pale and dark mineral bands and a subdued vitreous-to-earthy luster. Typical hardness is about 6–7 Mohs; quartz and feldspar dominate, with mica or amphibole possible; cleavage is weak or absent as a whole rock.
Formation & geological history
Formed when preexisting rock underwent intense heat and pressure, producing compositional banding; commonly Precambrian to Paleozoic in age. The rounded shape and smooth surface indicate human tumbling/polishing.
Uses & applications
Used as a decorative stone, paperweight, landscaping material, and jewelry or cabochon rough; generally not valued as a gemstone.
Geological facts
Gneissic banding records mineral segregation during metamorphism and can resemble striped granite. The dark vertical streaks may reflect biotite-rich or amphibole-rich layers.
Field identification & locations
Look for alternating light quartz-feldspar layers and darker mica/amphibole layers, plus a crystalline rather than glassy texture; a steel file should not easily scratch quartz-rich areas. Common sources include metamorphic terrains worldwide, including Scandinavia, Canada, the United States, India, and Brazil.
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