Final answer:
If a high-grade metamorphic rock like gneiss is exposed to more heat and pressure, it will transform into an ultra-high-grade metamorphic rock known as eclogite.
Step-by-step explanation:
Gneiss, as a very high-grade metamorphic rock, has already undergone intense heat and pressure. However, if it is exposed to even more heat and pressure, it will undergo further metamorphism and transform into an ultra-high-grade metamorphic rock called eclogite.
Migmatite is a complex rock that is formed when a very high-grade metamorphic rock like gneiss is subjected to more heat and pressure. This rock comprises of to some degree dissolved minerals and recrystallized parts, with particular banding and veining designs.