Here's why:

* Foliation: This refers to the parallel arrangement of mineral grains within the rock. It's a result of intense pressure during the metamorphic process, causing minerals to align themselves in layers. This creates a layered or banded appearance in the rock. Examples of foliated metamorphic rocks include slate, schist, and gneiss.

While foliation is the most common characteristic, other important characteristics include:

* Recrystallization: The original minerals in the rock are changed into new minerals due to heat and pressure.

* Texture: Metamorphic rocks often have unique textures, such as banded, schistose, or gneissic.

* Mineral Composition: The specific minerals present in a metamorphic rock depend on the original rock type and the metamorphic conditions.

Let me know if you have any other questions about metamorphic rocks!