The mineralogy and phase equilibrium of Keuper Marl

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Abstract
Summary: Previously, it has been suggested that the existence of a variable clay mineralogy was responsible for the anomalous engineering behaviour of Keuper Marl. Using x-ray diffraction techniques and chemical analyses, it is shown here that 80 per cent of the samples examined fall in the mineral suite illite-corrensite-carbonates-quartz-hematite, and that there is good evidence that this mineral assemblage has attained phase equilibrium. Calculation of the true clay mineral content of the samples analysed shows that much of the clay content is aggregated into silt size units, which accounts for the large range of measured Activities.