I have no idea what "amorphous" material you think about. The basic igneous rock has the potential in a first step to generate chlorite-vermiculite and smectite as it undergoes chemical weathering due to the cations (Mg, Fe) and the existing pH of the meteoric fluids. In case of an advanced level of weathering and a further drop in the pH, kaolinite-group minerals will come into existence. The last step beyond what we call argillitization is the formation of duricrusts which will end up in Al-, Fe- and Mn oxide hydrates contained in bauxite and ferricretes . Here I suspect to find some amorphous pre-stages. This given pathway is to describe in rather general terms what chemical weathering may leave behind when affecting a basic igneous rock.