Here's why:

* Foliation: The layered appearance in metamorphic rocks is called foliation. It develops when intense pressure and heat cause minerals to align themselves in a parallel fashion. This is often seen in rocks like slate, schist, and gneiss.

* Non-foliated: Some metamorphic rocks form under conditions where pressure is less directional or where the minerals don't have a preferred alignment. These rocks are referred to as non-foliated. Examples include marble (formed from limestone) and quartzite (formed from sandstone).

In summary: While some metamorphic rocks have distinct layers due to foliation, others do not.