argillaceous minerals

Argillaceous minerals may appear silvery upon optical reflection and are minerals containing substantial amounts of clay-like components ( = clay). Argillaceous components are fine-grained (less than 2 µm)  aluminosilicates, and more particularly clay minerals such as kaolinite, montmorillonite-smectite, illite, and chlorite.  Claystone and shales are thus predominantly argillaceous.