Using the approach described in Equation 1, the kaolinite content was confirmed to be ~ 55 wt.%. The kaolinite 001 reflection at 12.3 °2θ (corresponding to a basal spacing of 7.2 Å) in the Fe-rich clay was broader compared to that in the low-Fe clay (Figure ), suggestive of a smaller particle size and/or more disordered crystal structure , as was previously observed for kaolinitic clays of lateritic origin of some halloysite-(7Å) cannot be ruled out, as its diffraction pattern is similar to that of a disordered kaolinite and has reported to be present in the lithomarge layer of the Interbasaltic Formation at some depths . Halloysite-(7Å) refers to the dehydrated form of halloysite (Al2Si2O5) in line with AIPEA recommended nomenclature . However, given the structural and chemical similarities between disordered kaolinite and halloysite-(7Å), they are very difficult to distinguish . The basal spacing (7.2 Å) of the 001 reflection in the low-Fe and Fe-rich clays indicates that the majority of the clay mineral content in the Fe-rich clay is likely to be kaolinite, as halloysite-(7Å) typically has a slightly higher basal spacing in the range of . Another factor likely contributing to the broader reflections and higher signal-to-noise ratio of the Ferich clays' diffraction patterns (compared to the low-Fe clays' patterns) was Fe-K fluorescence arising from the substantial quantity of Fe (hydr)oxides and/or oxides present in the Fe-rich clays . After calcination, the kaolinite 001 reflection in the Fe-rich clay XRD pattern was no longer detectable. A small, broad reflection at 20.4 °2θ was observed in the pattern of the calcined Fe-rich clay. Amongst the associated minerals, goethite and magnetite underwent a thermal decomposition to form hematite. The TG curve for the asreceived Fe-rich clay (Figure ) showed the dehydroxylation of kaolinite in the temperature range of 300-600°C, and the thermal decomposition of goethite in the temperature range of 200-350°C . The TG curve of the Fe-rich clay has a similar profile to the TG curves of other lateritic clays containing kaolinite and goethite, with the lower dehydroxylation temperature of the Fe-rich clay (relative to the low-Fe clay) attributed to the greater extent of structural disorder of kaolinite in the Fe-rich clay . For the calcined Fe-rich clay, negligible mass loss was observed over 300-600°C, indicating that dehydroxylation was complete after calcination at 750°C (consistent with the low Fe clays). The TEM images of the un-calcined Fe-rich clay (Figure ) showed a noticeably smaller size of individual particles (but not agglomerates) compared to the low-Fe clay (Figure ). These fine-scale observations are in agreement with bulk measurements of specific surface area: