Argillaceous iron ore

from The Collaborative International Dictionary of English v.0.48

Argillaceous \Ar`gil*la"ceous\, a. [L. argillaceus, fr.
   argilla.]
   Of the nature of clay; consisting of, or containing, argil or
   clay; clayey.
   [1913 Webster]

   {Argillaceous sandstone} (Geol.), a sandstone containing much
      clay.

   {Argillaceous iron ore}, the clay ironstone.

   {Argillaceous schist} or {state}. See {Argillite}.
      [1913 Webster]