metamorphic
Quartz–feldspar-bearing metamorphic rock, likely gneiss or migmatite
Banded quartzofeldspathic gneiss; chiefly quartz (SiO₂), feldspar, mica, and dark amphibole/biotite
AI-generated identification · may be incorrectHardness about 6–7; mottled gray, cream, brown, and dark green-black, with a dull to glassy luster and coarse interlocking crystals. The irregular light–dark banding and foliated texture suggest gneiss, though the image alone cannot distinguish it confidently from migmatite or altered granite.
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Physical properties
Hardness about 6–7; mottled gray, cream, brown, and dark green-black, with a dull to glassy luster and coarse interlocking crystals. The irregular light–dark banding and foliated texture suggest gneiss, though the image alone cannot distinguish it confidently from migmatite or altered granite.
Formation & geological history
Formed when quartz- and feldspar-rich crustal rocks were subjected to intense heat and pressure during mountain building, commonly at roughly 600–800°C. Such rocks are typically Precambrian to Paleozoic, although younger examples occur.
Uses & applications
Used as crushed aggregate, building stone, paving, and decorative slabs; attractive pieces may be collected but are not normally cut as gemstones.
Geological facts
The pale, glassy areas are probably quartz or feldspar, while dark layers likely contain biotite or amphibole; rusty colors commonly reflect iron oxidation.
Field identification & locations
Look for alternating light and dark mineral bands, coarse grains, strong interlocking texture, and hardness sufficient to scratch glass. Common worldwide in ancient continental shields and metamorphic mountain belts.
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