metamorphic

Gneiss with a polished reddish-brown stone

Banded granitoid gneiss; the foreground pebble may be jasper or iron-rich quartzite

AI-generated identification · may be incorrect

The host rock is coarse-grained, gray, speckled, and weakly banded, with quartz, feldspar, and dark mica/amphibole; hardness about 6–7 Mohs and generally nonmetallic luster. The smooth reddish-brown pebble is likely a separate polished iron-oxide-rich silica stone, but its identity cannot be certain from the image.

Identified August 19, 2026More metamorphic →

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Physical properties

Formation & geological history

Gneiss forms when granite or other crustal rocks undergo high-grade metamorphism, commonly during Precambrian mountain-building; many examples are over 1 billion years old. The pebble likely formed by silica-rich sedimentary or volcanic processes and later weathering and transport.

Uses & applications

Gneiss is used as dimension stone, architectural facing, paving, and aggregate; attractive pieces are collected. Jasper or quartzite is used for cabochons, beads, landscaping, and ornamental objects.

Geological facts

Distinct mineral segregation or banding distinguishes gneiss from massive granite, although this specimen appears relatively weakly banded. Iron oxides commonly produce red, brown, and maroon colors in jasper and quartzite.

Field identification & locations

Look for alternating light quartz-feldspar and dark mica/amphibole-rich bands, granular texture, and no obvious sedimentary layering; fresh surfaces are more diagnostic. Common in ancient continental shields and metamorphic mountain belts worldwide.