metamorphic
Garnet-bearing gneiss
Quartz–feldspar–mica gneiss with iron-rich garnet (commonly almandine)
AI-generated identification · may be incorrectCoarse, strongly foliated metamorphic rock with gray quartz/feldspar bands, reddish-brown garnet or iron-oxide-rich patches, and dark mica/amphibole. Hardness is approximately 6–7 overall; garnet is about 6.5–7.5 Mohs, with vitreous to pearly luster and no prominent cleavage.
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Physical properties
Coarse, strongly foliated metamorphic rock with gray quartz/feldspar bands, reddish-brown garnet or iron-oxide-rich patches, and dark mica/amphibole. Hardness is approximately 6–7 overall; garnet is about 6.5–7.5 Mohs, with vitreous to pearly luster and no prominent cleavage.
Formation & geological history
Formed when preexisting igneous or sedimentary rock underwent high-grade regional metamorphism involving intense heat, pressure, and deformation; commonly Precambrian to Paleozoic in age. The banding reflects mineral segregation during metamorphism.
Uses & applications
Used locally as decorative stone, aggregate, and building or landscaping material; attractive pieces are collected, though this specimen appears mainly of educational interest.
Geological facts
Gneiss commonly preserves a visible mineral banding or compositional layering, unlike most granite. Reddish grains may be garnet, but confirmation requires a close examination or hardness and density tests.
Field identification & locations
Common in continental shields and deeply eroded mountain belts, including Scandinavia, the Alps, India, Canada, and the eastern United States. Look for alternating light and dark bands, coarse interlocking grains, and garnet crystals; value is typically $5–$25 for a hand specimen, or $25–$100 if garnet-rich and attractive.
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