Banded gneiss

Typically medium- to coarse-grained with pink feldspar, gray quartz, and dark biotite or amphibole in strongly streaked bands; hardness about 6–7, vitreous to dull luster, no consistent cleavage, and specific gravity roughly 2.6–2.8. The specimen appears foliated and compositionally banded, though exact identification from an image is limited.

Formed when granite or other crustal rock underwent intense high-grade metamorphism, commonly during Precambrian orogenies; partial melting may produce irregular light-colored veins. Common in ancient continental shields and deeply eroded mountain belts.

Used as dimension stone, paving, aggregate, monuments, and decorative slabs; attractive polished pieces are collected, but this specimen appears primarily of educational or ornamental value.

Gneissic banding records segregation and alignment of minerals under directed pressure and high temperature, often exceeding about 600°C. Pink bands usually reflect potassium feldspar, while dark bands commonly contain biotite or amphibole.

Identify it by alternating light and dark mineral bands, coarse visible grains, and foliation; unlike layered sedimentary rock, the bands are commonly contorted and crystalline. Common localities include Scandinavia, Canada, the northeastern United States, India, Brazil, and Australia.