Gneiss

Typically medium- to coarse-grained with pale and dark mineral banding, vitreous quartz, and feldspar with pearly mica; hardness about 6–7 Mohs, nonfoliated-to-strongly foliated, with poor cleavage overall.

Formed by high-grade metamorphism of granite or other silica-rich rocks, commonly during Precambrian mountain-building and crustal reworking. The visible specimen shows compositional streaking and possible weathering along foliation.

Used as building and facing stone, paving, landscaping rock, and aggregate; attractive polished varieties are used decoratively. Common specimens generally have modest collector value.

Gneissic banding develops when minerals recrystallize and segregate under intense heat and pressure without fully melting. It can resemble granite, but its mineral alignment and banding indicate metamorphism.

Identify it by alternating light quartz–feldspar bands and darker mica/amphibole layers, plus a tendency to split along foliation; the image is consistent with weathered gneiss, though exact identification requires a fresh surface or hand sample tests. Common worldwide in ancient continental shields and mountain belts.