The Collaborative International Dictionary
Argillitic
Argillite \Ar"gil*lite\, n. [Gr. ? clay + -lite.] (Min.) Argillaceous schist or slate; clay slate. Its colors is bluish or blackish gray, sometimes greenish gray, brownish red, etc. -- Ar`gil*lit"ic, a.
Wiktionary
argillitic
a. Relating to, or containing, argillite.