metamorphic
Likely gneiss pebble
Foliated quartz–feldspar gneiss, with dark biotite or amphibole
AI-generated identification · may be incorrectCoarse, mottled light and dark mineral grains with weak banding; likely quartz (Mohs 7), feldspar (6), and biotite/amphibole (about 5–6). The image does not show enough detail to confirm composition or cleavage; luster is mostly dull to slightly vitreous.
Identified More metamorphic →
Explore Likely gneiss pebble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Coarse, mottled light and dark mineral grains with weak banding; likely quartz (Mohs 7), feldspar (6), and biotite/amphibole (about 5–6). The image does not show enough detail to confirm composition or cleavage; luster is mostly dull to slightly vitreous.
Formation & geological history
Gneiss forms when existing rocks undergo high-grade heat and pressure, segregating minerals into light and dark bands. Its age depends on its source; the rounded shape suggests transport and abrasion in sediment or stream gravels.
Uses & applications
Gneiss is used as dimension stone, paving and crushed aggregate; this small pebble is mainly a field or collection specimen.
Geological facts
The speckled appearance and possible mineral banding are consistent with gneiss, but other coarse metamorphic rocks can look similar.
Field identification & locations
Look for interlocking grains and compositional bands; a close-up or fresh break would help distinguish gneiss from granite or schist. Gneiss occurs widely in ancient continental crust and glacial or river deposits.
More like this
