metamorphic
Weathered granitic gneiss
Quartz–feldspar–biotite gneiss (likely granitic gneiss)
AI-generated identification · may be incorrectCoarse-grained, strongly foliated and banded, with gray quartz and feldspar and dark biotite or amphibole; rusty-orange staining is likely iron oxides. Typical minerals have Mohs hardness 6–7 (quartz) and 6 (feldspar); exact mineral proportions and specific gravity cannot be determined from the image.
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Physical properties
Coarse-grained, strongly foliated and banded, with gray quartz and feldspar and dark biotite or amphibole; rusty-orange staining is likely iron oxides. Typical minerals have Mohs hardness 6–7 (quartz) and 6 (feldspar); exact mineral proportions and specific gravity cannot be determined from the image.
Formation & geological history
Formed when granitic rock was deeply buried and recrystallized under high heat and pressure, producing mineral segregation and foliation. Its age cannot be established from appearance alone; gneisses range from ancient Precambrian to younger rocks.
Uses & applications
Gneiss is used as dimension stone, paving, crushed aggregate, and decorative stone; this exposed outcrop is not a jewelry material.
Geological facts
The alternating light and dark bands record mineral rearrangement during metamorphism, while orange-brown areas commonly reflect weathering of iron-bearing minerals.
Field identification & locations
Identify it by coarse interlocking crystals and compositional banding or foliation; distinguish it from unfoliated granite by the aligned, streaked texture. Gneiss is widespread in old continental shields and mountain belts.
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