metamorphic
Gneiss
Quartz–feldspar–biotite gneiss
AI-generated identification · may be incorrectCoarse-grained, gray and cream, with dark biotite-rich streaks and weak foliation; quartz and feldspar are about Mohs 6–7, with vitreous quartz and pearly feldspar luster. The visible minerals suggest gneissic banding, though the specimen’s texture is irregular.
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Physical properties
Coarse-grained, gray and cream, with dark biotite-rich streaks and weak foliation; quartz and feldspar are about Mohs 6–7, with vitreous quartz and pearly feldspar luster. The visible minerals suggest gneissic banding, though the specimen’s texture is irregular.
Formation & geological history
Formed when pre-existing igneous or sedimentary rock underwent high-grade heat and pressure, commonly deep in continental crust; ages range from ancient Archean rocks to younger mountain belts.
Uses & applications
Used as dimension stone, paving, aggregate, and landscaping stone; attractive pieces may be collected or used decoratively.
Geological facts
Gneiss is identified by coarse mineral segregation or banding, rather than the thin splitting typical of schist.
Field identification & locations
Look for interlocking light quartz/feldspar and darker mica or amphibole arranged in streaks; common in ancient continental shields and mountain cores. The photo supports a likely gneiss identification, but a close mineral examination would improve certainty.
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