Question #9b85c
1 Answer
They are formed under high heat and/or pressure.
Explanation:
This is a generic answer. Another is that they are often layered or banded (foliated), or non-foliated. It's generally considered that these rocks - which are formed by transitioning pre-existing rocks, known as protoliths - into new rocks, that often greatly differ from their parent rocks. An example is how shale regionally metamorphoses to form a series of other rocks, including slate, schist, and gneiss.
The transition generally occurs beneath the lithosphere, where pressures are much greater than the surface of the earth (where other rocks are capable of forming, like extrusive igneous and sedimentary rocks), which correlates partially to very high temperatures. Eventually, through uplift and erosion, the metamorphic rocks end up on the surface of the planet, where we see them today.
