metamorphic
Polished banded gneiss, possibly garnet-bearing
Gneiss; composition likely quartz–feldspar–mica, with accessory amphibole or garnet
AI-generated identification · may be incorrectTypically Mohs 6–7, gray to silver with dark, strongly wavy foliation; vitreous to pearly luster and interlocking crystalline texture. The visible rounded piece appears polished or naturally smoothed, while the slab shows planar banding and a fresh dark-gray surface.
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Physical properties
Typically Mohs 6–7, gray to silver with dark, strongly wavy foliation; vitreous to pearly luster and interlocking crystalline texture. The visible rounded piece appears polished or naturally smoothed, while the slab shows planar banding and a fresh dark-gray surface.
Formation & geological history
Formed by high-grade regional metamorphism of granite or sedimentary protoliths, commonly during Precambrian to Paleozoic mountain-building events. Intense heat and pressure segregated minerals into light and dark bands.
Uses & applications
Used as dimension stone, architectural cladding, landscaping stone, countertops, and decorative polished specimens; generally modest jewelry value except when unusually attractive or garnet-rich.
Geological facts
Gneissic banding is compositional layering rather than sedimentary bedding. It commonly contains quartz, feldspar, biotite, hornblende, and sometimes garnet.
Field identification & locations
Identify it by alternating light quartz/feldspar and dark mica/amphibole bands, visible foliation, and hardness sufficient to scratch glass; unlike slate, it is coarse crystalline and not evenly fissile. Common in ancient continental shields and metamorphic mountain belts.
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