Modelling X-ray diffraction by lamellar structures composed of electrically charged layers

The stacking parameters and nature of a mixed-layer mineral (m.l.m.) are generally determined by modelling its X-ray diffraction pattern. For m.l.m.'s containing electrically charged layers it has been assumed, until now, that they can be described by stacking of electrically neutral units that associate the charged layer itself and a compensating interlayer charge. Some consequences of this hypothesis are difficult to justify, e.g. quite different charges to compensate the same types of interlayers, or, on the contrary, the same charge to compensate quite different types of interlayers. A new model is proposed, allowing a description of any lamellar structure containing electrically charged layers. The mathematical formalism for the diffracted intensities of such a model is developed.