Final answer:
Minerals in metamorphic rocks that align parallel to each other are known as foliation. Foliated metamorphic rocks are identified by their mineral alignment, which is the result of heat and pressure, while non-foliated rocks appear massive and lack such alignment.
Step-by-step explanation:
When minerals in metamorphic rocks align parallel to each other, it is referred to as foliation. This planar arrangement of textural features is indicative of metamorphic processes involving heat and pressure that re-crystallize and align minerals perpendicularly to the direction of the pressure. There are different types of foliated rocks, characterized by the size of their mineral grains and the degree of their banding. For example, slate is known for having a very fine-grained, foliated, nonlayered texture, while gneiss is known for its coarse-grained, foliated, layered texture. On the other hand, non-foliated metamorphic rocks do not show this alignment and are often massive and structureless. Metamorphic rocks, such as the foliated phyllite, schist, and non-foliated quartzite and marble, are classified by their textures and mineral compositions, which reflect the temperature and pressure conditions of their metamorphic environment.