What does argillaceous mean?
The definition of argillaceous
Etym: [L. argillaceus, fr. argilla.]
Of the nature of clay; consisting of, or containing, argil or clay; clayey. Argillaceous sandstone (Geol.), a sandstone containing much clay.
— Argillaceous iron ore, the clay ironstone.
— Argillaceous schist or state. See Argillite.