Argilliferous is an adjective used to describe a type of material or substance that contains or is related to clay. Some synonyms for argilliferous include clayey, clay-bound, loamy and mudstone. Clayey is the most commonly used synonym for argilliferous. It refers to a soil that has a high percentage of clay and is known for its plasticity, or ability to be molded when wet. Clay-bound refers to a soil or rock that is held together by clay. Loamy refers to a soil that has an equal mixture of sand, silt, and clay, creating a fertile and nutrient-rich soil. Mudstone refers to a sedimentary rock that has a highly compacted texture, formed from layers of mud and clay.