What does the term "argillaceous" imply about a rock?

The term "argillaceous" specifically refers to the dominance of clay minerals in a rock's composition. Rocks described as argillaceous typically have a significant amount of clay, which can affect their physical properties and behavior. This term derives from "argilla," the Latin word for clay, indicating that these rocks display characteristics associated with fine-grained materials, such as increased plasticity, reduced permeability, and often a capacity to hold moisture. The presence of clay can have implications for geological processes, sedimentary environments, and the types of fossils found within such rocks, making them significant in the study of geology.