metamorphic

Banded gneiss pebble

Gneiss, likely quartz–feldspar–mica gneiss

AI-generated identification · may be incorrect

Hardness about 6–7 Mohs; gray to dark gray with a prominent pale quartz/feldspar band, granular texture, and vitreous to dull luster. Gneiss has no consistent cleavage and typically shows mineral banding from deformation and recrystallization.

Identified August 9, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when pre-existing igneous or sedimentary rock underwent high-grade metamorphism involving intense heat, pressure, and deformation, commonly during mountain building. Its exact geological age cannot be determined from the photograph; gneiss ranges from Archean to recent metamorphic belts.

Uses & applications

Used as crushed aggregate, dimension stone, landscaping stone, and decorative material; small polished pebbles are collected or used in crafts. This specimen is mainly of modest interest as a field or lapidary sample.

Geological facts

The light stripe is probably quartz- or feldspar-rich material, while the darker matrix likely contains biotite, amphibole, or other mafic minerals. Strong compositional banding is the key distinction from more uniform granite.

Field identification & locations

Identify it by alternating light and dark mineral bands, coarse interlocking grains, and lack of sedimentary layering or vesicles; common in Precambrian shields and eroded mountain belts worldwide. A fresh surface and hand lens would improve identification.