Which type of rock formation involves the arrangement of crystals in bands?

The arrangement of crystals in bands is characteristic of foliated rocks. This texture occurs due to the alignment of mineral grains under directed pressure, often during the metamorphic process. The pressure causes the dominant minerals in the rock to realign along parallel planes, resulting in a layered or banded appearance.

Foliated metamorphic rocks, such as schist or gneiss, exhibit this banding and layering, which is a fundamental aspect of their formation and distinguishes them from other rock types. In contrast, unfoliated rocks do not exhibit this banding due to a lack of directional pressure, while sedimentary rocks are typically formed from particles and do not exhibit the same crystalline textures. Therefore, the correct answer is clearly linked to the distinctive banding feature present in foliated metamorphic rocks.