metamorphic

Banded gneiss

Quartzo-feldspathic gneiss, likely biotite-bearing

AI-generated identification · may be incorrect

Hardness about 6–7; coarse-grained, with white quartz and feldspar bands contrasting with dark biotite or amphibole-rich layers. It has a granular texture, vitreous to pearly luster, and lacks prominent cleavage as a whole rock.

Identified September 5, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when preexisting granite or other felsic rock underwent intense regional metamorphism, producing compositional banding and recrystallization, typically during Precambrian to Paleozoic mountain-building. Exact age cannot be determined from the photograph.

Uses & applications

Used as dimension stone, paving, landscaping aggregate, and occasionally decorative slabs; attractive pieces are collected but are generally modestly valued.

Geological facts

The alternating light and dark layers are called gneissic banding and record mineral segregation under high temperature and pressure. The rock appears to contain minor dark inclusions or mafic bands.

Field identification & locations

Identify it by its coarse crystals and planar light–dark banding, unlike layered sedimentary rock; quartz scratches glass, while feldspar is commonly white and blocky. Common in ancient continental shields and exposed mountain cores.