metamorphic

Quartz-rich gneiss (probable banded metamorphic rock)

Gneiss; composition chiefly quartz, feldspar, and mica, possibly with amphibole

AI-generated identification · may be incorrect

Coarse-grained, strongly foliated and banded, with gray-white quartz/feldspar layers and darker biotite- or amphibole-rich bands. Hardness is approximately 6–7 Mohs; vitreous to pearly luster, no single cleavage, and specific gravity about 2.6–2.8.

Identified September 6, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when preexisting granite or sedimentary rock underwent high-grade regional metamorphism, commonly during Precambrian to Paleozoic mountain building. The pictured specimen may also show later fracturing and weathering.

Uses & applications

Used as dimension stone, building aggregate, landscaping rock, and occasionally as polished architectural stone; attractive pieces are collected but are usually modestly valuable.

Geological facts

Gneiss commonly preserves alternating mineral bands produced by recrystallization and partial mineral segregation under intense heat and pressure. It can resemble granite, but its minerals are arranged in distinct planar or wavy bands.

Field identification & locations

Identify it by visible foliation, alternating light and dark bands, coarse interlocking grains, and a lack of vesicles. Common in ancient continental shields and metamorphic mountain belts; typical hand specimens sell for about $5–$30, with polished or unusually patterned pieces reaching $50–$150.