metamorphic

Quartz-rich gneiss

Foliated quartz–feldspar–mica gneiss, possibly migmatitic

AI-generated identification · may be incorrect

Hardness about 6–7; gray to dark gray with white quartz/feldspar and rusty iron-oxide veining. Vitreous quartz luster, coarse crystalline texture, and weak-to-strong foliation; no obvious cleavage in quartz-rich areas.

Identified September 7, 2026More metamorphic →

Explore Quartz-rich gneiss in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed when older igneous or sedimentary rock underwent high-grade metamorphism, causing mineral recrystallization and banding; commonly Precambrian to Paleozoic, depending on locality.

Uses & applications

Used locally as building stone, riprap, aggregate, and landscaping rock; attractive polished pieces may be used decoratively, but this irregular specimen has modest commercial value.

Geological facts

The pale, glassy zones are likely quartz, while dark bands may contain biotite, amphibole, or other ferromagnesian minerals. Rust-colored streaks commonly represent weathered pyrite or iron-bearing minerals.

Field identification & locations

Identify by alternating light and dark mineral bands, coarse interlocking grains, and resistance to scratching; quartz should resist a steel knife. Common in ancient continental shields and metamorphic mountain belts; exact identification requires a fresh surface or laboratory testing.