Banded gneiss

Typically medium-coarse grained, with alternating light quartz/feldspar and dark biotite or amphibole bands; vitreous to pearly luster, hardness about 6–7, poor cleavage overall, and specific gravity roughly 2.6–2.8. The specimen’s strongly contorted foliation may also indicate migmatitic gneiss or a high-grade metamorphic rock.

Formed when granite or other sedimentary/igneous protoliths undergo intense heat and pressure, causing recrystallization and mineral segregation; commonly Precambrian to Paleozoic, though ages vary widely.

Used as dimension stone, facing stone, countertops, landscaping material, and aggregate; attractive polished pieces are collected but are generally less valuable than rare mineral specimens.

The folded light-dark banding records ductile deformation deep in the crust. Partial melting can produce irregular pale veins and a migmatitic appearance.

Identify it by hard, interlocking grains and compositional banding rather than flat sedimentary layers; quartz scratches glass, while mica forms reflective flakes. Common in ancient continental shields and mountain belts.