Adjective
Of the nature of clay; consisting of, or containing, argil or clay; clayey.
Source: Webster's dictionaryargillaceous rocks Source: Internet
Geologically, the island consists of gneiss and argillaceous schists with occasional tufts and other sedimentary layers from which fossils have been recovered. Source: Internet
"Natural" cements correspond to certain cements of the pre-Portland era, produced by burning argillaceous limestones at moderate temperatures. Source: Internet