ARGILLITE
argillite
(noun) a sedimentary rock differing from shale in being bound by silica and from slate in having no slate cleavages
Source: WordNet® 3.1
Noun
argillite (plural argillites)
(geology) A fine-grained sedimentary rock, intermediate between shale and slate, sometimes used as a building material
Source: Wiktionary
Ar"gil*lite, n. Etym: [Gr. -lite.] (Min.)
Definition: Argillaceous schist or slate; clay slate. Its colors is bluish
or blackish gray, sometimes greenish gray, brownish red, etc.
– Ar`gil*lit"ic, a.
Source: Webster’s Unabridged Dictionary 1913 Edition