metamorphic
Gneiss
Foliated metamorphic rock, likely granitic gneiss; commonly composed of quartz, feldspar, and mica or amphibole
AI-generated identification · may be incorrectCoarse-grained, with mottled pink, gray, and black minerals arranged in weakly visible bands. Quartz and feldspar are about Mohs 6; mica has perfect basal cleavage, while the rock has no single crystal structure or specific gravity.
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Physical properties
Coarse-grained, with mottled pink, gray, and black minerals arranged in weakly visible bands. Quartz and feldspar are about Mohs 6; mica has perfect basal cleavage, while the rock has no single crystal structure or specific gravity.
Formation & geological history
Formed when granitic or sedimentary rock underwent intense heat and pressure, reorganizing minerals into bands. Gneiss forms in deep continental crust, commonly during ancient mountain-building events; the specimen’s age cannot be determined from the image.
Uses & applications
Used as dimension stone, paving, aggregate, and decorative landscaping stone; attractive pieces are collected or used in jewelry and crafts.
Geological facts
Gneiss is identified by mineral segregation into light and dark bands, though banding may be irregular or faint.
Field identification & locations
Look for coarse interlocking grains and streaks or bands of contrasting minerals; common in old continental shields and mountain belts worldwide. This rounded specimen may have been naturally weathered or shaped.
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