metamorphic
Banded metamorphic rock, likely gneiss
Biotite–quartz–feldspar gneiss, possibly migmatitic
AI-generated identification · may be incorrectTypically Mohs 6–7; dark gray to silvery with alternating light and dark bands, vitreous to dull luster, and a foliated/crystalline texture. Likely minerals include quartz, feldspar, mica, and possibly hornblende; visible layering reflects mineral alignment.
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Physical properties
Typically Mohs 6–7; dark gray to silvery with alternating light and dark bands, vitreous to dull luster, and a foliated/crystalline texture. Likely minerals include quartz, feldspar, mica, and possibly hornblende; visible layering reflects mineral alignment.
Formation & geological history
Formed when preexisting igneous or sedimentary rock underwent intense heat and pressure, commonly during mountain building. Such rocks are usually Precambrian to Paleozoic, though exact age cannot be determined from the photograph.
Uses & applications
Used as dimension stone, paving, aggregate, landscaping rock, and decorative polished stone; attractive pieces may be collected but are generally low value.
Geological facts
The banding is metamorphic foliation, not sedimentary bedding, and may show folded or stretched layers. The specimen appears weathered and naturally fractured rather than gem quality.
Field identification & locations
Look for continuous mineral bands, mica sparkle, hard quartz-rich grains, and a tendency to split along foliation; it should scratch glass but not be scratched by a steel nail. Common in ancient continental shields and metamorphic mountain belts.
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