metamorphic
Coarse-grained gray metamorphic rock, likely gneiss or granitic gneiss
Quartz–feldspar–mica gneiss; exact identification requires petrographic or chemical testing
AI-generated identification · may be incorrectGray, granular, and sparkly with visible light quartz/feldspar and dark mica or amphibole; typically Mohs 6–7, vitreous to pearly luster, interlocking crystals, and weak-to-strong foliation. No reliable cleavage is visible at specimen scale.
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Physical properties
Gray, granular, and sparkly with visible light quartz/feldspar and dark mica or amphibole; typically Mohs 6–7, vitreous to pearly luster, interlocking crystals, and weak-to-strong foliation. No reliable cleavage is visible at specimen scale.
Formation & geological history
Formed when granitic or sedimentary protoliths underwent high-temperature, high-pressure metamorphism, commonly during Precambrian to Paleozoic mountain building. The apparent banding/foliation reflects mineral segregation during deformation.
Uses & applications
Used as crushed stone, building stone, paving, and occasionally decorative slabs; attractive pieces are collected but generally have limited gem value.
Geological facts
Gneiss commonly contains the same minerals as granite but shows metamorphic fabric or compositional banding. A polished surface would better reveal foliation and distinguish it from massive granite.
Field identification & locations
Look for alternating light quartz–feldspar and dark mica/amphibole bands, foliation, and a hard scratch-resistant surface; common in ancient continental shields and mountain belts. This photograph could also represent granite, so thin-section or hand-lens examination is recommended.
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