metamorphic
Banded metamorphic rock, likely banded gneiss
Gneiss, probably biotite–quartz–feldspar gneiss
AI-generated identification · may be incorrectDark gray-brown, strongly foliated and compositional-banded, with mica-rich layers producing a glittery luster; typical hardness is about 6–7 Mohs, with no prominent cleavage as a whole and variable specific gravity around 2.6–2.8.
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Physical properties
Dark gray-brown, strongly foliated and compositional-banded, with mica-rich layers producing a glittery luster; typical hardness is about 6–7 Mohs, with no prominent cleavage as a whole and variable specific gravity around 2.6–2.8.
Formation & geological history
Formed when preexisting igneous or sedimentary rock underwent high-grade metamorphism, causing minerals to recrystallize and segregate into bands; such rocks commonly record Precambrian to Paleozoic crustal events.
Uses & applications
Used as dimension stone, paving and landscaping material, aggregate, and occasionally as decorative slabs; attractive specimens have modest collector value.
Geological facts
The alternating light and dark bands reflect mineral separation during intense heat and pressure, not sedimentary layering. The image is insufficient to distinguish gneiss confidently from strongly foliated schist or banded amphibolite.
Field identification & locations
Look for alternating quartz/feldspar-rich and dark mica/amphibole-rich bands, sparkly mica, and a hard crystalline texture; common in ancient continental shields and metamorphic mountain belts. Approximate value: $5–$30 for a hand specimen, or more if unusually attractive and polished.
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