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In this study, Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC) and thermogravimetry (TGA) are used as complementary techniques to investigate structural order and phase transformation associated with thermal decomposition of selected kaolins from South Africa and Cameroon. The samples exhibit poorly resolved, weak intensity OH stretching and bending vibrations of structural water, characteristic kaolinite dehydroxylation temperatures (500 -560 o C), low to high mass loss (6.5 to 19.4 %) and asymmetrical DSC curves. The results infer poor to partially ordered structures associated with significant quartz and iron oxide contamination. Compared against other commercial kaolins, the studied samples show moderate to good potentials for use in structural ceramics and refractories. ARTICLE INFO

Nine geophagic material samples were analysed in order to characterise their mineralogical and elemental constituents, and infer on their health threats. Most abundant mineral in the samples was quartz, followed by smectite, kaolinite and muscovite in minor; and microcline, plagioclase, and goethite in trace quantities. Dominant major oxides were SiO

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Field mapping, colour, particle size distribution, pH and x-ray diffraction studies were undertaken to elucidate the genesis of Ediki kaolin. The kaolin occurs within the Mungo formation of upper cretaceous age, ascribed to the Douala sedimentary basin. The kaolin profile consists of upward coarsening sandstonesiltstonesandstone sequence with a gradient of 35 to 40°. Texturally, the kaolin is mainly silt loam with a constitution of sand (18.1 to 24 wt.%), silt (68 to 73.3 wt.%) and clay (7 to 13.5 wt.%). The pH of the sample is acidic with values ranging from 4.8 to 5. Kaolinite and quartz are the dominant mineralogical phases whereas, muscovite + microcline and illite + goethite occur as minor and trace phases respectively. High porosity and permeability of the sandstones favoured migration of fluids which enhanced the formation of secondary diagenetic minerals. The presence of detrital feldspars and mica grains in the sandstones, were favourable parent phases for kaolinite formation. Kaolinization was further enhanced by the hot humid tropical climate, acidic pH, fairly gentle relief (40°), low K and Na concentrations (inferred from the mineralogy), as well as the low energy depositional environment.