Gneiss is a protolith of migmatite.

Rock group	Metamorphic
Metamorphism type	Regional
Metamorphic rock class	Metapelitic Metabasic (mafic gneiss) Marl Granitic (granitic gneiss)
Protoliths	Schist Igneous rocks such as granite

Gneiss in Hand Sample

Paleoproterozoic gneiss from Clear Creek Canyon, CO
Archean-aged basement complex gneiss from the Wyoming Craton
Biotite–muscovite–garnet Maidens gneiss (note that that’s four separate links)
Augen gneiss
Big honkin’ augen in Paleoproterozoic augen gneiss from Clear Creek Canyon, CO
Augen gneiss from Shetland
Folded Lewisian gneiss on a beach in Scotland

Gneiss in Thin Section

Maidens gneiss, plane polars
Maidens gneiss, crossed polars
Sillimanite–garnet gneiss, plane polars
Sillimanite–garnet gneiss, crossed polars
Augen gneiss, plane polars
Augen gneiss, crossed polars
Biotite gneiss, plane polars
Biotite gneiss, crossed polars

Sillimanite-garnet gneiss, plane polars

Sillimanite-garnet gneiss in plane polarized light. Magnification: 40x Click here for crossed polars: https://youtu.be/R1e5-r02YQY Click here to explore this…

Sillimanite-garnet gneiss, crossed polars

Sillimanite-garnet gneiss in cross polarized light. Magnification: 40x Click here for plane polars: https://youtu.be/Y-uJ8SQWPZA Click here to explore this s…

Biotite gneiss, plane polars

Biotite gneiss in plane polarized light. Magnification: 40x Click here for crossed polars: Click here to explore this slide in plane polars: https://viewer.g…

Biotite gneiss, crossed polars

Biotite gneiss in cross polarized light. Magnification: 40x Click here for plane polars: https://youtu.be/4EG3QZ7nnII Click here to explore this slide in pla…