metamorphic

Gneiss pebble

Biotite–quartz–feldspar gneiss, possibly granitic gneiss

AI-generated identification · may be incorrect

Coarse-grained, dark gray to pink-brown, with visible quartz and feldspar-rich patches and dark biotite/amphibole. Likely Mohs 6–7, vitreous to dull luster, granular crystalline texture, poor cleavage as a whole, and specific gravity about 2.6–2.8.

Identified September 22, 2026More metamorphic →

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Physical properties

Formation & geological history

Likely metamorphosed granite or other felsic protolith during Precambrian–Grenville regional metamorphism, then rounded by glacial or stream transport. The reported location near 45.4°N, 73.3°W is consistent with glacially transported Canadian Shield-derived rocks.

Uses & applications

Used as crushed aggregate, dimension stone, landscaping rock, and occasionally as a polished decorative stone; this rounded specimen has modest collector value.

Geological facts

The irregular light-and-dark mineral segregation is typical of gneissic banding, though this pebble may also be a strongly deformed granitic rock. Pink areas are probably potassium feldspar; translucent gray grains are quartz.

Field identification & locations

Look for alternating light and dark mineral-rich zones, interlocking grains, and no obvious vesicles or sedimentary layering. Common around southern Quebec as glacial erratics; confirm with a fresh surface, quartz hardness, and feldspar cleavage.