Source: The Collaborative International Dictionary of English v.0.48
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.
[1913 Webster]