metamorphic

Banded gneiss pebble

Gneiss, typically quartz–feldspar–mica bearing

AI-generated identification · may be incorrect

Medium- to coarse-grained, with alternating pale quartz/feldspar and darker biotite-rich bands; vitreous to pearly luster, irregular fracture, and constituent-mineral hardnesses of about 2.5–7 Mohs. The rounded form indicates natural river or beach abrasion.

Identified August 31, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms when granite or other continental crust undergoes intense regional metamorphism, commonly during Precambrian to Paleozoic mountain-building; mineral segregation creates the distinctive banding.

Uses & applications

Used as dimension stone, architectural facing, landscaping aggregate, and decorative or educational specimens; this small pebble has mainly collecting value.

Geological facts

Gneissic banding records deep-crustal heat and pressure and may be folded or streaked. It can resemble banded marble, but visible granular quartz/feldspar and mica favor gneiss.

Field identification & locations

Look for coarse interlocking grains and compositional bands rather than flat sedimentary layers; a glassy quartz grain, feldspar cleavage, and dark flaky mica are diagnostic. Common in ancient continental shields and glacial or river deposits.