A metamorphic rock in which the grains line up in parallel bands is called a foliated metamorphic rock.

Here's why:

* Foliation: This refers to the parallel alignment of mineral grains within a metamorphic rock. It's created by intense pressure and heat during the metamorphic process.

* Bands: The aligned grains create distinct layers or bands that are visible in the rock.

Examples of foliated metamorphic rocks:

* Slate: Fine-grained, with a smooth, flat surface.

* Schist: Coarse-grained, with visible, shimmering mineral crystals.

* Gneiss: Banded, with alternating layers of light and dark minerals.

Let me know if you have any other questions!