The physical properties of three montmorillonites before and after heating were studied by reflectance colorimetry, X-ray diffraction (XRD) and infrared (IR) and Mössbauer spectroscopies. Colorimetric data, though not directly relatable to sample mineralogy, provide cheap and rapid information on the temperatures of sample breakdown. X-ray diffraction provides information on sample mineralogy and the transformations that develop during firing and allows the major phases formed in the course of firing to be identified, whereas IR data provide information on water and hydroxyl loss and the final breakdown of the montmorillonite structure. Mössbauer spectroscopy gives information on Fe2+ oxidation (where applicable) and reveals subtle variations in Fe site coordination and Fe mineralogy, including the formation of Fe oxides – that can be quantified in proportions as low as 0.1% – following structural breakdown of the montmorillonites.

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