metamorphic

Biotite gneiss (probable)

Foliated quartz–feldspar–mica gneiss; commonly containing biotite mica, quartz, and plagioclase/alkali feldspar

AI-generated identification · may be incorrect

Gray, coarse-grained, strongly foliated rock with alternating light and dark mineral bands; minerals show vitreous to pearly luster, and hardness is roughly 6–7 overall (mica flakes are softer).

Identified September 5, 2026More metamorphic →

Explore Biotite gneiss (probable) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Gray, coarse-grained, strongly foliated rock with alternating light and dark mineral bands; minerals show vitreous to pearly luster, and hardness is roughly 6–7 overall (mica flakes are softer).

Formation & geological history

Formed when pre-existing granite or sedimentary rock underwent intense regional metamorphism, producing mineral segregation and foliation; its age depends on locality, commonly Precambrian to Paleozoic.

Uses & applications

Used as crushed stone, building or landscaping stone, and occasionally as decorative slabs; generally has little gemstone value.

Geological facts

The planar texture reflects alignment and recrystallization under directed pressure and high temperature, typically at several kilometers’ depth.

Field identification & locations

Identify it by its alternating quartz–feldspar and dark mica bands, grainy texture, and tendency to split along foliation; common in ancient mountain belts and glacial deposits. A precise identification would require a fresh surface and locality information.