Model of structure disorder of illite: preliminary results

This paper presents preliminary results of the structure model of a pure illite sample from Hungary. The clay sample mined in the Tokaj region (Northern Hungary) is composed of predominating illite and minor smectite and quartz. Enrichment by sedimentation in water solvent of the illite fraction led to a nearly pure sample which was fully characterized using conventional microscopic and chemical analyses. Although, illite is a well known clay mineral used for many industrial applications (its crystallinity index is used to establish the degree of illitization in oil source rocks linked to oil generation) a structure model has never been refined to date. This is due to the fact that pure samples to be used for structure characterization are a rarity in nature and because the structure is affected by extensive planar disorder. Thus, the structural characterization of this sample is of great importance for the understanding of the structure of illite in general. The planar disorder prevents a simple structure refinement using the Rietveld method and different algorithms must be used. Here, we present the results of structure simulations of powder patterns using NEWMOD, WILDFIRE and DIFFaX, which reveal the structure features and structure model of disorder. They are a good starting point for the combined structure/microstructure refinement which will be attempted using DIFFaX(+).