metamorphic

Gneiss

Quartz–feldspar–mica gneiss

AI-generated identification · may be incorrect

Coarse-grained, pale gray and pink with dark biotite-rich streaks and weak banding; likely Mohs 6–7, vitreous to dull luster, interlocking crystals, and no prominent cleavage as a whole rock. Exact mineral composition cannot be confirmed from the photo.

Identified September 26, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms when granitic or sedimentary rocks undergo high-grade heat and pressure, producing recrystallized minerals and compositional layering. Gneisses occur in ancient continental basement, often billions of years old.

Uses & applications

Used as building and landscaping stone, aggregate, and decorative dimension stone; this rough boulder appears suited mainly to landscaping or collecting.

Geological facts

Gneiss is identified by coarse mineral grains and light–dark segregation; unlike schist, its minerals are commonly arranged in broad bands rather than a uniformly flaky fabric.

Field identification & locations

The specimen’s pale quartz–feldspar matrix and dark streaks are consistent with gneiss, though a photograph cannot establish the identification or locality. Common in old mountain belts and continental shields worldwide.