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