\Ar`gil*la"ceous\, a. [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}.