metamorphic
Gneiss
Quartz–feldspar–mica gneiss
AI-generated identification · may be incorrectCoarse-grained, gray and cream with dark minerals and weakly visible banding; typically quartz, feldspar, and biotite or hornblende. Hardness is about 6–7 Mohs; vitreous quartz and feldspar grains contrast with darker, less lustrous minerals.
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Physical properties
Coarse-grained, gray and cream with dark minerals and weakly visible banding; typically quartz, feldspar, and biotite or hornblende. Hardness is about 6–7 Mohs; vitreous quartz and feldspar grains contrast with darker, less lustrous minerals.
Formation & geological history
Formed when pre-existing igneous or sedimentary rock underwent high-grade heat and pressure, segregating minerals into bands. Gneisses span many geological ages; the specimen’s age cannot be determined from the image.
Uses & applications
Used as dimension stone, landscaping material, aggregate, and occasionally decorative slabs or carvings.
Geological facts
Gneiss is identified by coarse mineral grains and compositional banding, though bands can be irregular or subtle.
Field identification & locations
Common in continental shields and mountain belts worldwide. Look for interlocking light quartz–feldspar and dark mica or amphibole; a photograph alone cannot confirm the identification.
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