metamorphic
Weathered granitic gneiss
Granitic gneiss; quartz–feldspar–mica rock
AI-generated identification · may be incorrectTypically medium-grained, gray and weakly banded with quartz and feldspar mosaics plus dark biotite/hornblende. Hardness about 6–7 Mohs, vitreous to dull luster, massive to foliated texture, poor cleavage, and specific gravity roughly 2.6–2.8.
Identified More metamorphic →
Explore Weathered granitic gneiss in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically medium-grained, gray and weakly banded with quartz and feldspar mosaics plus dark biotite/hornblende. Hardness about 6–7 Mohs, vitreous to dull luster, massive to foliated texture, poor cleavage, and specific gravity roughly 2.6–2.8.
Formation & geological history
Formed when granite or another felsic igneous rock was subjected to intense regional metamorphism, recrystallization, and deformation, commonly during Precambrian to Paleozoic mountain building. The surface is strongly weathered, obscuring the banding.
Uses & applications
Used as dimension stone, building or landscape rock, aggregate, and occasionally polished architectural stone; generally not a gemstone material.
Geological facts
Gneiss commonly preserves alternating light quartz–feldspar and dark mica-rich bands, recording high-temperature metamorphism. This specimen may also be a massive, weathered granitic rock where foliation is subtle.
Field identification & locations
Identify by its hard, speckled quartz–feldspar appearance and faint compositional banding; quartz scratches glass, while feldspar commonly shows blocky cleavage. Common in Precambrian shields and metamorphic mountain belts worldwide.
More like this
