What is the parent rock of the metamorphic rock biotite gneiss?

Answer 1

Biotite gneiss could have a number of protoliths (parent rocks), and those protoliths could be igneous or sedimentary; the sedimentary parent rock could be a fine-grained shale, high in biotite composition, or a granitic rock, high in biotite.

Answer 2

Biotite gneiss typically forms from the high-grade metamorphism of sedimentary rocks such as shale or mudstone. These parent rocks undergo intense heat and pressure, causing their minerals to recrystallize and form the characteristic banding of gneiss, with biotite and other minerals aligning to create a foliated texture.