Migmatitic gneiss

Typically medium- to coarse-grained, with pale quartz/feldspar bands and dark biotite or amphibole; Mohs hardness about 6–7, vitreous to pearly luster, no consistent cleavage as a whole, and strongly foliated/banded texture. The image may show partial-melting textures and weathering, though exact identification is uncertain without a scale or fresh surface.

Forms when preexisting crustal rocks undergo high-grade metamorphism, commonly around 650–800°C, with partial melting producing migmatitic veins. Such rocks are generally Precambrian to Paleozoic and occur in deep continental crust and ancient mountain belts.

Used as dimension stone, facing stone, countertops, paving, monuments, and aggregate; attractive polished pieces are collected but are less commonly used as gemstones.

The irregular light and dark layers record intense deformation and mineral segregation; pale leucosome may represent crystallized melt, while darker melanosome retains biotite-rich residue.

Identify it by alternating light felsic and dark mafic bands, foliation, and interlocking grains; distinguish it from granite by its planar fabric. Common in shield regions and deeply eroded mountain belts.