metamorphic

Tumbled banded metamorphic stone

Likely banded gneiss or migmatitic gneiss; exact identification requires testing

AI-generated identification · may be incorrect

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.

Identified August 8, 2026More metamorphic →

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Physical properties

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.