What characteristic defines foliated rocks?

Foliated rocks are specifically characterized by their distinct layering or banding that occurs due to the alignment of mineral grains under directed pressure during metamorphism. This alignment creates a series of parallel bands or layers, giving foliated rocks their unique appearance. The pressure causes minerals, such as micas or chlorites, to become flattened and oriented in a specific direction, leading to the foliation feature.

In contrast, other options do not accurately describe foliated rocks. The formation process of foliated rocks involves both temperature and pressure, rather than high temperature alone. Additionally, foliated rocks certainly contain minerals; in fact, the arrangement of mineral grains is a defining characteristic. Lastly, foliated rocks are not exclusively igneous; they are primarily metamorphic, as their formation involves transforming pre-existing rocks under heat and pressure.