Does shale form from gneiss

Answer 1

It can, indirectly. Shale is a sedimentary rock. Like many rocks, gneiss can be weathered down to very fine particles to the point that it becomes clay or silt. Those particles can then settle on the bottom of a body of water as mud. Under the pressure of burial, that mud can become shale.

However, gneiss can also form from shale. Under long exposure to enormous heat and pressure shale will becomes slate, further heating and pressure will turn slate into phyllite, phyllite into schist, and schist into gneiss.