What type of metamorphic rock is not layered?

Unfoliated rocks are indeed characterized by their lack of layering. This type of metamorphic rock forms under uniform pressure and temperature conditions, which allows the minerals to grow and interlock without being subjected to the directional forces that create layering. As a result, unfoliated rocks often exhibit a more massive or homogeneous structure.

Foliated rocks, in contrast, develop distinct layers or bands due to the alignment of minerals caused by differential pressure. This structural difference is significant, as it reflects the metamorphic processes that acted upon the rock. The mention of sedimentary and igneous rocks in the context of this question is pertinent, but they do not fall under the category of metamorphic rocks. Sedimentary rocks are formed from the accumulation of sediment, while igneous rocks are formed from cooled magma or lava, neither of which involves the metamorphic processes that lead to foliation or unfoliation.