metamorphic
Banded gneiss pebble
Gneiss, likely quartz–feldspar gneiss with a dark biotite- or amphibole-rich band
AI-generated identification · may be incorrectRounded, mottled tan, gray, and black bands; likely quartz and feldspar with dark mica or amphibole. Quartz is Mohs 7 and feldspar about 6; the rock has a granular texture and no obvious cleavage at this scale. Exact mineral proportions cannot be confirmed from the photo.
Identified More metamorphic →
Explore Banded gneiss pebble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Rounded, mottled tan, gray, and black bands; likely quartz and feldspar with dark mica or amphibole. Quartz is Mohs 7 and feldspar about 6; the rock has a granular texture and no obvious cleavage at this scale. Exact mineral proportions cannot be confirmed from the photo.
Formation & geological history
Gneiss forms when pre-existing rocks undergo high-grade heat and pressure, segregating minerals into bands. Its age depends on its source; gneiss ranges from Archean to much younger geological periods.
Uses & applications
Commonly collected as a pebble or used decoratively as aggregate and landscaping stone; this small specimen has little practical industrial value.
Geological facts
The alternating light and dark bands are called gneissic banding and reflect mineral segregation during metamorphism.
Field identification & locations
Look for coarse, interlocking grains and distinct irregular light-dark bands; similar gneiss occurs in ancient continental shields and mountain belts worldwide. A definite identification requires closer examination than the image allows.
More like this
