the Fe-rich clay had a much higher specific surface area (59.8 m 2 g -1 ) than the low-Fe clay (6.7 m 2 g -1 ), despite the Fe-rich clay having a slightly lower kaolinite content (see Table in Supplementary Information). These pieces of evidence support the interpretation of the greater width of the 001 kaolinite reflection in the XRD pattern of the Fe-rich clay, relative to the low-Fe clay, being due to the Fe-rich clay's fine kaolinite particle size (Figure ). The plate-like morphology of the stacked particles is indicative of disordered kaolinite; however, the presence of some particles of halloysite-(7Å) with a plate-like or elongated tubular morphology cannot be excluded. Similar to the low-Fe clays, calcination had a modest disruptive effect on stacking of kaolinite particles in the calcined Fe-rich clay (Figure ) compared to the raw Fe-rich clay (Figure ). can exist in a variety of sizes depending on formation and weathering processes, including as very fine particles which can be adhered to the surfaces of clay mineral particles . Substitution of Fe for octahedral Al in kaolinite can occur depending on its weathering route , but the extent of substitution is limited to a minor percentage, estimated as < 4% . Within this range, lateritic kaolinites have a relatively high proportion of Fe substitution in comparison to kaolinites formed via other routes . Therefore, whilst octahedral Fe in kaolinite may have accounted for the weak Fe signal observed in the areas corresponding to kaolinite platelets (Figure ), the particles which exhibited a strong Fe signal were confidently identified as Fe-based minerals. In the calcined Fe-rich clay, Fe-based minerals (predominantly hematite, as identified via XRD in Figure ) were still present as very fine particles after the thermal decomposition of goethite to hematite (Figure ). EEL spectra of the Fe-rich clays were normalised to the main Al K-edge peak of kaolinite as described previously in Section 3.1 (Figure ). The kaolinite in the Fe-rich clay contained a greater proportion of 4/5-fold Al than the kaolinite in the low-Fe clay, on the basis of the higher intensity at the edge onset (1572 eV) of the Fe-rich clay's spectrum (Figure vs Figure ). A higher proportion of 4/5-fold Al is consistent with the lateritic origins of the Fe-rich clay being more conducive to structural disorder in kaolinite , in comparison to the more ordered kaolinite expected from the mixed residual and hydrothermal origins of the low-Fe clay . In the calcined clay's spectrum, there was an increase in relative intensity at the onset of the Al K-edge profile, associated with an increase in 4-and 5-fold Al (relative to the as-received clay's spectrum). A greater change in Al K-edge profile upon calcination was observed for the low-Fe clay than the calcined Fe-rich clay. A lower 4/5-fold Al content of the calcined Fe-rich clay compared to the calcined low-Fe clay is plausible, given the known variation in Al distribution between different metakaolins . Halloysite-(7Å), which could be present to some extent in the Fe-rich clay, exhibits very similar Al coordination to kaolinite both before and after calcination , and so would not be expected to significantly change the EEL spectra if present.