metamorphic

Coarse-grained metamorphic rock, likely gneiss

Granitic gneiss; typically quartz + feldspar + biotite/hornblende

AI-generated identification · may be incorrect

Hardness about 6–7 Mohs; gray, black, and white mottled appearance with granular texture and weakly visible foliation. Nonmetallic luster, interlocking crystals, and no obvious cleavage as a whole rock; identification is limited by the image.

Identified September 10, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when granite or another felsic rock underwent high-grade metamorphism, recrystallizing under intense heat and pressure. Commonly Precambrian to Paleozoic in age, though gneiss forms in many mountain belts.

Uses & applications

Used locally as dimension stone, landscaping rock, riprap, and aggregate; attractive pieces may be polished for decorative slabs. This irregular specimen has little commercial value.

Geological facts

Gneiss commonly shows alternating light quartz-feldspar bands and darker mica or amphibole bands, though some varieties are strongly mottled rather than distinctly banded.

Field identification & locations

Look for interlocking quartz and feldspar grains, dark mica/amphibole, and mineral alignment or banding; a streak test is generally unhelpful. Common in ancient continental shields and exposed mountain cores worldwide.