metamorphic
Weathered garnet-bearing gneiss
Quartz–feldspar–mica gneiss with almandine garnet, chiefly Fe₃Al₂(SiO₄)₃
AI-generated identification · may be incorrectCoarse, foliated metamorphic rock with pale quartz/feldspar, dark mica, and reddish-brown garnet-like grains; garnet hardness 6.5–7.5 Mohs, vitreous luster, no cleavage, while the rock is hard and granular. The specimen’s rounded surface indicates weathering and transport.
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Physical properties
Coarse, foliated metamorphic rock with pale quartz/feldspar, dark mica, and reddish-brown garnet-like grains; garnet hardness 6.5–7.5 Mohs, vitreous luster, no cleavage, while the rock is hard and granular. The specimen’s rounded surface indicates weathering and transport.
Formation & geological history
Formed when shale or granitic protolith underwent high-grade regional metamorphism, typically during mountain building; exact age cannot be determined from the image and may range from Precambrian to younger. Common in continental mountain belts and glacial or stream gravels.
Uses & applications
Used as dimension stone, landscaping aggregate, riprap, and decorative stone; attractive garnet-bearing pieces are collected but generally have low gemstone value unless garnets are clear and well-formed.
Geological facts
Gneiss commonly shows compositional banding from mineral segregation, though this hand specimen appears strongly weathered. Garnet-bearing gneiss is often mistaken for granite because both can be coarse and quartz-rich.
Field identification & locations
Look for alternating light and dark mineral bands, granular quartz/feldspar, mica sheen, and embedded reddish garnets; a streak, hardness, and thin-section test would confirm identification. Found widely in ancient crystalline terrains, including the Adirondacks, New England, Scandinavia, and parts of Canada.
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