Amorphous matter in kaolins and its geological implications

Selective dissolution with ammonium oxalate was carried out to extract amorphous matter in some kaolins from China. Ammonium oxalate extraction is an effective method to extract amorphous constituents without destroying the kaolinite crystalline structure. The study showed that, absolute amounts of amorphous constituents in kaolins are in the order Al>Si>Fe, but that relative amounts are in the order Fe>Al>Si. The amorphous phases are probably mainly in the form of separate particles, or colloidal particles absorbed on the surface of kaolinite particles. Compared to older kaolins, younger kaolins contain much more amorphous iron content.