metamorphic

Banded metamorphic rock, likely gneiss

Biotite–quartz–feldspar gneiss (probable); exact identification requires testing

AI-generated identification · may be incorrect

Dark gray to black, coarse-grained and strongly foliated, with a pale quartz–feldspar band. Typical hardness is about 6–7 Mohs, vitreous to dull luster, granular crystal texture, and little or no cleavage as a whole rock.

Identified September 5, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when preexisting igneous or sedimentary rock underwent high-grade heat and pressure, segregating minerals into bands during regional metamorphism. It may represent Precambrian to younger continental crust; age cannot be determined from the photograph.

Uses & applications

Used as dimension stone, paving, aggregate, and decorative landscaping material; attractive polished pieces may be collected, but this specimen appears common rather than gem-grade.

Geological facts

The alternating light and dark bands are mineral segregation, not simple surface staining. Dark layers commonly contain biotite, amphibole, or other mafic minerals, while light layers are quartz and feldspar.

Field identification & locations

Identify it by its persistent mineral banding, interlocking grains, and resistance to scratching; a steel file should generally not scratch quartz-rich areas. Common worldwide in exposed mountain belts and ancient continental shields.