metamorphic

Banded gneiss

Gneiss, commonly quartz–feldspar–biotite gneiss

AI-generated identification · may be incorrect

Coarse-grained, strongly foliated rock with alternating tan felsic bands and dark biotite/amphibole-rich layers; quartz and feldspar give a vitreous to dull luster. Hardness is approximately 6–7 Mohs; cleavage is weak overall, with mineral-specific cleavage, and specific gravity is about 2.6–2.8.

Identified September 9, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed by high-grade regional metamorphism of granite, sedimentary rock, or volcanic protoliths, typically under intense heat and pressure during mountain building. Individual specimens may be Precambrian or younger; age cannot be determined from the photograph.

Uses & applications

Used as dimension stone, facing stone, paving, landscaping aggregate, and decorative rock; attractive polished pieces are collected but are generally modestly valuable.

Geological facts

Its characteristic banding records mineral segregation and deformation during metamorphism. The photograph is also consistent with migmatitic or biotite-rich gneiss, but mineral identification would require a close examination or testing.

Field identification & locations

Common in ancient continental shields and metamorphic mountain belts, including the Adirondacks, New England, Scandinavia, India, and parts of Canada. Identify it by coarse grains and compositional banding, distinguishing it from finer-grained schist by its generally massive, blocky texture.