igneous
Biotite-bearing granite or granitic gneiss
Quartz–feldspar–biotite granitoid; if foliated, orthogneiss
AI-generated identification · may be incorrectCoarse-grained, gray to tan rock with visible quartz, feldspar, and dark biotite; granular texture and weak foliation or weathering fractures. Hardness is approximately 6–7 Mohs, vitreous to dull luster, poor cleavage overall, and specific gravity about 2.6–2.8.
Identified More igneous →
Explore Biotite-bearing granite or granitic gneiss in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Coarse-grained, gray to tan rock with visible quartz, feldspar, and dark biotite; granular texture and weak foliation or weathering fractures. Hardness is approximately 6–7 Mohs, vitreous to dull luster, poor cleavage overall, and specific gravity about 2.6–2.8.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep in the crust, commonly during Precambrian to Paleozoic continental events; any banding or flattening may reflect later metamorphism. Exact age cannot be determined from the photograph.
Uses & applications
Used as building stone, aggregate, curbing, monuments, and crushed-rock fill; attractive varieties may be polished for countertops and architectural surfaces.
Geological facts
Quartz appears glassy gray, feldspar is pale, and biotite forms black flakes. Distinguishing granite from orthogneiss requires observing whether minerals form consistent compositional banding or a strong planar fabric.
Field identification & locations
Common in continental shields, mountain belts, and granitic plutons worldwide. Field identification relies on coarse interlocking grains, abundant quartz and feldspar, and lack of sedimentary layering; a thin section or geochemical test is needed for certainty.
