metamorphic
Biotite-rich gneiss with a dark mafic band
Banded gneiss, likely quartz–feldspar–biotite gneiss (exact minerals uncertain from the image)
AI-generated identification · may be incorrectCoarse, foliated rock with light quartz/feldspar and a prominent dark, elongate biotite- or amphibole-rich band. Quartz is Mohs 7 and feldspar about 6; overall luster is mostly dull to slightly sparkly, with mineral grains arranged in bands.
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Physical properties
Coarse, foliated rock with light quartz/feldspar and a prominent dark, elongate biotite- or amphibole-rich band. Quartz is Mohs 7 and feldspar about 6; overall luster is mostly dull to slightly sparkly, with mineral grains arranged in bands.
Formation & geological history
Formed when pre-existing rock was recrystallized and segregated into light and dark layers under high heat and pressure. Gneisses span many geological ages and occur in ancient continental basement and metamorphic belts.
Uses & applications
Commonly used as dimension stone, facing stone, landscaping material, and aggregate; attractive banding can make it suitable for decorative slabs.
Geological facts
The alternating mineral bands are called gneissic banding and reflect metamorphic mineral segregation rather than sedimentary layering.
Field identification & locations
Look for coarse interlocking grains and distinct light–dark bands; the image appears to show an outcrop or cut surface, but does not permit definitive mineral identification. Gneiss is widespread in regions such as the Canadian Shield, Scandinavia, and the Scottish Highlands.
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