igneous
Dark granite or granitic gneiss slab
Quartz–feldspar–biotite granite; possibly foliated granitic gneiss
AI-generated identification · may be incorrectFine- to medium-grained, dark gray-brown surface with pale quartz/feldspar speckling and irregular darker mineral patches; typically Mohs 6–7, vitreous to dull luster, interlocking crystals, and no cleavage as a whole rock.
Identified More igneous →
Explore Dark granite or granitic gneiss slab in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Fine- to medium-grained, dark gray-brown surface with pale quartz/feldspar speckling and irregular darker mineral patches; typically Mohs 6–7, vitreous to dull luster, interlocking crystals, and no cleavage as a whole rock.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep underground; gneiss forms when granite is strongly metamorphosed. Such rocks are commonly Precambrian to Phanerozoic, but the image alone cannot establish age.
Uses & applications
Used widely as dimension stone, countertops, flooring, monuments, aggregate, and landscaping material; attractive polished pieces may be sold as architectural or decorative stone.
Geological facts
The mottled appearance likely reflects quartz, feldspar, and dark biotite or hornblende. Surface scratches and wear indicate this may be a polished or heavily used stone slab rather than a fresh hand specimen.
Field identification & locations
Look for visible interlocking quartz and feldspar grains, dark mica/hornblende, and—if gneissic—alternating mineral bands. Common worldwide in continental shields and mountain belts; a thin section or fresh broken surface would be needed for confident identification.
