Argillite

[ɑ:dʒilait]

(noun.) a sedimentary rock differing from shale in being bound by silica and from slate in having no slate cleavages.

Edited by Lelia--From WordNet

(n.) Argillaceous schist or slate; clay slate. Its colors is bluish or blackish gray, sometimes greenish gray, brownish red, etc.

Edited by Candice