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

The term "argillaceous" describes a rock that is rich in clay minerals. In geological terms, clay refers to very fine-grained sediment particles that are less than 0.002 millimeters in diameter. Rocks that are classified as argillaceous typically exhibit characteristics associated with clay content, such as being fine-grained, having a smooth texture, and being able to retain moisture.

Clay-rich rocks, such as shales, are formed from the compaction of clay sediments, often in quiet water environments like lakes or deep ocean floors. The presence of clay also influences the rock's physical properties, making it more susceptible to weathering and erosion. Therefore, identifying a rock as argillaceous underscores its significant clay mineral content, which has implications for its behavior in geological processes and its use in various applications.